There are many Iambic keyer implementations on Arduino, but not many with Raspberry Pico. This is a (incomplete) port of Steven Elliot's (K1EL) keyer (which first appeared in openqrp.org website).
Iambic Mode B is not implemented yet (mainly because I don't use it). Patches welcome.
The toughest part for me was maintaining the timing with time_us_64(). Where we capture the free running timer matters. I haven't measured the resulting waveforms, but I think the output mostly matches the input WPM that is asked.
For now, changing WPM/Sidetone frequency/pins would need editing
main.cpp and recompiling the code.
Output sidetone goes into the PWM output. A low value resistor and an electrolytic capacitor in series is recommended before connecting the negative pin of the capacitor to the speaker. i.e.:
GPIO pin |- ...\/\/\/\/.....)|---- 🎧
The original code was licenses GPLv2.1 or above. Since we derive from that code, this code too has the same license. Please share your improvements and fixes.