Darkith

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:

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.
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

tx3 tx3

TX prototype

hellcat

RX4 prototype on 12" hellcat

Stats:

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)

Notes:

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

Downloads

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.