This circuit makes use of an operational amplifier from the 80's. The circuit can be implemented with modern transconductance operational and TTL logic working as a shield.
This version of the circuit is from 2000, using a source of negative voltage that allows to obtain...
This somewhat complex circuit was found in the May 1984 issue of Radio Electronics magazine. The...
This basic circuit is from an old documentation. The relay must be 50 mA maximum and must have a...