File	Date	Author	Commit
circuit	2011-03-23	Torsten Dreyer	[9dd380] Some documentation
firmware	2011-03-25	Torsten Dreyer	[3eef81] fix wrong tts calculation
panel	2011-03-23	Torsten Dreyer	[9dd380] Some documentation
README	2011-03-25	Torsten Dreyer	[d4b1b9] Reduce precision of KTS and introduce in-range ...

Read Me

This is the DME indicator for the radio stack of 
the FlightGear PMPT. All sourcecode files are licensed under the
GPLv2 or later, the schematic and all other artwork is
licensed und the creativecommons attribution share-alike CC BY-SA 3.0.
You can find the licenses here:
http://www.gnu.org/licenses/gpl-3.0.txt
http://creativecommons.org/licenses/by-sa/3.0/

You may reach the author at       Torsten(at)t3r(dot)de
Try to convert this into a valid e-mail address. Please don't expect 
an immediate response - I don't work on this on a full time base.
You may write in German and English.


The DME is based on Atmel's ATMega8 microcontroller and feeds
new life into an old real-life dme indicator of an unknown
manufacturer.
Connection to the FlightGear simulator is done by a 
two-wire-interface, the i2c bus, interfaced to the computer 
using the i2c-tiny interface found here:
http://www.harbaum.org/till/i2c_tiny_usb/index.shtml

The DME supports the following features:
- display of FLT (flight time, time since powerup)
- display of ET (enroute time, resettable timer from ET-button)
- display of distance to station (sent from FlightGear)
- display of speed (sent from FlightGear)
- display of TTS (time-to-station, computed internally)
- working TEST-button (displays test-patter)
- dimmable 4+1/2 digit 7-segment LED display by panel control
- software dimmable panel lighting (white LED driven) (from FlightGear)
- software power on/off (from FlightGear)

The I2C address is hardcoded to 15 but changeable in twi.c. 

The I2C/smbus registers are
Address 0: distance to station as a two-byte word, represented as 
           tenth of a nautical mile. Write 543 for 54.3NM
           Initial value is 0 (zero). 

Address 2: speed in tenth of a knot as a two-byte word. Write
           1453 for 145.3KTS. Inital valuel is 0 (zero).

Address 4: brightness of the panel illumination as a single-byte
           unsigned integer. Legal values are 0 for off and 255 (0xff)
           for brightest. Initial value is 0xff.

Address 5: Position of source-switch as a single byte unsigned integer
           Values are 1 for NAV1, 2 for NAV2 and 0 (zero) for HLD.

Address 6: power as a single byte unsigned integer. Write 0 (zero) for 
           power off and any other value for power on. Initial value 
           is 1 (power on)

Address 7: in-range flag as a single byte unsigned integer. Write 0 (zero)
           if the dme station is out-of-range or 1 if the signal is valid.
           DIST, KTS and TTS displays a decimal point only if the signal is
           invalid. Initial value is '1' (valid)