I recently got this ancient Visomat light barrier made in eastern Germany (GDR/DDR) consisting of a transmitter and a receiver. By comparison to modern light barriers, this is indeed a visible light barrier, the transmitter contains a 6V/15W tungsten bulb. So I figured to build a controller for it and get it back to work.
Transmitter and Receiver
The receiver contains a phototransistor, due to the optics on the receiver there is still a fairly decently fine line of sight, not the full entry lens needs to get covered to register a trigger only the center most part. I wanted to keep the 6V bulb for one of my microscopes which uses this type however since I wanted to run everything off 12V anyhow I put a warm-white LED into it. On the receiver (which I haven’t made a photo off, but is just a 5k resistor and a phototransistor inside) I just attached a new cable.
Controller
The controller consists of an unregulated 12V power supply, a LM311 comparator which has a high-current (50mA) open collector output which I use to switch a signal relay. Some hysteresis circuitry is also present.
Front- and backplates of the enclosure are 3D printed to perfectly fit the SUB-D connectors. I used this OpenSCAD SUB-D stencil library to get the holes going.
In Action
