Squeezing A PPM Line from an FS-TH9x

Unless you’re an RC nerd, this post will be extremely boring.  You have been warned.

I wouldn’t say it was a complete waste of time but I certainly could have been doing any number of more important things last night.  That’s what I get for being a cheapskate and buying discount copies of much nicer transceivers.

Just looking at it makes me feel dirty now.
Just looking at it makes me feel dirty now.

So they advertise these as a 9 channel PPM/PCM/PWM capable TX and RX combo but there’s a couple of technicalities in that.  The RX doesn’t actually output PPM or PCM.  Sure there’s a version B that does and they just did their best not to tell you that this isn’t the one you’re buying.  Now there’s that 9 channel problem as well.  The RX only outputs 8 channels.  It only takes a little research to work out a schematic and firmware for a viable DIY version if you really need PPM from an RX module.  Of course after drawing that up, I realised I was short a PIC or so and it was already 1am.

What else aren't you telling me?
What else aren’t you telling me?

For my immediate needs, I gotta have every channel I can get, it has to be PPM output, but I couldn’t give a rats arse if it’s wireless.  I just needed to test a flight control units higher functions.  Amongst those bent truths FlySky  has been telling me is a little ray of light.  It turns out that the TX unit actually uses PPM to communicate with the RX before the RX converts it to a useless output.  The thing I’m getting at here is that you could hijack the PPM signal on its way out and route it to somewhere useful.  So let’s get this ridiculous butchery under way.


A feature of these transceivers that’s often overlooked is the trainer assist configuration.  Basically someone, who’s a better pilot than you, can link their controller to yours while you’re still learning to fly and save you from crashing your shiny new aircraft in the event push something silly.  The little cable they use to link controllers just so happens to speak PPM.  So grab a 3.5mm stereo jack or cut up some headphones.

Screen Shot 2016-08-14 at 1.41.46 pm

Now if you tie those 2 rings together (as indicated by the black ground leads you can see above) and then to the earth pin of a 3-Pin servo connector cable you’re half way there.  Tie the tip (indicated by the red lead) to the signal pin of the same servo connector and you’re done.  Unplug the transmitter module from your TX then plug your new cable into the back of the TX unit.  Throw your TX into student mode and you’re outputting PPM.  But we can squeeze more out of this.  Time to void that TX warranty, so open that controller up!


Here’s a nice little page that details the steps to flash the er9x firmware onto your FS-TH9x.  I’m not going to detail it, but I will warn you to install the old version 0022 of Arduino IDE or you’re gonna have a bad time.  Once er9x is installed, you can just jump into the settings for your controller and get creative with the channel mixing.  Dropping it into PPMSIM is a nifty trick that let’s you out all 16 channels (yup 16 channels) via that groovy PPM cable we made earlier.  Pair that up with an arduino and you can even use it to control flight sims on your PC.


Thanks to Richard Prinz for the tip on that one.  His web site there should help you through the rest of that.

Now for me this is the end of the road.  I got my PPM, tested the flight controller, was horribly disappointed that the feature I was hoping for doesn’t work on it and have had bugger all sleep in the process.  Next time I’ll spend the money and get the full spec brand name controllers.

0 comments on “Squeezing A PPM Line from an FS-TH9xAdd yours →

Leave a Reply

Your email address will not be published. Required fields are marked *