Flysky TH9X ER9X FrSky Telemetry Conversion Without RS232 Level Converter

I've been saving this mod for my friends quad while waiting for his  new FrSky modul (FrSky DF 2.4Ghz Combo Pack for JR w/ Module & RX) as the stock modul has raised doubt of its reliability for us who fly at Ampang area. There has been a lot of reports from fliers using Flysky and Turnigy 9x having problems with the stock modul.

FrSky has made a reliable modul for this TX at an affordable price which come with a telemetry capabilty. You will need a telemetry ready RX from FrSky to make use of its function and a couple of sensors with its FrSky DHT-U Telemetry System to display all its telemetry information.

With Flsky/Turnigy 9X flashed with custom firmware such as ER9X, we can have all the telemetry data directly on our TX screen without the use of DHT-U. That's awesome. Now get your soldering iron heat up.

I am really thankful to those genius people out there who made this modification possible and thanks to them for sharing it. As a typical 'not so smart person' myself, figuring out all this modification by myself would be something impossible. It won't even came across my mind to figure it out myself.

With all been said, this modification didn't come from me. I just happen to search for the way to do it which suit the skills that i have. I've found this WIKI to be helpful but most of it involve building a cuircuit and then I found this to be the best way for me to do it -> FrSky telemetry mod without RS232 level converter.

WARNING: THIS MODIFICATION INVOLVES SOLDERING SMALL THINGY AND MAY CAUSE PERMANENT DAMAGE TO YOUR 9X BOARD.

All the infos need for this modification can be found on the link that shared above. But one important information seems to be left out and i only found it after going through the whole post.

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.

Modifying the modul

I don't have the SMD resistor as shown in the link above so i just used the one at hand. I have to warn you, the track that you need to work with here is too small. I almost backing out from doing this modification. So be sure you have the skills and tools to do it.

On The Board

The red wire is from the previous haptic feedback mod. 

Two resistors removed.

There's some modification to the board on pin two. For detail follow the link above.

Connector used for the ease of future work.

After all the modification done if you turn on your TX it will show both your THR and AIL switch is active. This is because your firmware still looking for both signal from the old pin on the processor. So you have to flash your 9X with the er9x-FrSky firmware to make it right and to have the FrSky menu option on your 9X.

For all detail explanation on the modification please go to the link above.

Sensors

As I am building this TX to be use with DJI Naza-M quadcopter this sensors seems to be useful to be incorporated with the system.

FrSky Battery Voltage Sensor - FrSky Telemetry System

FrSky FSH-01 Telemetry Sensor Hub (You going to need this for the sensors below to work)

FrSky FVAS-01 Telemetry Variometer Sensor

FrSky FAS-100 Telemetry Amperage Sensor

FrSky GPS-01 Telemetry GPS Module

For the time being, I am only using the voltage sensor for this build.

I've soldered the two positive an negative open wire to the quad distribution board where the wires for the battery connector are placed. This is to measure the pack voltage on flight.
I'm using the 2S setup on the sensor for a 3 cell by de-solder and soldered the positive wire on the signal side.

The rest is setting up the TX to read the data properly.

I leave the jumper which come with the RX on and plug the voltage sensor to A2. The jumper is for the RX voltage data.