This circuit was found in an article in Electronics Now magazine from March 1997. The transistors are general purpose, and the indicator is a 1 mA full scale analog type.
This simple half-wave control using an SCR, which may be TIC106, has been obtained from a US...
I found this circuit in an English publication from 1989. This configuration can be mounted with...
This reader with TTL logic compatible output uses an LM139 comparator. The circuit was found in...