>>potami+d01
There's a bunch of publicly available documentation about how the Canopus star tracker on the Voyager probes works out there, last I looked, and it's quite an interesting design by modern standards. It uses an image dissector tube, which is weird and long obsolete vacuum tube tech that can measure the light in an electronically-controlled section of an image, to scan a slice of the sky around the roll axis of the spacecraft looking for an area in the right intensity range (which is fairly easy for Canopus since it's generally the brightest thing in that part of the spacecraft's view so long as the roll axis is correctly aimed at the Sun), and there's a bunch of hardwired digital electronics to control it and use that to adjust the spacecraft orientation.