![Image](http://www.pyrofersprojects.com/images/padtxsmall.jpg)
I used an RF module from a 9x transmitter (fs-tm002) and an AVR to generate the ppm signal to feed it.
I have a small LiPo that I fit inside the TX module and have a dc2dc step up going inside the pad.
The 4 shoulder buttons are wired to aux channels, each channel sits at MID until you press the button, that puts it to high.
Its got 500mah in the LiPo, the DC2DC has 500ma max, so it should get a minimum of 1 hour of use per charge.
I've not flown with it yet, still waiting for the stepup, but tested it with a arduino running the multiwii code and all the channels/buttons work as expected.