© <in der past>

DIY-UHF system

*BETA* This is a pretty basic beta version...with limited instructions included...consider yourself warned.

This system, in conjunction with an existing RC transmitter with four or more channels, forms a complete micro UHF radio system. There are two parts:

  1. The TX module taps into the PPM signal from the RC transmitter, and decodes the first four channels. The four channels are converted into a digital signal with a parity check bit, and then transmitted over a 900mhz frequency.
  2. The RX module receives the digitally encoded channels, and uses the values to drive 2-3 actuators plus a motor ESC.

Complexity wise, it's somewhat more difficult than the DIY-IR systems, but not too much of a progression.

Prototype pics


RX3 prototype


TX prototype


RX4 prototype on 12" hellcat


  • Currently hard-coded to 1 channel (915.00 Mhz), +90khz freq dev
  • 9600 bps data rate
  • 7-bit channel width (128 values) + 1 parity bit [dead-banding at center and extremes reduces this at RX side]
  • 4 channels parsed on TX
  • 3-4 channels produced on RX (AET, AETR)
  • Single cell Lipo power (should be good for up to 5v)
  • Throttle cut around 3/3.1 V on RX4 code (not tested)
  • Prototype 4 ch RX weigh in around 0.85 g. Using a TSSOP for the PIC will probably further reduce weight.
  • PFM performed on actuators (this code really sucks...hope to improve/replace it soon)


  • Tested on Hitec Flash 5 (so far)
  • Tested with Logic low PPM signal (logic high setting possible, not tested yet)
  • Tested with Hitec/Futaba channel ordering (JR & Sanwa settings possible, not tested yet)
  • Range tested to a basketball court (so far)
  • The TSSOP TX & RX chips are the hardest to solder, start there, and check for shorts between pins before proceeding
  • Low battery LED on RX3 not tested.
  • Pin assignments on PIC change from RX3 to RX4...don't mix up the PCBs and PIC code
  • Make sure you bridge the jumper points on the RX board after programming the PIC, there's four (Vcc, GP0,GP1, MCLR). I just use a little solder so I can ICSP the PIC with updated code.
  • My RF skills are limited, so I haven't really optimized it for range/signal rejection...feel free to contribute
  • No schematic per-se, I was more concerned with routing on the RX and too lazy to copy my paper sketches.
  • The PCB routing sucks...I know. But it works.
  • There's some surplus code that I haven't found time to cleanup, including some interrupt code that isn't used


Big thanks to Zlatko & RCGroups DIY-Electronics members

I can be reached at darkith /at/ gmail /dot/ com, or as darkith on RCgroups.

Commerical/for-profit use forbidden without permission.