WebUSB / Headphone connection to Espruino

You should be able to use normal digital pins and pinMode(pin,"input_pullup") - then you can use setWatch. Rather than trying to use the RS232 serial protocol, you could actually just send a series of pulses - a long pulse for 1 and a short for 0... That way you don't have to worry about the polarity of the input signal.

If you did want to use software serial there's some code for it here though: https://github.com/espruino/Espruino/iss­ues/549#issuecomment-175083164