This series and parallel sensor circuit was found in Popular Electronics from the 1990s. Any SCR can be used and the supply voltage depends on the load.
This circuit uses two TTL trigger inverters to generate signals that can be adjusted at R1. The...
Suggested by Siliconix in 1980s documentation, this circuit uses currently uncommon components. The...
Suggested by General Electric in 1966 documentation, this circuit uses unusual components today....