How to modify your 9x to support telemetry
The following guides have been created by different members of the community to explain how they approached the mods.
A good suggestion would be to read all of them! Then decide which method you would like to follow. As a general rule they all follow much the same formular, just with different hardware configurations.
* FRSKY Telemetry details by Phil http://er9x.googlecode.com/svn/trunk/doc/FrSky%20Telemetry%20%20details.pdf * FRSKY interfacing tutorial by gruvin http://code.google.com/p/gruvin9x/wiki/FrskyInterfacing * FRSKY Telemetry mods by Mike Blandford. http://er9x.googlecode.com/svn/trunk/doc/TelemetryMods.pdf * FRSKY telemetry guide by Rob Thomson http://www.rcgroups.com/forums/attachment.php?attachmentid=4157979 * FRSKY conversion without the level converter http://www.rcgroups.com/forums/showthread.php?t=1510047
To run the FRSKY build of er9x you will need to make some modifications to the hardware in your radio. These modifications require soldering of small tracks on the radio circuit board, as well as solder two little wires on two of the CPU pins. This modification will re-route two of the switches (THR and AIL) and allow the Atmega 64 to receive telemetry data on the pins where these switches were formerly connected. Be warned that it is possible to damage the board permanently if care is not taken.
Shown in the picture is a overview of the modification.
Note: If this is done on a module that uses the pins of the module bay (DJT) and you want to use the two unsused pins on the module to carry the telemetry data, the two matching pins on the th9x's back board MUST be isolated on the top and bottom side of the board, or the module could break. Also not shown in this picture is the 2K7 resistor that would be used with the DJT module to allow updating of the module without damaging the 9X. (please check Mike Blandford's telemetry guide. Link below)
Using FrsKy Upgrade Lite as Level Converter
Well now it's better that you have a look at this tutorial By Mike Blandford on how to do the telemetry mod so we can have on screen telemetry on the 9x tx. http://er9x.googlecode.com/svn/trunk/doc/TelemetryMods.pdf
In his tutorial Mike uses another level converter with a MAX232 chip. We will only replace it with the FrSky Upgrade Lite. All the rest is the same. Please read it carefully.
I would ask you to pay special attention to the part where he explains how you should cut the traces on the back PCB of the 9x in order to isolate those 2 pins and use them to route the TX and RX lines to the FrSky Lite. You fail to do this the right way and you will probably damage your module. This applies if you're using the FrSky DJT module. If you are using the DHT module you won't need to cut those traces as you're not using those pins.. Here is a picture from the back board of my other radio. It's only the side that faces the back of the radio. Note that you will have to cut traces on the other side as well. Always check with a multimeter to confirm that the pins are completely isolated form the traces. Sorry, this is the only picture I have
Also note the 2 resistors on Mike's mod.. The first one, 2K7 (2,7 Kilo Ohms) that connects to the module's RXD line and goes to the FrSky Lite TX pin. And the second one, 470 Ohms that goes from the Frsky Lite to MOSI (pin 2 of the Atmega 64) on the 9x main board.
Since the frsky module talks rs232 and the atmega 64 talks TTL you need to use a level converter to connect both.
frsky upgrade lite
What is the FrSky Upgrade Lite? It's basically a level converter and it was designed to mainly upgrade the firmware of the old FrSky D8R receivers. It should be connected between the computer serial port (RS232) and the receiver itself. To upgrade the FrSky modules it's not necessary to use it because they already talk RS232 and can be directly connected to the computer's serial port or to the FrSky USB adapter.
Here is a modified copy of Mike's schematic explaining how to connect the FrSky Upgrade Lite.
VCC and Ground
Here is a picture of where to connect VCC and ground on the back board
DHT DIY module
If you are using the DHT DIY module, you don't need to put the 2K7 resistor on this one because if you need to upgrade the module you will have to disconnect the plug anyway, so there is no connection between the main board and the module. Therefore this resistor is not needed.
Here is a picture
Do this mod at your own risk and also all that rubbish that people normally write on disclaimers ;-) It worked for me and others. Please check and double check all the connections and only apply power when you're really sure that all is correct. I don't have to say that you must always remove the battery before working on your radio, or there is a chance of releasing that magic smoke that is trapped inside ;-) Good Luck and Happy flights..
thanks to joao for making this guide. The original guide is available at http://9xforums.com/forum/download/file.php?id=1431