gumstix

Hi John,

> I have a connex 400xm and gpsstix board connected together, and was
> hoping to be able to connect to the robostix over the i2c to be able to
> read the adc's and control a couple of servos. Is the I2C broken out on
> the robostix anywhere other than the hirose? I assume I'd have to
> connect the I2C1-4 pins on the gpsstix board to 4 I2C pins on the
> robostix, I'm just not sure which ones they are. Thanks in advance.

You have a couple of options:

1 - The 3.3v to 5v converter for the robostix is the 8 pin chip that's
closest to the hirose connector (and has 9515A printed on it). Pin 2
is the 3.3v SCL, and pin 3 is the 3.3v SDA (Pin 1 is in the corner
with the dot). You could solder wires onto there.

2 - The 5v SCL and SDA lines are available on the UARTS connector. Pin
12 is SDA and pin 16 is SCL. These are connected to +5 through a
pullup resistor. If you were to connect a 20k resistor between each
pin and ground, you should be able to connect the lines directly to
the gumstix. I haven't tested this....

3 - You could use an external voltage converter to convert the +5 to 3.3v

4 - You could opt to use a different ATMega processor, like the
ATMega8L, which is available in a DIP package. You could run the
ATMega8L at 3.3v

5 - Similar to 4, but run it at 5v but pullup the SDA and SCL to 3.3v
and connect them up directly to the gumstix.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

Thanks for the reply Dave,

I think I'll go for one of the first two since I can do it with 
everything I have here. So it's only the SDA and SCL lines that need to 
be connected, do the two boards need to share a ground also?  And this 
might be a silly question but is the wiring,

sda > sda
scl > scl

or

sda > scl
scl > sda

Thanks again,

    -Jon



Dave Hylands wrote:
> Hi John,
>
>   
>> I have a connex 400xm and gpsstix board connected together, and was
>> hoping to be able to connect to the robostix over the i2c to be able to
>> read the adc's and control a couple of servos. Is the I2C broken out on
>> the robostix anywhere other than the hirose? I assume I'd have to
>> connect the I2C1-4 pins on the gpsstix board to 4 I2C pins on the
>> robostix, I'm just not sure which ones they are. Thanks in advance.
>>     
>
> You have a couple of options:
>
> 1 - The 3.3v to 5v converter for the robostix is the 8 pin chip that's
> closest to the hirose connector (and has 9515A printed on it). Pin 2
> is the 3.3v SCL, and pin 3 is the 3.3v SDA (Pin 1 is in the corner
> with the dot). You could solder wires onto there.
>
> 2 - The 5v SCL and SDA lines are available on the UARTS connector. Pin
> 12 is SDA and pin 16 is SCL. These are connected to +5 through a
> pullup resistor. If you were to connect a 20k resistor between each
> pin and ground, you should be able to connect the lines directly to
> the gumstix. I haven't tested this....
>
> 3 - You could use an external voltage converter to convert the +5 to 3.3v
>
> 4 - You could opt to use a different ATMega processor, like the
> ATMega8L, which is available in a DIP package. You could run the
> ATMega8L at 3.3v
>
> 5 - Similar to 4, but run it at 5v but pullup the SDA and SCL to 3.3v
> and connect them up directly to the gumstix.
>
>

Hi Jon,

On 6/9/06, Jon Keller <jon@...> wrote:
> Thanks for the reply Dave,
>
> I think I'll go for one of the first two since I can do it with
> everything I have here. So it's only the SDA and SCL lines that need to
> be connected, do the two boards need to share a ground also?  And this
> might be a silly question but is the wiring,

Yes you need a common ground as well.

> sda > sda
> scl > scl

That's the correct way.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

I'm giving number 2 a try first since its the quickest, I've cabled this 
all up and booted both boards. I've load all the correct i2c modules, 
however when I run the 'i2c-io 0x0b info' command I get the error,

# ./i2c-io 0x0b info
ERROR: I2cTransfer: ioctl failed: Remote I/O error (121)
ERROR: I2cReadBlock failed
ERROR: Unable to retrieve information from i2c address 0x0b

This error also shows up in the syslog at the same time,

Dec 31 16:26:59 gumstix user.warn kernel: i2c: error: exhausted retries
Dec 31 16:26:59 gumstix user.warn kernel: i2c: msg_num: 0 msg_idx: -2000 
msg_ptr: 0
Dec 31 16:26:59 gumstix user.warn kernel: i2c: ICR: 000007e0 ISR: 00000002
Dec 31 16:26:59 gumstix user.warn kernel: i2c: log: [00000446:000007e0]

The red light on the robostix is blinking twice per second so I'd say 
the right program is running

I connected pin12 on the robostix to the sda pin on the gpsstix with a 
20k resister in between, and pin 16 on the robostix to the scl on the 
gpsstix, also with the resister.

Since this hasn't been tested I wont spend too much time trying to get 
it to work, but maybe I've made an obvious mistake I can't yet see.


    -Jon



Dave Hylands wrote:
> Hi John,
>
>   
>> I have a connex 400xm and gpsstix board connected together, and was
>> hoping to be able to connect to the robostix over the i2c to be able to
>> read the adc's and control a couple of servos. Is the I2C broken out on
>> the robostix anywhere other than the hirose? I assume I'd have to
>> connect the I2C1-4 pins on the gpsstix board to 4 I2C pins on the
>> robostix, I'm just not sure which ones they are. Thanks in advance.
>>     
>
> You have a couple of options:
>
> 1 - The 3.3v to 5v converter for the robostix is the 8 pin chip that's
> closest to the hirose connector (and has 9515A printed on it). Pin 2
> is the 3.3v SCL, and pin 3 is the 3.3v SDA (Pin 1 is in the corner
> with the dot). You could solder wires onto there.
>
> 2 - The 5v SCL and SDA lines are available on the UARTS connector. Pin
> 12 is SDA and pin 16 is SCL. These are connected to +5 through a
> pullup resistor. If you were to connect a 20k resistor between each
> pin and ground, you should be able to connect the lines directly to
> the gumstix. I haven't tested this....
>
> 3 - You could use an external voltage converter to convert the +5 to 3.3v
>
> 4 - You could opt to use a different ATMega processor, like the
> ATMega8L, which is available in a DIP package. You could run the
> ATMega8L at 3.3v
>
> 5 - Similar to 4, but run it at 5v but pullup the SDA and SCL to 3.3v
> and connect them up directly to the gumstix.
>
>

I removed my resisters and soldered straight to the 5v > 3.3v converters 
pins...they are pretty darn tiny but i managed to get them on there..its 
all working now :)

    -Jon

Jon Keller wrote:
> I'm giving number 2 a try first since its the quickest, I've cabled this 
> all up and booted both boards. I've load all the correct i2c modules, 
> however when I run the 'i2c-io 0x0b info' command I get the error,
>
> # ./i2c-io 0x0b info
> ERROR: I2cTransfer: ioctl failed: Remote I/O error (121)
> ERROR: I2cReadBlock failed
> ERROR: Unable to retrieve information from i2c address 0x0b
>
> This error also shows up in the syslog at the same time,
>
> Dec 31 16:26:59 gumstix user.warn kernel: i2c: error: exhausted retries
> Dec 31 16:26:59 gumstix user.warn kernel: i2c: msg_num: 0 msg_idx: -2000 
> msg_ptr: 0
> Dec 31 16:26:59 gumstix user.warn kernel: i2c: ICR: 000007e0 ISR: 00000002
> Dec 31 16:26:59 gumstix user.warn kernel: i2c: log: [00000446:000007e0]
>
> The red light on the robostix is blinking twice per second so I'd say 
> the right program is running
>
> I connected pin12 on the robostix to the sda pin on the gpsstix with a 
> 20k resister in between, and pin 16 on the robostix to the scl on the 
> gpsstix, also with the resister.
>
> Since this hasn't been tested I wont spend too much time trying to get 
> it to work, but maybe I've made an obvious mistake I can't yet see.
>
>
>     -Jon
>
>
>
> Dave Hylands wrote:
>   
>> Hi John,
>>
>>   
>>     
>>> I have a connex 400xm and gpsstix board connected together, and was
>>> hoping to be able to connect to the robostix over the i2c to be able to
>>> read the adc's and control a couple of servos. Is the I2C broken out on
>>> the robostix anywhere other than the hirose? I assume I'd have to
>>> connect the I2C1-4 pins on the gpsstix board to 4 I2C pins on the
>>> robostix, I'm just not sure which ones they are. Thanks in advance.
>>>     
>>>       
>> You have a couple of options:
>>
>> 1 - The 3.3v to 5v converter for the robostix is the 8 pin chip that's
>> closest to the hirose connector (and has 9515A printed on it). Pin 2
>> is the 3.3v SCL, and pin 3 is the 3.3v SDA (Pin 1 is in the corner
>> with the dot). You could solder wires onto there.
>>
>> 2 - The 5v SCL and SDA lines are available on the UARTS connector. Pin
>> 12 is SDA and pin 16 is SCL. These are connected to +5 through a
>> pullup resistor. If you were to connect a 20k resistor between each
>> pin and ground, you should be able to connect the lines directly to
>> the gumstix. I haven't tested this....
>>
>> 3 - You could use an external voltage converter to convert the +5 to 3.3v
>>
>> 4 - You could opt to use a different ATMega processor, like the
>> ATMega8L, which is available in a DIP package. You could run the
>> ATMega8L at 3.3v
>>
>> 5 - Similar to 4, but run it at 5v but pullup the SDA and SCL to 3.3v
>> and connect them up directly to the gumstix.
>>
>>   
>>     
>
>
>
> _______________________________________________
> gumstix-users mailing list
> gumstix-users@...
> https://lists.sourceforge.net/lists/listinfo/gumstix-users
>

Hi Jon,

> I connected pin12 on the robostix to the sda pin on the gpsstix with a
> 20k resister in between, and pin 16 on the robostix to the scl on the
> gpsstix, also with the resister.
>
> Since this hasn't been tested I wont spend too much time trying to get
> it to work, but maybe I've made an obvious mistake I can't yet see.

I see from a later email that you got things working, but I figured
I'd answer this anyways.

You needed to connect the 20k resistor between SDA and ground, and
another between SCL and ground, and then connect the SDA and SCL pins
to the gpsstix.

This would basically create a resistor divider network with the 10k
resistor already between each of those pins and +5, effectively
pullingup SDA and SCL to 3.33v

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

Oh I see, you did in fact that that in your email as well, I just 
mis-read it.

I'll still give this a try since this i2c connection is quite critical 
and these tiny solders don't take much to break. I'd much rather get it 
connected through the pins.

Thanks Dave

    -Jon



Dave Hylands wrote:
> Hi Jon,
>
>   
>> I connected pin12 on the robostix to the sda pin on the gpsstix with a
>> 20k resister in between, and pin 16 on the robostix to the scl on the
>> gpsstix, also with the resister.
>>
>> Since this hasn't been tested I wont spend too much time trying to get
>> it to work, but maybe I've made an obvious mistake I can't yet see.
>>     
>
> I see from a later email that you got things working, but I figured
> I'd answer this anyways.
>
> You needed to connect the 20k resistor between SDA and ground, and
> another between SCL and ground, and then connect the SDA and SCL pins
> to the gpsstix.
>
> This would basically create a resistor divider network with the 10k
> resistor already between each of those pins and +5, effectively
> pullingup SDA and SCL to 3.33v
>
>

I rewired it all following the instructions below, I wired to the bottom 
of the headers pins, the sda and scl headers both had grounds right next 
to each so I used those. Still seem to be getting the same error though.

Are each of these pins bi-directional? On the board they are labeled tx 
and rx. If they weren't bi-directional would adding the 20k resister to 
an already 3.3v coming from the gpsstix drop it even more? Maybe I'm way 
off, but I still get the "gumstix user.warn kernel: i2c: error: 
exhausted retries" error.

    -Jon

Dave Hylands wrote:
> Hi Jon,
>
>   
>> I connected pin12 on the robostix to the sda pin on the gpsstix with a
>> 20k resister in between, and pin 16 on the robostix to the scl on the
>> gpsstix, also with the resister.
>>
>> Since this hasn't been tested I wont spend too much time trying to get
>> it to work, but maybe I've made an obvious mistake I can't yet see.
>>     
>
> I see from a later email that you got things working, but I figured
> I'd answer this anyways.
>
> You needed to connect the 20k resistor between SDA and ground, and
> another between SCL and ground, and then connect the SDA and SCL pins
> to the gpsstix.
>
> This would basically create a resistor divider network with the 10k
> resistor already between each of those pins and +5, effectively
> pullingup SDA and SCL to 3.33v
>
>

Hi Jon,

On 6/20/06, Jon Keller <jon@...> wrote:
> I rewired it all following the instructions below, I wired to the bottom
> of the headers pins, the sda and scl headers both had grounds right next
> to each so I used those. Still seem to be getting the same error though.
>
> Are each of these pins bi-directional? On the board they are labeled tx
> and rx. If they weren't bi-directional would adding the 20k resister to
> an already 3.3v coming from the gpsstix drop it even more? Maybe I'm way
> off, but I still get the "gumstix user.warn kernel: i2c: error:
> exhausted retries" error.

Yes, both pins are bidirectional. The Tx and Rx pins are misnomers.

Pin 12 is SDA, and pin 16 is SCL. They're both 5v logic levels and
have 10k pullups to +5.

The problem is that the gumstix can only tolerate 3.3v, so my idea was
to add the 20k to get the pullups to drop to 3.3v.

Did you connect the grounds up between the robostix and the gpsstix?

You should measure 3,3v on the robostix SDA and SCL lines with the 20k
resistors in place.

I'll see if I can get something working here....

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

Thanks Dave,

I re-checked my ground, I had my ground wire going from the gpsstix to 
pin 2 of the uarts on the robostix which is labeled G. When I checked 
with the multimeter the voltage seemed to be bouncing around all over 
the place between 0 and 3.3ish, so I moved my shared ground wire to one 
of the grounds on the pwm ports. The voltage is now stable and the i2c 
is now working. I'm not too sure why it didn't work on the other ground 
pin, unless pin2 isn't a ground at all?

    -Jon

Dave Hylands wrote:
> Hi Jon,
>
> On 6/20/06, Jon Keller <jon@...> wrote:
>   
>> I rewired it all following the instructions below, I wired to the bottom
>> of the headers pins, the sda and scl headers both had grounds right next
>> to each so I used those. Still seem to be getting the same error though.
>>
>> Are each of these pins bi-directional? On the board they are labeled tx
>> and rx. If they weren't bi-directional would adding the 20k resister to
>> an already 3.3v coming from the gpsstix drop it even more? Maybe I'm way
>> off, but I still get the "gumstix user.warn kernel: i2c: error:
>> exhausted retries" error.
>>     
>
> Yes, both pins are bidirectional. The Tx and Rx pins are misnomers.
>
> Pin 12 is SDA, and pin 16 is SCL. They're both 5v logic levels and
> have 10k pullups to +5.
>
> The problem is that the gumstix can only tolerate 3.3v, so my idea was
> to add the 20k to get the pullups to drop to 3.3v.
>
> Did you connect the grounds up between the robostix and the gpsstix?
>
> You should measure 3,3v on the robostix SDA and SCL lines with the 20k
> resistors in place.
>
> I'll see if I can get something working here....
>
>

Hi Jon,

> I re-checked my ground, I had my ground wire going from the gpsstix to
> pin 2 of the uarts on the robostix which is labeled G. When I checked
> with the multimeter the voltage seemed to be bouncing around all over
> the place between 0 and 3.3ish, so I moved my shared ground wire to one
> of the grounds on the pwm ports. The voltage is now stable and the i2c
> is now working. I'm not too sure why it didn't work on the other ground
> pin, unless pin2 isn't a ground at all?

Yeah - pin 2 is supposed to be ground, and it's connected to a piece
of ground plane. But if you hold your board up to the light, you can
see that that little piece of ground plane doesn't actually go
anywhere.

All of the other pins that are labelled G are fine. I recommend
soldering a small wire on the back of the robostix to rememdy this.

I added a note about this somewhere, but I just added another note on
the Robostix schematic page as well.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

Hi Jon,

> > I re-checked my ground, I had my ground wire going from the gpsstix to
> > pin 2 of the uarts on the robostix which is labeled G. When I checked
> > with the multimeter the voltage seemed to be bouncing around all over
> > the place between 0 and 3.3ish, so I moved my shared ground wire to one
> > of the grounds on the pwm ports. The voltage is now stable and the i2c
> > is now working. I'm not too sure why it didn't work on the other ground
> > pin, unless pin2 isn't a ground at all?

And just to double check - you got it working with the 20k resistors?
If so, that's good to know.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

Yup once I moved the ground away from that pin it starting working 
perfectly. I'm reading my sensors and controlling the servos with only 
the 3 cables connecting the boards. Thanks again :D

    -Jon



Dave Hylands wrote:
> Hi Jon,
>
>   
>>> I re-checked my ground, I had my ground wire going from the gpsstix to
>>> pin 2 of the uarts on the robostix which is labeled G. When I checked
>>> with the multimeter the voltage seemed to be bouncing around all over
>>> the place between 0 and 3.3ish, so I moved my shared ground wire to one
>>> of the grounds on the pwm ports. The voltage is now stable and the i2c
>>> is now working. I'm not too sure why it didn't work on the other ground
>>> pin, unless pin2 isn't a ground at all?
>>>       
>
> And just to double check - you got it working with the 20k resistors?
> If so, that's good to know.
>
>

Have a side question about I2C with the Robostix.
If i wanted to throw on another I2C analog to Digital Converter (not for 
robot sensor purposes but to check battery power and current so I could 
initiate a shutdown/hybernate mode for my robot, I was thinking an ADS7828) 
Could I get the Gumstix to read that off of the I2C header on the robostix?

The reason I would want to use this is beause I'm going to be using most of 
the A/D on the robostix for actual robot sensors(Sharp IR's and some IMU's 
from Spark Fun).

>From this diagram It seems possible to me but I'd thought I'd ask and look 
before I leap
(I'm no EE guy so this kind of board diagram confuses me)
Diagram: http://www.davehylands.com/gumstix-wiki/robostix-block.png

And I'm just a bit confused about what was going on with the GPSStix with 
the other (20k) resistors but, are the pullup resistors already on the board 
or would I have to add them for the SCL and SDA if I used the Headers on the 
RoboStix?



>From: "Dave Hylands" <dhylands@...>
>Reply-To: "General mailing list for gumstix users." 
><gumstix-users@...>
>To: "General mailing list for gumstix users." 
><gumstix-users@...>
>Subject: Re: [Gumstix-users] robostix and gpsstix I2C
>Date: Wed, 21 Jun 2006 00:20:29 -0700
>
>Hi Jon,
>
> > > I re-checked my ground, I had my ground wire going from the gpsstix to
> > > pin 2 of the uarts on the robostix which is labeled G. When I checked
> > > with the multimeter the voltage seemed to be bouncing around all over
> > > the place between 0 and 3.3ish, so I moved my shared ground wire to 
>one
> > > of the grounds on the pwm ports. The voltage is now stable and the i2c
> > > is now working. I'm not too sure why it didn't work on the other 
>ground
> > > pin, unless pin2 isn't a ground at all?
>
>And just to double check - you got it working with the 20k resistors?
>If so, that's good to know.
>
>--
>Dave Hylands
>Vancouver, BC, Canada
>http://www.DaveHylands.com/
>
>
>_______________________________________________
>gumstix-users mailing list
>gumstix-users@...
>https://lists.sourceforge.net/lists/listinfo/gumstix-users

Hi Jesse,

> Have a side question about I2C with the Robostix.
> If i wanted to throw on another I2C analog to Digital Converter (not for
> robot sensor purposes but to check battery power and current so I could
> initiate a shutdown/hybernate mode for my robot, I was thinking an ADS7828)
> Could I get the Gumstix to read that off of the I2C header on the robostix?

Yep. The I2C header on the robostix is 5v, so you need to connect 5v
compatible logic to it.

> The reason I would want to use this is beause I'm going to be using most of
> the A/D on the robostix for actual robot sensors(Sharp IR's and some IMU's
> from Spark Fun).
>
> >From this diagram It seems possible to me but I'd thought I'd ask and look
> before I leap
> (I'm no EE guy so this kind of board diagram confuses me)
> Diagram: http://www.davehylands.com/gumstix-wiki/robostix-block.png
>
> And I'm just a bit confused about what was going on with the GPSStix with
> the other (20k) resistors but, are the pullup resistors already on the board
> or would I have to add them for the SCL and SDA if I used the Headers on the
> RoboStix?

The gumstix board itself runs at 3.3v and has no pullup resistors.
The robostix has a bidirectional 3.3v to 5v converter and has pullups
on each side of the converter (these are required for proper
functionality). The pullups are implemented using 10k resistors.

None of the other boards (excet roboaudio) have any pullup resistors
on the i2c bus.

The way i2c works, is by using open collector drivers. This means that
the device can pull the SCL or SDA lines low, but the pullups are
responsible for pulling the SDA and SCL high when a device is not
driving them low.

The reason for the 20k resistors to ground was to basically lower the
voltage that the SDA and SCL lines are being pulled upto.

With the 20k resistors added, it was forming a resistor divider
network with the existing 10k pullups on the robostix, to cause the
SDA and SCL lines to be pulled up to 3.3v rather thrn 5v.

3.3v is still considered by the robostix to be a logic high, and the
gumstix (through the gpsstix) doesn't want any more than 3.3v.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/