This current meter with many scales was found in a 80s American documentation. The operational amplifier is from that time, uncommon nowadays.
This configuration from a 1976 technical documentation shows how to use a varicap in a direct...
This circuit was found in the October 1979 issue of Radio Electronics magazine. The circuit is...
When this alarm is off current drained is very low, only about 60 µA. The circuit can be powered...