This circuit uses an unusual sensor nowadays, but the configuration can be adapted to more modern types, as well as the operational amplifier. The circuit is from an 80's documentation.
Suggested for use in cars and motorcycles, this circuit was found in a 90s Popular Electronics. The...
This is a typical 3 ½ digit TTL counter. We found it in the September 1973 issue of Radio...
This receiver, whose tuning range depends on L1 and L2, was found in the 1992 special edition of...