Arduino Si4735 radio library Si4735 library
Arduino and Silicon Laboratories Si4735 radio library
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\begin_body
\begin_layout Title
Library for Silicon Laboratories Si4735 radio receiver chip and an Arduino
microcontroller
\end_layout
\begin_layout Author
Copyright 2012, 2013, 2015, 2018 Michael J.
Kennedy
\end_layout
\begin_layout Standard
This program is free software: you can redistribute it and\SpecialChar breakableslash
or modify it under
the terms of the GNU Lesser General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE.
See the GNU Lesser General Public License for more details.
To view a copy of the GNU Lesser General Public License, visit these two
web pages:
\end_layout
\begin_layout Quote
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status open
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http://www.gnu.org/licenses/gpl-3.0.html
\end_layout
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status open
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http://www.gnu.org/licenses/lgpl-3.0.html
\end_layout
\end_inset
\end_layout
\begin_layout Standard
This software can be found at the following web site:
\end_layout
\begin_layout Quote
\begin_inset Flex URL
status open
\begin_layout Plain Layout
https://sourceforge.net/projects/arduino-si4735/files/
\end_layout
\end_inset
\end_layout
\begin_layout Standard
The Mercurial repository can be downloaded with the following shell command:
\end_layout
\begin_layout LyX-Code
hg clone http://hg.code.sf.net/p/arduino-si4735/si4735 Si4735
\end_layout
\begin_layout Standard
To report bugs or make suggestions contact me at:
\end_layout
\begin_layout Quote
michael.joseph.kennedy.1970 [_a_t_] gmail [dot] com
\end_layout
\begin_layout Standard
This library is a fork of previous libraries.
Older versions can be found here:
\end_layout
\begin_layout Itemize
Ryan Owens,
\begin_inset Flex URL
status open
\begin_layout Plain Layout
https://www.sparkfun.com/products/10342
\end_layout
\end_inset
\end_layout
\begin_layout Itemize
Wagner Sartori Junior,
\begin_inset Flex URL
status open
\begin_layout Plain Layout
https://github.com/trunet/Si4735
\end_layout
\end_inset
\end_layout
\begin_layout Itemize
Jon Carrier,
\begin_inset Flex URL
status open
\begin_layout Plain Layout
https://github.com/jjcarrier/Si4735
\end_layout
\end_inset
\end_layout
\begin_layout Standard
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\begin_layout Description
\series bold
Warning: This library is
\bar under
not
\bar default
completely compatible with these other versions of the library! Most importantl
y, usage of begin() has been changed.
\series default
\series bold
\emph on
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You MUST change your code! If you don't, the program will still compile,
but fail to work correctly!
\series default
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See
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LatexCommand formatted
reference "sec:Initializing-the-radio"
\end_inset
\begin_inset Quotes eld
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LatexCommand nameref
reference "sec:Initializing-the-radio"
\end_inset
\begin_inset Quotes erd
\end_inset
below for further details.
\end_layout
\end_inset
\end_layout
\begin_layout Standard
This library can be used with the following SparkFun boards:
\end_layout
\begin_layout Itemize
DEV-10342,
\begin_inset Quotes eld
\end_inset
SI4735 AM & FM Receiver Shield,
\begin_inset Quotes erd
\end_inset
\begin_inset Flex URL
status open
\begin_layout Plain Layout
http://www.sparkfun.com/products/10342
\end_layout
\end_inset
\end_layout
\begin_layout Itemize
WRL-10906,
\begin_inset Quotes eld
\end_inset
Si4735 FM/AM Radio Receiver Breakout,
\begin_inset Quotes erd
\end_inset
\begin_inset Flex URL
status open
\begin_layout Plain Layout
http://www.sparkfun.com/products/10906
\end_layout
\end_inset
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\begin_layout Standard
Both contain a Si4735-C40 radio receiver chip.
The library was tested with a shield marked on the bottom with a date of
\begin_inset Quotes eld
\end_inset
4\SpecialChar breakableslash
14\SpecialChar breakableslash
11.
\begin_inset Quotes erd
\end_inset
\end_layout
\begin_layout Standard
The Si4735 supports all modes available in the Si47xx family except for
Weather Band (WB) receive and FM transmit.
As a result, most chips in this family can be used with this library, if
you are careful to not access missing modes.
In some cases, small modifications to the library may be needed for full
compatibility.
Note: We do not yet support the auxiliary input mode found on the Si4735-D60
or later.
Also note: The Si4700\SpecialChar breakableslash
01\SpecialChar breakableslash
02\SpecialChar breakableslash
03\SpecialChar breakableslash
08\SpecialChar breakableslash
09 chips are older and use a completely different
command syntax.
Therefore, they cannot be used with this library.
\end_layout
\begin_layout Standard
This library supports all current Arduinos including the 2009 (Duemilanove),
Uno, Mega, Mega 2560, Leonardo, and Due.
\end_layout
\begin_layout Standard
To understand how to use this library, you
\series bold
MUST
\series default
read this document and the
\family sans
Si4735.h
\family default
file.
You should also read through the example applications found in the
\family sans
examples
\family default
directory.
It will also be helpful to read the comments in the source code.
Everything has been heavily commented to make understanding and customizing
the library easy.
\end_layout
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\begin_layout Description
Warning: If you are going to either view or edit the library's source code
or the
\family sans
Changes.text
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file, you
\series bold
\bar under
MUST
\series default
\bar default
use a
\series bold
\bar under
programmer's text editor
\series default
\bar default
.
I recommend one of the following, multi-platform editors:
\end_layout
\begin_deeper
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Geany:
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http://www.geany.org/
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SciTE:
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status open
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http://www.scintilla.org/SciTE.html
\end_layout
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\begin_layout Description
Note: I have not yet tested the Arduino Due code because I do not currently
have this board.
\end_layout
\begin_layout Description
Note: I have not yet tested the I2C code because the Si4735 shield I used
for testing does not permit using I2C.
Also, I do not currently have the breakout board which can use I2C.
\end_layout
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\begin_layout Section
Background information
\end_layout
\begin_layout Standard
For more information on the Silicon Labs Si4735, see the following documents.
(Check SparkFun and Silicon Labs web sites.):
\end_layout
\begin_layout Itemize
Data sheet: Si4734\SpecialChar breakableslash
35-C40 — Gives hardware description.
(Get version on SparkFun web site.)
\end_layout
\begin_layout Itemize
Application Note: AN332:
\begin_inset Quotes eld
\end_inset
Si47xx Programming Guide
\begin_inset Quotes erd
\end_inset
— Explains the Si4735 (and similar chips) from a software perspective.
\end_layout
\begin_deeper
\begin_layout Standard
Warning: The
\begin_inset Quotes eld
\end_inset
Si47xx Programming Guide
\begin_inset Quotes erd
\end_inset
implies that each command returns a status byte with the current interrupts.
However, in most cases, the status byte contains random garbage.
The exceptions are:
\end_layout
\begin_layout Itemize
The CTS interrupt is always up-to-date.
The radio chip always updates the CTS bit in the status byte whenever the
CTS interrupt changes.
Therefore, you can always get the current status of CTS by reading the
status byte, regardless of the previous command sent.
\end_layout
\begin_layout Itemize
A few commands return a status byte with their interrupt updated:
\end_layout
\begin_deeper
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Command
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Interrupt
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TUNE_STATUS
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STC
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RSQ_STATUS
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RSQ
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RDS_STATUS
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RDS
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When an interrupt pulse is received by the Arduino, the only way to accurately
know the status of the non CTS interrupts is to send the GET_INT_STATUS
command and then read its status byte.
\end_layout
\end_deeper
\begin_layout Itemize
Application Note: AN383:
\begin_inset Quotes eld
\end_inset
Si47xx Antenna, Schematic, Layout, and Design Guidelines
\begin_inset Quotes erd
\end_inset
— Gives important information on designing antennas for the radio.
Please note that the Si4735 shield is based on the design given in section
10
\begin_inset Quotes eld
\end_inset
Whip Antenna for SW Receive on AMI
\begin_inset Quotes erd
\end_inset
(page 46 in revision 0.6.)
\end_layout
\begin_layout Section
Using the SparkFun Si4735 Arduino Shield
\end_layout
\begin_layout Standard
The SparkFun Si4735 Arduino Shield requires modification to work correctly:
\end_layout
\begin_layout Itemize
There is no voltage level shifting on Si4735's GPO1 (MISO) and GPO2 (INT)
outputs.
The Si4735 must run at 3.3 V while most Arduinos run at 5 V.
The shield converts all Arduino outputs to 3.3 V logic levels but does nothing
to the Si4735 outputs.
This is a problem because, when running at 5 V, an input must reach 3 V
for the AVR to treat it as high (V
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IH
\end_layout
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):
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\begin_inset Formula $V_{CC}\times.6=5V\times.6=3V$
\end_inset
\end_layout
\begin_layout Standard
However, the minimum guaranteed output voltage for a high signal from the
Si4735 radio chip is (V
\begin_inset script subscript
\begin_layout Plain Layout
OH
\end_layout
\end_inset
):
\end_layout
\begin_layout Quote
\begin_inset Formula $V_{IO}\times.8=3.3V\times.8=2.64V$
\end_inset
\end_layout
\begin_layout Standard
Because the radio chip's output for a high signal can be less than the 3
V required by the AVR, either some form of level shifting from 3.3 V to
5 V must be added or an Arduino running at 3.3 V must be used.
3.3 V Arduinos include the Due, the 3.3 V versions of the Pro and Pro Mini
from SparkFun, and the Seeeduino set to run at 3.3 V.
\end_layout
\begin_layout Standard
See
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LatexCommand formatted
reference "sec:Level-shifting"
\end_inset
\begin_inset Quotes eld
\end_inset
\begin_inset CommandInset ref
LatexCommand nameref
reference "sec:Level-shifting"
\end_inset
\begin_inset Quotes erd
\end_inset
below for more information.
\end_layout
\end_deeper
\begin_layout Itemize
The AREF pin is connected to ground on the shield's printed circuit board.
AREF should never be grounded as this makes using the AVR's analog to digital
converter impossible.
Fixing this is optional if you do not need analog to digital conversion.
However, you never know what changes you will make to your radio project
in the future.
\end_layout
\begin_deeper
\begin_layout Standard
To fix this, you need to break the connection between the Arduino's AREF
input and ground.
Probably the best solution is to cut the eight tiny traces between the
pad and ground plane with a sharp knife, X-Acto blade, or razor blade.
There are four traces on each side of the circuit board.
Do this before soldering a connector to the shield.
\end_layout
\begin_layout Standard
Another option is to use a connector that does not connect the shield's
AREF pad to the Arduino's AREF input.
\end_layout
\end_deeper
\begin_layout Itemize
The RF\SpecialChar breakableslash
Antenna section is based on application note AN383, section 10
\begin_inset Quotes eld
\end_inset
Whip Antenna for SW Receive on AMI,
\begin_inset Quotes erd
\end_inset
page 46 in revision 0.6.
However, there is one small difference: The application note shows a connection
between the other pin of the double throw switch and the AM loop antenna.
This shorts out the 33 pF capacitor when the switch is in AM mode.
SparkFun omitted this connection.
Fixing this mistake is only needed for AM Medium Wave (common AM service)
and Long Wave reception.
However, if you do fix it, it should improve AM Medium Wave reception.
On my board, RSSI (signal strength) went up by 5.
\end_layout
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\begin_layout Standard
Note: The switch is mislabeled by SparkFun as
\begin_inset Quotes eld
\end_inset
AM\SpecialChar breakableslash
LW
\begin_inset Quotes erd
\end_inset
and
\begin_inset Quotes eld
\end_inset
FM\SpecialChar breakableslash
SW.
\begin_inset Quotes erd
\end_inset
It should be labeled as
\begin_inset Quotes eld
\end_inset
FM\SpecialChar breakableslash
AM\SpecialChar breakableslash
LW
\begin_inset Quotes erd
\end_inset
and
\begin_inset Quotes eld
\end_inset
SW.
\begin_inset Quotes erd
\end_inset
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Using the SparkFun Si4735 shield with various Arduinos
\end_layout
\begin_layout Standard
The SparkFun Si4735 shield only supports the
\begin_inset Quotes eld
\end_inset
original
\begin_inset Quotes erd
\end_inset
Arduinos usually based on the ATMega328P including the 2009 (Duemilanove),
Uno, and their clones.
The problem is that the Mega, Leonardo, and Due have their SPI port located
on different pins than the shield.
As a result, you cannot plug the shield into these Arduinos.
Instead, you must use wires and connectors to build a custom cable between
these Arduinos and the shield.
\end_layout
\begin_layout Standard
The pin assignments for the SPI port can be found in Table
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reference "tab:SPI-pin-assignments"
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.
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Shield
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Mega
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Leonardo
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Due
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Name
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Pin
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Pin
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Pin
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Pin
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MOSI
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11
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51
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16
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75
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MISO
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12
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50
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14
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74
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SCK
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13
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52
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15
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76
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\begin_layout Plain Layout
Pin assignments for the SPI port
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LatexCommand label
name "tab:SPI-pin-assignments"
\end_inset
\end_layout
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Standard
On the Leonardo and Due, the MISO, SCK, and MOSI pins are only available
on the ICSP connector.
See:
\begin_inset Flex URL
status open
\begin_layout Plain Layout
http://arduino.cc/en/Reference/SPI
\end_layout
\end_inset
.
\end_layout
\begin_layout Section
Adapting the library to use the SparkFun Si4735 breakout board
\end_layout
\begin_layout Standard
This library can be adapted to make use of all of the Si4735 breakout board's
features by passing arguments to
\family sans
begin()
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and
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setMode()
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and occasionally by manually editing the top part of the
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Si4735.h
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file.
\end_layout
\begin_layout Subsection
Selecting SPI or I2C
\end_layout
\begin_layout Standard
Unlike the Si4735 shield, the Si4735 breakout board can use either the SPI
or I2C bus.
By default, the library uses SPI.
You can switch to I2C by commenting out the
\begin_inset Quotes eld
\end_inset
\family typewriter
#define Si47xx_SPI
\family default
\begin_inset Quotes erd
\end_inset
line by adding
\begin_inset Quotes eld
\end_inset
\family typewriter
//
\family default
\begin_inset Quotes erd
\end_inset
to the beginning like this:
\end_layout
\begin_layout LyX-Code
//#define Si47xx_SPI
\end_layout
\begin_layout Standard
Note: For your convenience, there are two versions of this library available
for download.
One for SPI users and one for I2C users.
The only difference is the defining of the
\family sans
Si47xx_SPI
\family default
macro and which bus library the example programs include.
\end_layout
\begin_layout Standard
The Si4735 has very specific power up requirements which the library will
handle for you by controlling the radio's power and reset pins.
By default, power is controlled by Arduino pin 8 and reset by Arduino pin
9.
\end_layout
\begin_layout Standard
When powering up, the radio must be told to use SPI or I2C.
No action is required to select I2C.
To select SPI, the radio's interrupt (GPO2) pin must be driven high.
This should be done with a 10 k
\begin_inset Formula $\Omega$
\end_inset
pull-up resistor connected between the radio's interrupt pin and 3.3 V.
(Note that this is how the Si4735 shield selects SPI.)
\end_layout
\begin_layout Description
Warning: I2C support requires version 1.0.0 or above of the Arduino development
software.
\end_layout
\begin_layout Subsection
\begin_inset CommandInset label
LatexCommand label
name "subsec:Configuring-SPI"
\end_inset
Configuring SPI
\end_layout
\begin_layout Standard
The library defaults to Arduino pin 10 as the Slave Select (SS) for the
radio's SPI port on all Arduinos.
This assignment is arbitrary and can be changed in
\family sans
Si4735.h
\family default
by breakout board users.
\end_layout
\begin_layout Subsection
\begin_inset CommandInset label
LatexCommand label
name "subsec:Configuring-interrupts"
\end_inset
Configuring interrupts
\end_layout
\begin_layout Standard
By default, the library
\emph on
usually
\emph default
uses Arduino pin 2 as the interrupt input for compatibility with the Si4735
shield.
However, you may change this by editing
\family sans
RADIO_INT_PIN
\family default
and
\family sans
RADIO_EXT_INT
\family default
in
\family sans
Si4735.h
\family default
.
\end_layout
\begin_layout Standard
\family sans
RADIO_INT_PIN
\family default
gives the Arduino pin number to use and
\family sans
RADIO_EXT_INT
\family default
gives the corresponding AVR interrupt number.
When using an AVR based Arduino, if you change one of these, you
\series bold
\emph on
must
\series default
\emph default
change the other so that it matches Table
\begin_inset CommandInset ref
LatexCommand ref
reference "tab:IRQ-Pin-to-IRQ-Num"
\end_inset
below!
\end_layout
\begin_layout Description
Note: Pins 2 and 3 are used by the I2C port on the Leonardo.
Because of this, when I2C is selected on the Leonardo, the interrupt input
is moved to pin 7.
\end_layout
\begin_layout Standard
Please note that ARM based Arduinos such as the Due do not use
\family sans
RADIO_EXT_INT
\family default
.
Also, they can use any pin as the interrupt input.
\end_layout
\begin_layout Standard
Each type of AVR based Arduino has its interrupt inputs on different pins.
Table
\begin_inset CommandInset ref
LatexCommand ref
reference "tab:IRQ-Pin-to-IRQ-Num"
\end_inset
gives the Arduino pin number (
\family sans
RADIO_INT_PIN
\family default
) and its corresponding AVR interrupt number (
\family sans
RADIO_EXT_INT
\family default
) for each type of Arduino board.
\begin_inset Float table
placement H
wide false
sideways false
status open
\begin_layout Plain Layout
\noindent
\align center
\begin_inset Tabular
<lyxtabular version="3" rows="15" columns="3">
<features tabularvalignment="middle">
<column alignment="left" valignment="top" width="0pt">
<column alignment="center" valignment="top" width="0pt">
<column alignment="center" valignment="top" width="0pt">
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\series bold
Arduino pin
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\series bold
AVR interrupt
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\series bold
AVR based Arduino
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\series bold
RADIO_INT_PIN
\end_layout
\end_inset
</cell>
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\begin_inset Text
\begin_layout Plain Layout
\series bold
RADIO_EXT_INT
\end_layout
\end_inset
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</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\begin_inset Quotes eld
\end_inset
Original,
\begin_inset Quotes erd
\end_inset
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2
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0
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Uno, etc.
\end_layout
\end_inset
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<cell alignment="center" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
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3
\end_layout
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<cell alignment="center" valignment="top" bottomline="true" usebox="none">
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1
\end_layout
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<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
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Mega,
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" usebox="none">
\begin_inset Text
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21
\end_layout
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<cell alignment="center" valignment="top" usebox="none">
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0
\end_layout
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<row>
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Mega 2560
\end_layout
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20
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1
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19
\end_layout
\end_inset
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2
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18
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3
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\end_layout
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2
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4
\end_layout
\end_inset
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<row>
<cell alignment="left" valignment="top" bottomline="true" usebox="none">
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3
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5
\end_layout
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<row>
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\begin_inset Text
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Leonardo
\end_layout
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3
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0
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2
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1
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0
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2
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\end_layout
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<cell alignment="center" valignment="top" usebox="none">
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1
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3
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\end_layout
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7
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<cell alignment="center" valignment="top" usebox="none">
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6
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\end_inset
\end_layout
\begin_layout Plain Layout
\begin_inset Caption Standard
\begin_layout Plain Layout
Mapping from AVR Interrupt Pin to Interrupt Number
\begin_inset CommandInset label
LatexCommand label
name "tab:IRQ-Pin-to-IRQ-Num"
\end_inset
\end_layout
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Description
Warning: The AVR's hardware interrupt numbers for the Mega and Mega 2560
do
\series bold
not
\series default
match the interrupt numbers used when calling
\family sans
attachInterrupt()
\family default
! Use the hardware interrupt numbers from the above table, not the interrupt
numbers used with
\family sans
attachInterrupt()
\family default
!
\end_layout
\begin_layout Standard
Please note that pin 7 on the Leonardo is a valid interrupt input, despite
the fact that
\family sans
attachInterrupt()
\family default
does not currently support it.
\end_layout
\begin_layout Subsection
Configuring the radio's clock input
\end_layout
\begin_layout Standard
If
\family sans
MODE_OPT_NO_XTAL
\family default
is passed to
\family sans
setMode()
\family default
, the library will set XOSCEN to false in ARG1 of the POWER_UP command.
Otherwise, XOSCEN will be true in ARG1 of the POWER_UP command.
\end_layout
\begin_layout Standard
\family sans
MODE_OPT_NO_XTAL
\family default
should
\emph on
not
\emph default
be passed to
\family sans
setMode()
\family default
when a 32768 Hz crystal is attached to the radio's RCLK and GPO3 pins.
(This is how the Si4735 shield and the Si4707 breakout board are setup.
Therefore, users of these boards should call
\family sans
setMode()
\family default
without
\family sans
MODE_OPT_NO_XTAL
\family default
.) Other methods of supplying the radio with a clock signal should call
\family sans
setMode()
\family default
with
\family sans
MODE_OPT_NO_XTAL
\family default
.
(For example,
\family sans
setMode(FM, MODE_OPT_NO_XTAL)
\family default
.) See the POWER_UP command in the
\begin_inset Quotes eld
\end_inset
Si47xx Programming Guide
\begin_inset Quotes erd
\end_inset
for more information on the XOSCEN argument.
\end_layout
\begin_layout Standard
If you want digital audio output on the Si4735, you must generate a suitable
clock signal for the radio and send it to the radio's RCLK or DCLK (GPO3)
pin.
You must also enable digital audio output by specifying the correct audio
mode when calling
\family sans
setMode()
\family default
.
See section 5.15
\begin_inset Quotes eld
\end_inset
Reference Clock
\begin_inset Quotes erd
\end_inset
in the Si4735 data sheet and the REFCLK_FREQ and REFCLK_PRESCALE properties
in the
\begin_inset Quotes eld
\end_inset
Si47xx Programming Guide.
\begin_inset Quotes erd
\end_inset
\end_layout
\begin_layout Section
\begin_inset CommandInset label
LatexCommand label
name "sec:Level-shifting"
\end_inset
Level shifting between 5 and 3.3 volts
\end_layout
\begin_layout Standard
The Si4735 must run at 3.3 V or less.
Most Arduinos run at 5 V.
When using these Arduinos, level shifting is required.
Level shifters work in either one direction (unidirectional) or in both
directions (bidirectional).
I2C requires a bidirectional shifter with open drain (open collector) outputs
while SPI and the other I\SpecialChar breakableslash
O signals only require a unidirectional shifter.
\end_layout
\begin_layout Description
Warning: If the Arduino and radio chip will be sharing the SPI bus with
other chips, then the radio's MISO pin (labeled GPO1 in the data sheet)
requires a level shifter with a 3-state output.
\end_layout
\begin_layout Description
Caution: All unused inputs on any chip should be connected to something
to keep the chip stable and reduce power consumption.
The three easiest ways to do this are to connect an unused input to either
ground, the chip's power pin (labeled V
\begin_inset script subscript
\begin_layout Plain Layout
DD
\end_layout
\end_inset
or V
\begin_inset script subscript
\begin_layout Plain Layout
CC
\end_layout
\end_inset
), or a pull-up resistor also connected to the chip's power pin.
\end_layout
\begin_layout Subsection
Unidirectional level shifting from 5 to 3.3 volts
\end_layout
\begin_layout Standard
This converts a high voltage (5 V) output from the Arduino to a low voltage
(3.3 V) for the radio's input by using chips with high voltage tolerant
inputs.
\end_layout
\begin_layout Itemize
A simple and reliable high to low shifter is the 74HC4050 buffer gate.
This is the shifter found on the SparkFun Si4735 shield.
It can shift at least a 15 V signal to as little as 3 V.
\end_layout
\begin_deeper
\begin_layout Standard
To use this chip with the radio, connect the 74HC4050's power pin (labeled
V
\begin_inset script subscript
\begin_layout Plain Layout
DD
\end_layout
\end_inset
or V
\begin_inset script subscript
\begin_layout Plain Layout
CC
\end_layout
\end_inset
) to 3.3 V and the GND pin to ground.
Then connect an Arduino output to a buffer gate's input.
Finally, connect the gate's output to the radio's input.
\end_layout
\end_deeper
\begin_layout Itemize
A newer chip that can do high to low level shifting is the SN74LVC244 3-state
buffer gate, which can shift from a maximum of 5.5 V down to as little as
1.65 V.
As of this writing, this chip is available from Texas Instruments in DIP
form.
\end_layout
\begin_deeper
\begin_layout Standard
To use this chip with the radio, connect the 74LVC244's power pin (labeled
V
\begin_inset script subscript
\begin_layout Plain Layout
DD
\end_layout
\end_inset
or V
\begin_inset script subscript
\begin_layout Plain Layout
CC
\end_layout
\end_inset
) to 3.3 V and the GND pin to ground.
Then connect an Arduino output to a buffer gate's input.
Finally, connect the gate's output to the radio's input.
To make the 74LVC244 work, you must also enable its outputs by grounding
its two Output Enable (1OE and 2OE) pins.
\end_layout
\end_deeper
\begin_layout Subsection
Unidirectional level shifting from 3.3 to 5 volts
\end_layout
\begin_layout Standard
This converts a low voltage (3.3 V) output from the radio to a high voltage
(5 V) for the Arduino's input.
\end_layout
\begin_layout Standard
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
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width "100col%"
special "none"
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\begin_layout Description
DANGER: Other people's versions of this library (including the version from
SparkFun) always seem to drive the INT (GPO2) and MISO (GPO1) pins high
to select SPI mode.
However, the data sheet clearly says you do not need to drive MISO high
to select SPI.
Also, driving INT high is unnecessary with the Si4735 shield because it
includes a pull-up resistor on the radio's INT pin.
This version of the library does not drive the INT or MISO pins high.
If you use a unidirectional level shifter, then you
\series bold
\bar under
MUST
\series default
\bar default
either use this version of the library or modify the other version's source
code to prevent driving these pins high.
Otherwise, you will be temporarily connecting two outputs, which
\series bold
\bar under
WILL
\series default
\bar default
eventually damage your hardware!
\end_layout
\end_inset
\end_layout
\begin_layout Itemize
Many years ago, it was common to mix CMOS and TTL families of chips.
(Today, we only use CMOS.) Because these two families are incompatible,
special versions of CMOS chips were made with TTL compatible inputs.
The two most important families with this feature are named HCT and AHCT.
Notice the
\begin_inset Quotes eld
\end_inset
T
\begin_inset Quotes erd
\end_inset
at the end of the names! The chips in these families accept an input of
2 V through 5 V as a valid high signal.
As a result, these chips are ideal for level shifting from 3.3 V to 5 V.
\end_layout
\begin_deeper
\begin_layout Standard
Caution: Because the HCT and AHCT chips must have 5 V applied to their power
pin (labeled V
\begin_inset script subscript
\begin_layout Plain Layout
DD
\end_layout
\end_inset
or V
\begin_inset script subscript
\begin_layout Plain Layout
CC
\end_layout
\end_inset
), these chips can only be used when level shifting to 5 V.
\end_layout
\begin_layout Standard
As mention above, the radio's MISO pin should have a level shifter with
a 3-state output.
A chip with that ability is the 74AHCT125 3-state buffer gate chip.
It contains four buffer gates, each with an independent active low Output
Enable (OE) pin to control the 3-state capability.
(Note: You may substitute a 74HCT125 chip if you want.)
\end_layout
\begin_layout Standard
To use the 74AHCT125, connect the chip's power pin (labeled V
\begin_inset script subscript
\begin_layout Plain Layout
DD
\end_layout
\end_inset
or V
\begin_inset script subscript
\begin_layout Plain Layout
CC
\end_layout
\end_inset
) to 5 V and GND pin to ground.
Then connect as follows:
\end_layout
\begin_layout Standard
To level shift the radio's MISO (GPO1) pin, connect it to the input of a
buffer gate on the 74AHCT125.
Then connect the gate's output to the Arduino's MISO input.
Finally, connect the buffer gate's Output Enable pin directly to the Arduino's
Slave Select (SS) pin.
(Arduino pin 10 by default.
See
\begin_inset CommandInset ref
LatexCommand formatted
reference "subsec:Configuring-SPI"
\end_inset
\begin_inset Quotes eld
\end_inset
\begin_inset CommandInset ref
LatexCommand nameref
reference "subsec:Configuring-SPI"
\end_inset
\begin_inset Quotes erd
\end_inset
to change this.)
\end_layout
\begin_layout Standard
To level shift the radio's interrupt (GPO2) pin, connect it to the input
of a buffer gate on the 74AHCT125.
Then connect the gate's output to the Arduino's interrupt input.
(Usually Arduino pin 2.
See
\begin_inset CommandInset ref
LatexCommand formatted
reference "subsec:Configuring-interrupts"
\end_inset
\begin_inset Quotes eld
\end_inset
\begin_inset CommandInset ref
LatexCommand nameref
reference "subsec:Configuring-interrupts"
\end_inset
\begin_inset Quotes erd
\end_inset
for more information.) Finally, connect the buffer gate's Output Enable
pin to ground to keep the output
\begin_inset Quotes eld
\end_inset
on
\begin_inset Quotes erd
\end_inset
at all times.
\end_layout
\begin_layout Standard
Because chips in the AHCT family are a recent design, they are robust and
can operate at very high speeds.
(About 100 MHz for the 74AHCT125.) As a result, I recommend using a 74AHCT125
chip when unidirectional level shifting from 3.3 to 5 volts.
\end_layout
\end_deeper
\begin_layout Itemize
A robust low to high voltage level shifter is a gate with an open drain
output such as the 74HC266 exclusive-nor gate.
To use this chip for level shifting, do the following: The gate chip's
power pin (labeled V
\begin_inset script subscript
\begin_layout Plain Layout
DD
\end_layout
\end_inset
or V
\begin_inset script subscript
\begin_layout Plain Layout
CC
\end_layout
\end_inset
) is connected to 3.3 V and the GND pin is connected to ground.
One of the gate's inputs is connected to 3.3 V and the other input is connected
to an Si4735 output that requires level shifting.
Then the gate's output is connected to the Arduino's input.
Finally, each gate output used requires a separate 4.7 k
\begin_inset Formula $\Omega$
\end_inset
pull-up resistor connected to 5 V.
\end_layout
\begin_deeper
\begin_layout Standard
The schematic in Figure
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Open-drain-level-shift"
\end_inset
summarizes how to convert each signal.
\end_layout
\begin_layout Standard
\begin_inset Float figure
placement H
wide false
sideways false
status open
\begin_layout Plain Layout
\noindent
\align center
\begin_inset Graphics
filename Open drain.svg
lyxscale 200
scale 175
\end_inset
\begin_inset Caption Standard
\begin_layout Plain Layout
Open drain level shifter
\begin_inset CommandInset label
LatexCommand label
name "fig:Open-drain-level-shift"
\end_inset
\end_layout
\end_inset
\end_layout
\end_inset
Because pull-up resistors are slow to bring the signal high, this level
shifter only operates at slower speeds.
I conservatively estimate it can handle 1 MHz or less.
\end_layout
\end_deeper
\begin_layout Itemize
The MC14504B or CD4504B chip is a robust, low to high level shifter.
No pull-up resistor is required.
Because this chip is a very old design, this level shifter only operates
at slower speeds.
I conservatively estimate it can handle 1 MHz or less.
\end_layout
\begin_layout Itemize
The CD40109B chip is a robust, low to high level shifter that is very similar
to the MC14504B, however, the CD40109B is slower.
\end_layout
\begin_layout Subsection
Bidirectional level shifting between 3.3 and 5 volts
\end_layout
\begin_layout Standard
This converts between a low voltage input or output on the radio and a high
voltage input or output on the Arduino.
The level shifting circuit automatically detects if the two sides change
direction.
All of these options can be used with either SPI, I2C, or any other I\SpecialChar breakableslash
O
signal, unless otherwise specified.
\end_layout
\begin_layout Standard
Please note that some of these options have 3-state outputs controlled by
an active
\emph on
high
\emph default
Output Enable pin.
However, SPI's MISO signal requires a 3-state output controlled by an active
\emph on
low
\emph default
Output Enable pin connected to Slave Select (SS).
Because none of these options support this, they cannot easily be used
to level shift SPI's MISO signal, if the Arduino and radio are sharing
the SPI bus with other devices.
\end_layout
\begin_layout Itemize
The TXB0108 chip is designed as a robust general purpose level shifter.
Adafruit sells a
\begin_inset CommandInset href
LatexCommand href
name "breakout board"
target "http://www.adafruit.com/products/395"
\end_inset
\begin_inset Foot
status open
\begin_layout Plain Layout
http://www.adafruit.com/products/395
\end_layout
\end_inset
with this chip.
Because this chip is a recent design, it can operate at very high speeds
(20 MHz).
Note that this chip will not work if either side has a pull-up resistor
less than 50 k
\begin_inset Formula $\Omega$
\end_inset
.
Because I2C requires a stronger pull-up resistor, typically 10 k
\begin_inset Formula $\Omega$
\end_inset
, and because I2C requires a level shifter with open drain outputs (which
this chip does not do), this level shifter cannot be used with I2C.
\end_layout
\begin_layout Itemize
The TXS0102 chip is designed as a robust I2C level shifter.
Unfortunately, no one is currently selling a breakout board with this chip.
\end_layout
\begin_layout Itemize
It is possible to build a bidirectional level shifter with a transistor
and two pull-up resistors.
A version of this circuit is available from SparkFun as part
\begin_inset CommandInset href
LatexCommand href
name "BOB-8745"
target "http://www.sparkfun.com/products/8745"
\end_inset
\begin_inset Foot
status open
\begin_layout Plain Layout
http://www.sparkfun.com/products/8745
\end_layout
\end_inset
and from
\begin_inset CommandInset href
LatexCommand href
name "Adafruit"
target "http://www.adafruit.com/products/757"
\end_inset
\begin_inset Foot
status open
\begin_layout Plain Layout
http://www.adafruit.com/products/757
\end_layout
\end_inset
.
I personally used this method while developing my software.
This shifter is specifically intended for use with I2C and has open drain
(open collector) outputs.
(It does not have 3-state outputs.) It should be fine for SPI provided you
keep the clock speed at around 400 kHz, the same speed I2C normally uses.
\end_layout
\begin_layout Itemize
The PCA9306 chip is designed as a robust I2C level shifter.
SparkFun sells breakout board
\begin_inset CommandInset href
LatexCommand href
name "BOB-10403"
target "http://www.sparkfun.com/products/10403"
\end_inset
\begin_inset Foot
status open
\begin_layout Plain Layout
http://www.sparkfun.com/products/10403
\end_layout
\end_inset
with this chip.
Caution: Check comments for BOB-10403 on the SparkFun web site.
Some people had problems with this board.
\end_layout
\begin_layout Subsection
A terrible level shifter
\end_layout
\begin_layout Standard
In Internet posts, some people have suggested using a diode in series to
level shift from 3.3 V to 5 V.
I checked this idea with my brother who is a professional electrical engineer
who designs digital ICs for a living.
He said this
\emph on
might
\emph default
work
\series bold
sometimes
\series default
for the SPI data pin (MISO) but will
\series bold
never
\series default
work for the interrupt pin.
He said the technique will only work if the signal changes state between
high and low very rapidly.
Depending on the data sent over the SPI bus, this may or may not happen.
However, because the interrupt line remains static most of the time, the
diode cannot raise the voltage of the radio's interrupt signal.
\end_layout
\begin_layout Section
Reliability of level shifted signals
\end_layout
\begin_layout Standard
When using the Si4735 shield with a 5 V Arduino, it is important that reliable
level shifting is used on the MISO SPI pin.
When an interrupt is received, the library sends a GET_INT_STATUS command
and then reads the status byte it returns.
If the MISO signal is unreliable, the interrupt code received by the Arduino
could be corrupted.
This could cause the library to falsely believe that an interrupt it was
waiting for has not yet arrived.
\end_layout
\begin_layout Standard
This problem will be most noticeable, if the STC (Seek\SpecialChar breakableslash
Tune Complete) interrupt
is missed after changing the radio's frequency.
In this case, the library will wait forever for the STC interrupt, despite
the fact the radio has sent it.
At this point, the only solution is manually pressing the Arduino's reset
button.
\end_layout
\begin_layout Standard
Another common symptom of an unreliable MISO connection is
\family sans
getFrequency()
\family default
or
\family sans
checkFrequency()
\family default
returning a bad frequency.
\end_layout
\begin_layout Standard
To help prevent this problem, I make the following recommendations:
\end_layout
\begin_layout Itemize
If possible, use a 3.3 V Arduino so no level shifting is required.
\end_layout
\begin_layout Itemize
If you must use a 5 V Arduino, use a robust level shifter.
\end_layout
\begin_layout Itemize
Keep the SPI bus frequency low.
The library's default frequency is very slow.
\end_layout
\begin_layout Itemize
Do not use a bread board with the level shifter.
All those metal strips inside the bread board pickup stray RF noise and
also slow down signals with stray capacitance.
\end_layout
\begin_layout Itemize
Keep any connecting wires as short as possible.
\end_layout
\begin_layout Itemize
Keep the radio's hardware away from your computer's fan and ventilation
holes and any other sources of RF noise.
While testing the library, I once placed the radio on top of a ventilation
hole in my computer's case.
The RF noise pouring out of this hole caused my radio to completely malfunction.
Once I moved the radio a few inches away, the radio began to work.
\end_layout
\begin_layout Itemize
Solder the connections, if possible.
If you are having problems with a signal and it's not soldered, try disconnecti
ng and then reconnecting its wires or try replacing its wires.
\end_layout
\begin_layout Itemize
Wrap the final hardware design in sheet metal to protect it from stray RF
noise.
However, make sure that any antennas are outside this shielding or you
will not receive any stations.
\end_layout
\begin_layout Section
Choosing which
\family sans
Si4735
\family default
class to use
\end_layout
\begin_layout Standard
To represent human readable text, RDS mostly uses a custom 8-bit character
set created by the European Broadcasting Union (EBU).
To make this received text easier to use, the library can optionally translate
the received EBU characters into either ASCII, Unicode, or the custom character
sets found in popular text mode display controllers.
Translation is controlled by choosing the correct class from those shown
in table
\begin_inset CommandInset ref
LatexCommand ref
reference "tab:Si4735-classes"
\end_inset
:
\end_layout
\begin_layout Standard
\begin_inset Float table
placement H
wide false
sideways false
status open
\begin_layout Plain Layout
\noindent
\align center
\begin_inset Tabular
<lyxtabular version="3" rows="5" columns="2">
<features tabularvalignment="middle">
<column alignment="left" valignment="top">
<column alignment="left" valignment="top">
<row>
<cell alignment="left" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
Class
\end_layout
\end_inset
</cell>
<cell alignment="left" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
Returned characters
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\family sans
Si4735
\end_layout
\end_inset
</cell>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
EBU (No translation)
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\family sans
Si4735_ASCII
\end_layout
\end_inset
</cell>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
ASCII
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\family sans
Si4735_HD44780_A00
\end_layout
\end_inset
</cell>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
HD44780 display controller, ROM character set A00
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\family sans
Si4735_HD44780_A02
\end_layout
\end_inset
</cell>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
HD44780 display controller, ROM character set A02
\end_layout
\end_inset
</cell>
</row>
</lyxtabular>
\end_inset
\end_layout
\begin_layout Plain Layout
\begin_inset Caption Standard
\begin_layout Plain Layout
\family sans
Si4735
\family default
classes
\begin_inset CommandInset label
LatexCommand label
name "tab:Si4735-classes"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\family sans
Si4735
\family default
is the base class and does no translating.
To translate EBU characters into Unicode characters, use the
\family sans
Si4735
\family default
class.
You must then manually translate each EBU character received by calling
either
\family sans
EBUToUCS2()
\family default
or
\family sans
EBUToUTF8()
\family default
.
Every EBU character has an exact Unicode equivalent.
\end_layout
\begin_layout Description
Note: The original
\family sans
Si4735
\family default
base class always did a primitive ASCII translation.
Old applications may want to change to the
\family sans
Si4735_ASCII
\family default
class.
\end_layout
\begin_layout Standard
The
\family sans
Si4735_ASCII
\family default
derived class translates all received characters into ASCII characters.
This translation should work with almost any text output device, but, its
translations have the worst quality.
\end_layout
\begin_layout Standard
The
\family sans
Si4735_HD44780_A00
\family default
and
\family sans
Si4735_HD44780_A02
\family default
derived classes work with both the HD44780 and ST7066 controller chips,
commonly found in text mode displays.
This includes LCDs, OLEDs, VFDs, etc.
They will not work with graphic mode displays designed to show pictures
and other fancy graphics.
\end_layout
\begin_layout Standard
The
\family sans
Si4735_HD44780_A00
\family default
derived class translates all received characters into the custom character
set used by most display controllers.
The HD44780 controller should have ROM character set A00 and the ST7066
controller should have ROM character set 0A.
All text displays (LCD, etc.) available to hobbyists will use this character
set and will therefore work with this class.
\end_layout
\begin_layout Standard
The
\family sans
Si4735_HD44780_A02
\family default
derived class translates all received characters into a custom character
set rarely used by display controllers.
The HD44780 controller should have ROM character set A02.
This character set gives better translations for less commonly used EBU
characters, but displays using this controller are impossible for hobbyists
to find.
\end_layout
\begin_layout Standard
If you do not know which class to use for your text mode display controller,
try
\family sans
Si4735_HD44780_A00
\family default
.
\end_layout
\begin_layout Standard
When the derived classes translate EBU characters, they sometimes do not
have an exact match in the target character set.
In this case, characters are either transliterated or, as recommended by
the RDS standard, a space is substituted.
\end_layout
\begin_layout Description
Note: Throughout this library's documentation and source code, any reference
to the
\family sans
Si4735
\family default
base class applies to all derived classes unless otherwise indicated.
\end_layout
\begin_layout Section
\begin_inset CommandInset label
LatexCommand label
name "sec:Initializing-the-radio"
\end_inset
Initializing the radio and library and setting the receive band
\end_layout
\begin_layout Standard
You must call
\family sans
begin()
\family default
to initialize this library before calling any other methods.
When called, it initializes the SPI or I2C bus.
Because you may wish to do this yourself or with another library, you may
tell
\family sans
begin()
\family default
to skip initializing these buses by calling
\family sans
begin(BEGIN_DO_NOT_INIT_BUS)
\family default
.
\end_layout
\begin_layout Standard
The second argument to
\family sans
begin()
\family default
is the bus argument.
For SPI, it gives the clock divider to pass to
\family sans
SPIClass :: setClockDivider()
\family default
.
If no bus argument is given to
\family sans
begin()
\family default
,
\family sans
RADIO_SPI_CLOCK_DIV
\family default
in
\family sans
Si4735.h
\family default
is used.
\end_layout
\begin_layout Standard
Example code to set the SPI bus clock to divide by 8.
On a 16 MHz Arduino, this will set the SPI clock to
\begin_inset Formula $16\textrm{ MHz}\div8=2\textrm{ MHz}$
\end_inset
:
\end_layout
\begin_layout LyX-Code
begin(BEGIN_DEFAULT, SPI_CLOCK_DIV8);
\end_layout
\begin_layout Standard
For I2C, the bus argument gives the address of the radio.
The radio will respond to one of two I2C addresses.
The address used by the radio is selected by the signal given to the radio's
SEN\SpecialChar breakableslash
SS pin.
The following table gives the possible addresses:
\end_layout
\begin_layout Quote
\begin_inset Tabular
<lyxtabular version="3" rows="3" columns="2">
<features tabularvalignment="middle">
<column alignment="left" valignment="top">
<column alignment="center" valignment="top">
<row>
<cell alignment="left" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
I2C bus argument for
\family sans
begin()
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" bottomline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
SEN pin
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\family sans
RADIO_I2C_ADDRESS_HIGH
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
HIGH
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="left" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\family sans
RADIO_I2C_ADDRESS_LOW
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
LOW
\end_layout
\end_inset
</cell>
</row>
</lyxtabular>
\end_inset
\end_layout
\begin_layout Standard
If no bus argument is given,
\family sans
RADIO_I2C_ADDRESS
\family default
in
\family sans
Si4735.h
\family default
is used.
By default,
\family sans
RADIO_I2C_ADDRESS
\family default
equals
\family sans
RADIO_I2C_ADDRESS_HIGH
\family default
.
Note that the Si4707 breakout board has a 10 k
\begin_inset Formula $\Omega$
\end_inset
pull-up resistor connected to SEN to make it go high.
\end_layout
\begin_layout Standard
Example code to set the I2C address to its low value:
\end_layout
\begin_layout LyX-Code
begin(BEGIN_DEFAULT, RADIO_I2C_ADDRESS_LOW);
\end_layout
\begin_layout Standard
The radio has a low power
\begin_inset Quotes eld
\end_inset
off
\begin_inset Quotes erd
\end_inset
mode and modes for each receive band.
After calling
\family sans
begin()
\family default
, the radio is in the low power
\family sans
RADIO_OFF
\family default
mode.
You change the radio's mode by calling
\family sans
setMode()
\family default
.
For example, calling
\family sans
setMode(FM)
\family default
powers up the radio and sets the receive mode to the FM band.
See
\family sans
Si4735.h
\family default
for a list of all supported modes.
\end_layout
\begin_layout Standard
The radio's current mode is returned by
\family sans
getMode()
\family default
.
\end_layout
\begin_layout Standard
By calling
\family sans
setMode(RADIO_OFF)
\family default
, the radio goes back into low power mode.
To kill all power to the radio, call
\family sans
end()
\family default
.
To restore power later, call
\family sans
begin()
\family default
.
\end_layout
\begin_layout Standard
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
use_makebox 0
width "100col%"
special "none"
height "1in"
height_special "totalheight"
thickness "0.4pt"
separation "3pt"
shadowsize "4pt"
framecolor "black"
backgroundcolor "none"
status open
\begin_layout Description
\series bold
Warning: Unlike previous versions of this library from other people,
\family sans
begin()
\family default
does
\bar under
not
\bar default
set the receive band.
Call
\family sans
setMode()
\family default
to do this.
\series default
As a result, the following code fragment:
\end_layout
\begin_deeper
\begin_layout LyX-Code
radio.begin(FM);
\end_layout
\begin_layout Plain Layout
should be changed to:
\end_layout
\begin_layout LyX-Code
radio.begin();
\end_layout
\begin_layout LyX-Code
radio.setMode(FM);
\end_layout
\begin_layout Plain Layout
Open the
\family sans
Changes.text
\family default
file in a programmer's text editor to see why this change was made.
\end_layout
\end_deeper
\end_inset
\end_layout
\begin_layout Standard
\family sans
setMode()
\family default
sets up the given band's top and bottom frequency and its spacing based
on the previously set locale.
(See
\begin_inset CommandInset ref
LatexCommand formatted
reference "sec:Localization"
\end_inset
\begin_inset Quotes eld
\end_inset
\begin_inset CommandInset ref
LatexCommand nameref
reference "sec:Localization"
\end_inset
.
\begin_inset Quotes erd
\end_inset
) You may override these band settings by calling
\family sans
setBandTop()
\family default
,
\family sans
setBandBottom()
\family default
, and
\family sans
setSpacing()
\family default
after calling
\family sans
setMode()
\family default
.
To get the current band settings, call
\family sans
getBandTop()
\family default
,
\family sans
getBandBottom()
\family default
, and
\family sans
getSpacing()
\family default
.
\end_layout
\begin_layout Standard
There are a small number of differences between the Si4735-C40 and Si4735-D60.
As a result,
\family sans
setMode()
\family default
sends the GET_REV command to the radio and saves the results in the
\family sans
revision
\family default
structure, located in the public part of the
\family sans
Si4735
\family default
class structure.
This permits your software and this library to determine which chip is
being used and adapt themselves to it.
For a list of differences and compatibly concerns, see Appendix A and B
in the
\begin_inset Quotes eld
\end_inset
Si47xx Programming Guide.
\begin_inset Quotes erd
\end_inset
(Please note that the audio noise bug in FM receive mode documented in
Appendix B is corrected by this library.)
\end_layout
\begin_layout Section
Using the library with or without interrupts
\end_layout
\begin_layout Standard
Previous versions of this library from other people did not support receiving
interrupt signals from the radio chip.
Instead, the library and application would poll the radio to see if some
event had occurred yet.
This approach causes a large amount of bus traffic between the Arduino
and radio chips.
This is undesirable because bus traffic can introduce noise into the radio
chip which can be heard in the audio output.
Also, the manuals say that bus traffic can harm tuning operations when
using an external crystal connected to the RCLK and GPO3 pins with the
radio chip's internal oscillator circuit.
(Please note that the Si4735 shield uses this setup, and therefore, shield
users should avoid any bus traffic while tuning a new station.)
\end_layout
\begin_layout Standard
This library supports waiting for an interrupt signal from the radio chip
before asking it what event has taken place.
Or, you can choose to poll the radio at any time.
\end_layout
\begin_layout Standard
The library automatically tells the radio to send STC (Seek\SpecialChar breakableslash
Tune Complete),
RDS (Radio Data System), and RSQ (Received Signal Quality) interrupts.
\end_layout
\begin_layout Standard
To keep the design simple, the library does not use a complex interrupt
handler.
Instead we just poll the AVR's interrupt registers to see when an interrupt
pulse has been received from the radio chip.
On ARM based Arduinos, a short interrupt handler sets a flag variable and
then returns.
Later, the library polls this flag variable to check for interrupts.
\end_layout
\begin_layout Subsection
Tuning
\end_layout
\begin_layout Standard
To change to a particular frequency, call
\family sans
tuneFrequency()
\family default
.
To increment or decrement the current frequency, call
\family sans
frequencyUp()
\family default
or
\family sans
frequencyDown()
\family default
.
\end_layout
\begin_layout Standard
To seek to the next or previous frequency, call
\family sans
seekUp()
\family default
or
\family sans
seekDown()
\family default
.
To cancel a seek operation call
\family sans
cancelSeek()
\family default
.
\end_layout
\begin_layout Standard
To manually ask the radio if a seek or tune operation has completed, call
\family sans
getFrequency()
\family default
.
It immediately asks the radio if tuning is complete and, if so, its current
frequency.
\family sans
checkFrequency()
\family default
works the same but only asks the radio if the STC interrupt has been received.
\end_layout
\begin_layout Standard
\family sans
currentFrequency()
\family default
returns the radio's current frequency or
\family sans
0
\family default
if unknown.
(The frequency is usually unknown because a seek operation is underway.)
Note:
\family sans
currentFrequency()
\family default
does not indicate if the previous tune or seek operation has completed.
It only returns the frequency from the last tune operation or call to
\family sans
getFrequency()
\family default
or
\family sans
checkFrequency()
\family default
.
\end_layout
\begin_layout Standard
Calling
\family sans
waitSTC()
\family default
will not return until the STC interrupt has been received.
This is useful after calling
\family sans
tuneFrequency()
\family default
,
\family sans
frequencyUp()
\family default
,
\family sans
frequencyDown()
\family default
,
\family sans
seekUp()
\family default
, or
\family sans
seekDown()
\family default
.
\end_layout
\begin_layout Standard
Methods
\family sans
tuneFrequencyAndWait()
\family default
,
\family sans
frequencyUpAndWait()
\family default
, and
\family sans
frequencyDownAndWait()
\family default
automatically call
\family sans
waitSTC()
\family default
after changing the frequency.
\end_layout
\begin_layout Description
Note: Seeking on some bands (like SW) can take a long time to find a station.
Therefore, it is recommended that the application using this library handle
seeks in the following way.
First, call
\family sans
seekUp()
\family default
or
\family sans
seekDown()
\family default
.
Second, enter a loop which looks for two events: either the user wants
to cancel the seek or the STC interrupt has been received because the seek
has finished.
The following incomplete code fragment shows how to do this:
\end_layout
\begin_deeper
\begin_layout LyX-Code
radio.seekUp();
\end_layout
\begin_layout LyX-Code
word station;
\end_layout
\begin_layout LyX-Code
bool user_cancel_seek=false;
\end_layout
\begin_layout LyX-Code
do{
\end_layout
\begin_layout LyX-Code
//add code here to see if user wants to cancel seek
\end_layout
\begin_layout LyX-Code
\end_layout
\begin_layout LyX-Code
if(user_cancel_seek == true){
\end_layout
\begin_layout LyX-Code
station = radio.cancelSeek();
\end_layout
\begin_layout LyX-Code
break;
\end_layout
\begin_layout LyX-Code
}
\end_layout
\begin_layout LyX-Code
//check if seek finished, that is, STC interrupt received
\end_layout
\begin_layout LyX-Code
station = radio.checkFrequency();
\end_layout
\begin_layout LyX-Code
}while(station == 0);
\end_layout
\end_deeper
\begin_layout Subsection
RDS
\end_layout
\begin_layout Standard
There are two methods for reading RDS data,
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getRDS()
\family default
and
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checkRDS()
\family default
.
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getRDS()
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immediately asks the radio to send any RDS data by sending an FM_RDS_STATUS
command.
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checkRDS()
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first checks if an RDS interrupt has been received.
If so,
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checkRDS()
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calls
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getRDS()
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.
Otherwise
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checkRDS()
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returns immediately.
RDS data is stored inside the
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rds
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structure, located in the public part of the
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Si4735
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class structure.
\end_layout
\begin_layout Standard
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getCallSign()
\family default
translates an RBDS (USA) PI code into the station's call letters.
Note, this works for US stations because their PI codes are based on their
call letters.
In other countries, PI codes are arbitrarily assigned.
We would need to create a large database matching PI codes to station IDs.
\end_layout
\begin_layout Standard
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getProgramTypeStr()
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translates the ProgramType code into an English message.
Works for both RDS and RBDS.
\end_layout
\begin_layout Standard
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getLocalTime()
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and
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getLocalDateTime()
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return the local time returned by the station.
\end_layout
\begin_layout Subsection
RSQ
\end_layout
\begin_layout Standard
There are two methods for reading RSQ information,
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getRSQ()
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and
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checkRSQ()
\family default
.
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getRSQ()
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immediately asks the radio for the current RSQ information by sending an
RSQ_STATUS command.
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checkRSQ()
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first checks if an RSQ interrupt has been received.
If so,
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checkRSQ()
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calls
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getRSQ()
\family default
.
Otherwise
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checkRSQ()
\family default
returns immediately.
\end_layout
\begin_layout Standard
The RSQ interrupt is sent by the radio when certain thresholds have occurred.
These thresholds are configured by setting properties with the
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setProperty()
\family default
method.
For FM, these properties include:
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_INT_SOURCE
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_SNR_HI_THRESHOLD
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_SNR_LO_THRESHOLD
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_RSSI_HI_THRESHOLD
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_RSSI_LO_THRESHOLD
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_MULTIPATH_HI_THRESHOLD (Not on Si4735-C40)
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_MULTIPATH_LO_THRESHOLD (Not on Si4735-C40)
\end_layout
\begin_layout LyX-Code
PROP_FM_RSQ_BLEND_THRESHOLD
\end_layout
\begin_layout Standard
AM has similar properties.
Not all properties are supported by all chips.
See the “Si47xx Programming Guide
\begin_inset Quotes erd
\end_inset
for more information on these properties.
\end_layout
\begin_layout Subsection
Manually reading interrupts
\end_layout
\begin_layout Standard
You may manually ask the radio what interrupts have been sent by calling
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getInterrupts()
\family default
.
This sends a GET_INT_STATUS command to the radio, saves the result internally,
and then returns the result.
\end_layout
\begin_layout Standard
Also, you may call
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currentInterrupts()
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to ask the library what interrupts have been received.
If a new interrupt signal has been received by the Arduino,
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currentInterrupts()
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calls
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getInterrupts()
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.
If no new interrupt signal has been received,
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currentInterrupts()
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returns the previously saved interrupt status.
\end_layout
\begin_layout Section
\begin_inset CommandInset label
LatexCommand label
name "sec:Localization"
\end_inset
Localization
\end_layout
\begin_layout Standard
Localization is done in two parts: an ITU region and a locale within that
region.
Both are set by calling
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setRegionAndLocale()
\family default
.
\end_layout
\begin_layout Standard
The ITU (International Telecommunication Union) has divided the world into
3 regions.
For the most part, radio broadcasting is the same throughout each region.
In some cases, the library subdivides regions into subregions.
To handle exceptions within each region or subregion, you may also set
a locale.
\end_layout
\begin_layout Standard
For example, the USA is in region 2, subregion North America.
However, unlike other countries, it uses RBDS instead of RDS.
Therefore, the USA has a separate locale.
To setup the library for the USA:
\end_layout
\begin_layout LyX-Code
radio.setRegionAndLocale(REGION_2_NA, LOCALE_US);
\end_layout
\begin_layout Standard
Please note that the library defaults to the USA.
\end_layout
\begin_layout Standard
For locations that do not need localization beyond specifying their region
and subregion, a special locale code is used:
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LOCALE_OTHER
\family default
.
For example, most of Europe should work by calling:
\end_layout
\begin_layout LyX-Code
radio.setRegionAndLocale(REGION_1, LOCALE_OTHER);
\end_layout
\begin_layout Standard
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setRegionAndLocale()
\family default
should only be called while the radio is in the low power
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RADIO_OFF
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mode.
\end_layout
\begin_layout Standard
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getRegion()
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returns the current region and subregion code.
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getLocale()
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returns the current locale code for the current region and subregion.
\end_layout
\begin_layout Standard
See the
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Si4735.h
\family default
file for the list of region and locale constants and more information on
their use.
\end_layout
\begin_layout Section
Volume
\end_layout
\begin_layout Standard
The volume can be changed by calling
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volumeUp()
\family default
or
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volumeDown()
\family default
.
Both methods take an argument giving the amount to increase or decrease
the volume.
Also, you can set the volume to a given value by calling
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setVolume()
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.
All three methods return the new volume setting.
To read the current volume setting at any time, call
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getVolume()
\family default
.
\end_layout
\begin_layout Standard
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mute()
\family default
and
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unmute()
\family default
activate or deactivate muting.
You can also toggle mute by calling
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toggleMute()
\family default
.
It then returns the new mute status.
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getMute()
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returns true if mute is currently active.
\end_layout
\begin_layout Standard
The volume and mute methods can be called while the radio is powered up
in a receive mode or the radio is in the low power
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RADIO_OFF
\family default
mode.
\end_layout
\begin_layout Section
Sending commands to the radio
\end_layout
\begin_layout Standard
\noindent
The most useful commands already have library methods.
However, you may choose to manually send commands to the radio by calling
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sendCommand()
\family default
or
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sendCommand_P()
\family default
.
To get the results, call
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getStatus()
\family default
for the single byte status code or
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getResponse()
\family default
for the longer 16 byte response.
For your convenience, predefined command codes can be found in
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Si4735.h
\family default
.
\end_layout
\begin_layout Standard
Many features are controlled with properties.
Call
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setProperty()
\family default
to set a property and
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getProperty()
\family default
to read its current value.
For your convenience, predefined property codes can be found in
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Si4735.h
\family default
.
\end_layout
\end_body
\end_document
