#tictaccode.ino

#a Timestamp generator

This code produces a BFSK modulated audio signal via Direct Digital Synthesis on the SAMD21 DAC output. Timing of DAC samples are done with TC5. The payload is the UTC time obtained from the GPS attached to Serial1. Writing of the word is triggered by a hardware interrupt: the GPS one pulse per second (aka PPS) cabled to Adaruit QT Py pin '15/A1' . Before the BFSK word starts, a small blip is output on the DAC to precisely mark the start of the UTC second. This blip is a full scale ramp attained in 10 samples and is used by the python desktop postproduction tictacsync program (doing a crude and naive FSK demodulation).

Each SAMD21 boards have different blinking light (Dotstart, NeoPixel, plain LED...) so choose the sketch according to your board (beware that tictaccode_QTPY.ino needs a patched Adafruit_NeoPixel_ZeroDMA.h for driving the onboard NeoPixel with DMA (see this thread).

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