The code for the “Personal Lap Timer” (PLT) is now working.

The PLT reads the first valid transponder ID it sees after power-up, stores it to EEPROM, then calculates lap times for that transponder while ignoring all others. The results are sent via RS232 to an external computer.

The RS232 signal is currently logic-level, which doesn’t conform to the true specification (that requires voltages below -3V), but the PC I’m using has no problem reading the logic levels.

While I have saved the transponder ID to EEPROM, and recall the ID and send it via RS232 to make sure it got where it was supposed to go, I’m currently not using the value stored in the EEPROM for anything else. I intend on including a pushbutton to tell the microprocessor when to acquire the transponder ID so there will be no need to re-acquire it every time the decoder is powered-up (which is now a minor inconvenience).

The next (vitally important) step will be to test the system with transponders in moving cars, and modify things depending on the effects of interference from the motor, ESC, radio, etc.

I’ll post the last schematic, showing connections to the microprocessor, shortly.