#tictaccode_Teensy.ino

#A timestamp generator for cameras with USB mic input (not SMPTE LTC)

This Teensy 4.0 code produces a BFSK modulated audio signal via Direct Digital Synthesis (DDS) and outputs the signal through the Teensy USB audio device. The payload is the UTC time obtained from a GPS attached to Serial1.

Writing of the word is triggered by a hardware interrupt provided by the GPS one pulse per second (aka PPS). Before the BFSK word starts, a spike is produced to precisely mark the start of the UTC second. This spike is used by the python desktop postproduction program, tictacsync (doing a crude and naive FSK demodulation).

Details about audio-video syncing with those hardware dongles can be found at the project home.