This guide will take you through the steps I took to get telemetry data from my XJT module displayed on my Turnigy 9X. This will work for most of the rebrands of TH9X radio, including the FlySky 9X. This will not work for the 9XR Pro or any of the “i” models of Turnigy radios e.g. the TGY-i6S.
Before starting this mod, note that I have already successfully installed the module and used it on models without telemetry and I have already flashed the ER9X-FrSky firmware on the radio. Both of those mods need to be completed in order for this telemetry mod to work, but I will not go over how to do them here.
- Soldering Iron (with a tiny tip)
- Tweezers or Needle Nose Pliers
- Glue Gun
- Philips Screwdriver
- Razor or Dremel for cutting the PCB
- Multimeter to test isolation
- 2x 220 ohm resistors
- 1x 1000 ohm resistor
- 1x 10k ohm resistor
- Breadboard (prototyping board)
- 2N3904 Transistor
- Single core wires (an old computer IDE ribbon cable is perfect)
- Any connector with 2 wires (to disconnect the mod if need be)
This is the most complicated mod you are likely to do to this radio, so carry it out at your own risk! There are plenty of opportunities to destroy your radio during the modification, so if you would rather spend some cash to get a radio with the features already built-in, have a look at the FrSky X7. I accept no responsibility for any mistakes you make or any aspects of this guide that may cause damage to your radio.
Step 1: Rerouting your Throttle Cut and Aileron Dual-Rate switches
Remove the battery and XJT module from your radio and unscrew the screws on the back. Gentle pull the front and back of the radio apart to reveal the circuitry inside. Note that there is a colourful wire loom connecting the front circuit boards to the rear circuit boards. You can unplug that loom until the modification is complete.
Towards to bottom of the main circuit board (in the front shell) is the ATmega64 processor. Just below the processor are two rows of SMD (surface mounted) resistors. We are going to remove the first two resistors on the top row (starting from the left) to free up the processor’s first two pins, which are used for RXD and TXD.
Take your hot soldering iron and pliers (or tweezers) and heat up the first resistor until you feel it move with your tweezers. This should only take a few seconds and signifies that the solder on both ends of the resistor has melted. Lift the resistor off of the board and put it to one side. Due to applying heat to the whole resistor, it is likely that it is now burnt out. We wont need that for this mod, so you can throw it away.
Repeat the process for the second resistor until both have been removed.
Just below both resistor locations are small vias (metal rings with a hole in the middle). We are going to use those vias to reroute the switches to processor pins 41 and 42 using wires and our 220 ohm resistors.
Optional: If you look closely at those vias, you may notice that they are covered in the green solder mask that covers most of the circuit board. If this is the case for your board, take a razor blade and gently scratch away some of the green around the via to expose the metal. A lot of the guides on the internet do not mention this, so I can only assume certain boards do not have this problem.
We now want to connect the first via (the one on the left) to processor pin 41. The top row of pins on the processor run from 48 on the left to 33 on the right. You will need to solder a wire to bridge the via and pin and then insert one of the 220 ohm resistors somewhere along that wire. Personally, I soldered one end the resistor to the via and then soldered a wire to the other end of the resistor and pin 41. Ensure that the metal of your wire and resistor does not touch any other part of the circuit board or components, as this will cause a short and may damage your board. I held my resistor in place with tweezers and smothered it in hot glue before doing any soldering.
We now want to repeat this process with the second via and another wire and 220 ohm resistor. You may find it helpful to add solder to your wire and iron’s tip just before trying to solder the wire onto the processor pin. You only want to make contact between the processor pin and your iron for a matter of seconds, otherwise you may burn out the processor. Also, avoid tugging at the wire after you have soldered it to the pin, as the pins are very easy to pull away from the board and that would be disastrous.
Ensure that your wires and resistors are secured to the board with hot glue (or whatever method you choose) as they may vibrate when you carry the radio. This first step is complete.
Step 2: Connect your XJT to the TH9X
We are now going to isolate two of the pins that slot into the module. Please note that I have a resistor and wire coming from Pin 2. They are not required for this modification. Nothing needs to connect to pin 2.
Take your Dremel or razor and cut a gauge in the board to break the connection between the pin and rest of the circuitry. Simply put; you need to cut through the green solder mask, through the copper underneath and into the grey fibre of the board itself. Use a multimeter to check whether the pin is isolated by holding one end of the meter on the pin and the other on the solder pads at the bottom of the board. You will notice before isolating that there is a voltage detected on one of those pads (to signify it is connected to the pin). When you have made all the cuts to isolate the pin, that voltage will no longer be detected.
We now need to isolate pin 5, which is the bottom pin and used for the S.Port data. This isn’t as difficult on the green side, as it only needs to be done on the right (see image), but you will need to scratch away at both sides of the pin on the black painted side, just like with pin 2. Again, keep testing this with a multimeter until you do not get a voltage anywhere on the board.
We now need to solder a wire from pin 5 to the middle leg of our transistor on the inverter circuit board..
Step 3: Inverting the Signal
Before you connect the wire from pin 5 to the main board, we need to introduce a signal inverter. The XJT uses a signal that the processor cannot interpret unless it is first inverted. This involves making a small circuit board of our own. The easiest way for you to do that is to copy the diagram below.
I hot glued my inverter onto the main board.
Step 4: Setting up the radio
Assuming you have put your radio back together and plugged the module and battery back in, we now need to go through the menus and set up the firmware. At this point, it is worth mentioning that you should have flashed the ER9X-FrSky version of the ER9X firmware. The standard version does not have the telemetry options and will give you switch errors when powering on.
Before you turn the radio on, hold the left trim switch to the left (the one just below the throttle for Mode 2 users) and switch the radio on. This will show a slightly different splash screen and upon it’s release, will show a hidden Hardware option in the Radio Setup menu.
I’ve made a quick two minute video on carrying out this mod. It certainly isn’t as detailed as this guide, but if you’re an experienced modder, you might find it sufficient!
Thank you to everybody who has posted guides for this modification online. The guides I found particularly helpful are listed below. I would also like to thank MikeB from OpenRC forums, for answering a couple of my questions about the mod.