Suggested by a 90s EDN, this circuit supports almost any LED as a source and a phototransistor as a detector. The circuit operates with a PLL 567 at a frequency of around 40 kHz.
This circuit can be used for several purposes such as pulse counter, pass counter, roulette, etc....
This circuit is from Radio Electronics. The magazine no more exists, but the circuit can be...
We found this circuit in a French documentation from the 80's. The components used are still...