I am obsessed with all things LEDs and lasers if you haven’t already noticed. One device that I have always been absolutely fascinated with is a laser projector. These devices take laser sources and reflect them off 2 mirrors (one for x and one for y) to cause the laser beam to be steered. When this is done at high frequency, persistence of vision causes patterns to be seen. These devices are normally used at concerts and the like.
The devices that are used for this beam steering are called mirror galvanometers and can oscillate back and forth at up to 100kHz with very precise movements over a couple degrees deflection. I decided I wanted to try and make one of these devices and design all the analog control circuitry too.
The galvos (short for galvanometers) use differential capacitive rotational position sensing for the feedback and audio amplifiers for driving the coils of the galvo. Two coils are wound and connected in series as the actuation method, rotating a magnet attached to the shaft.
Unfortunately the design suffered from control loop instabilities and the event I wanted to build it for came and went so, sadly, it now sits in a project box to be resurrected at some point in the future. I didn’t however totally give up on the idea and ended up buying various parts from AliExpress to make one.
Fred Temperton 