I am at the second revision with the PCB at the moment. I did some tests with a ceramic resonator vs a xtal and the resonator performs well within specs, even with huge temperature fluctuations (I put one in the freezer and did a couple laps and heated one with a heat gun to +-90°C and did a couple laps).

Therefore I removed the xtal and replaced it with a resonator which is much much smaller.

I went with a 10MHz resonator and generate the 5MHz from a timer output (prescaler at 2) giving me more clock cycles between each transmission "bit" and by using timer output the machine cycles are still in sync with the carrier wave.

Secondly I was comparing my output strength with a Mylaps Hybrid PT and I noticed that my output was about 3dB less. In the new PCB I gave in trace length for trace width and went with 2oz of copper instead of 1oz resulting in a much lower series resistance for my inductor spiral antenna which in turn gives me a much higher output.

The overall thickness at the moment with eliminating the xtal is about 3.6mm. (I went with a 1mm PCB not a 1.6mm)

I have not tested RC4 compatibility. I'm merely focussing at the moment on having a user friendly version which doesn't require a complex IDE or isp/jtag pods to load in a new number. I'm currently stuck at the bootloader which accepts new parameters to be programmed into eeprom over a 1 wire interface. If can store them directly in eeprom and read them from there but it still requires an AVR programmer to push them into eeprom.

I actually live about a 1hour drive from the MYlaps HQ but I don't think they would be of much help. I haven't thoroughly analyzed the transponder output of an RC4 PT so I can't give you any feedback on that.


Anyways. I had to put in a new order at work and there was some room left on the PCB panels so I filled them up with the new PCB so I have about 150pcs laying around. So let me know if you want a couple or if you are interested in the gerbers. I'll upload the new schematic later as well.

Cheers.