This analog frequency meter for low frequencies was found in Radio Electronics magazine from July 1958. The circuit has several scales with the frequencies indicated in the diagram.
This circuit is from a Radio Electronics from October 1963. The LDR and transistors are from the...
The figure shows how to use an operational circuit as a voltage divider. The circuit is from a...
This is the basic configuration of an operational amplifier as a current regulator. We found it in...