Modifying your FrSky Q X7 to work with Team Blacksheep Crossfire Micro TX
If you’re subscribed to my YouTube channel (You’re not? Do it now!) then you’ve probably heard – the FrSky Q X7 transmitter has some issues with the new Team Blacksheep Crossfire Micro TX module.I’ve talked about it a bit here:
Basically the rundown is that at some point FrSky changed something in the hardware on the Q X7. We know that early models lacked the s-port on the bottom, and those models work fine with the Crossfire. The recent models that have the s-port however do not work. This has to do with the fact that the hardware cannot support the 400k baud rate at which the Crossfire was designed to function when using the CRSF protocol.
Now here’s the thing – the X7 was never designed to support more than 100k baud, since that is what the s-port uses. When Team Blacksheep designed the original Crossfire they tested with the Taranis and discovered it could support 400k, so they ran with it. When developing the Micro TX they tested with the X7 and low and behold it supported it too… but they were testing with one of the old units. So FrSky changed up the hardware and broke the 400k baud capability. Malicious? Probably not, in spite of what many people online may think. This is just what happens when you design a third party product out of manufacturer spec. It may work for a while, but there’s no guarantee that it will work with later hardware revisions. This is normal, no use playing the blame game.
Team Blacksheep and the OpenTX team are working on a fix, which most likely will come in the form of a software update that will slow the baud rate down to 200k. This shouldn’t be an issue with the amount of data traversing the link right now, but may limit the hardware in the future (at least as far as the X7 is concerned). There is no ETA yet on the update, but it should be soon as both parties have confirmed they are communicating with each other and are close to release.
If you are really brave, skilled, and impatient, you can opt instead to modify your X7. It isn’t easy as you’ll be removing tiny SMDs and soldering wires to tiny, spindly legs, but it does work and allows the full 400k baud.
In the video above I mention two modifications, but later data revealed that only one of them actually worked. This mod involves removing a tiny transistor from the PCB inside the X7 and wiring in a similarly tiny inverter. The whole thing is outlined in the original GitHub thread by user “nathanielakkermans”, and I am including his text and images below for posterity.
Again, I don’t recommend doing this unless you are 100% sure of your abilities, or you have a spare radio to use in case things go south.
on the backside of the main PCB i removed the transistor Q400
then i soldered the output of the inverter in one of the pads of the Q400.
the input for the inverter i soldered on the s-port pin(this one is parallel on the s-port pin of the module). and i get the 3,3 volt from one of the capacitors nearby.
as mentioned before, i used the 74LVC1G04 inverter for my mod, i checked the datasheet and the input can take up to 6,5 volt before failing.
after this mod i tested the internal transmitter module and it is working perfectly fine, solid link ald also telemetry data and the betaflight LUA script is working normally.
i believe there is no downside on this mod, i know the PPM level can be vbat level, but s-port is only used on the more advanced modules with bidirectional communication like the crossfire.
the crossfire and the internal module are using 3,3 volt level signals on the s-port and i’m guessing most of the modern advanced modules use these levels, but i don’t know this for sure.
i hope this can help someone of you out there how had the same problem
The above text as posted by GitHub user “nathanielakkermans”, as well as all the other details of this issue, can be found in the original GitHub issue.
For what it is worth I can verify that the above mod, when done correctly, does work just fine.