To make my previous log somehow more accessible, I draw this block diagram:

The whole string instrument is a string (pun intended) of four blocks -

VCO - voltage controlled oscillator. This is the circuit that generates sawtooth tone proportional to its input voltage. The length of string of resistive wire over fingerboard can be measured by its resistance, transformed into voltage and fed into VCO.

VCA - voltage controlled amplifier. As name suggests, its transfer to output is related to input voltage. I can use it to "mute string" (shut down oscillator output) when no string is played.

VCF - voltage controlled filter. In this case, low-pass filter. This one can be used to change tone color, depending on how much of force is applied to the bow pickup sensors.

Finally, amplifier adjusts amplitude of the signals from VCO, VCA and VCF to fit loudspeaker, so the output from instrument can be heard.

Except of VCO all blocks are designed to use analog designers classic inventory - opamps, OTAs, and comparators. For the VCO, I cheated and used microcontroller and two stereo DACs. The instruments is somehow modular, so I can exchange it for proper analog VCO if I wanted to.

In following project logs, I'll describe the basic blocks in more detail.