Found in a1967 Ferranti documentation, this circuit uses an operational amplifier from that time. The circuit uses a LDR as a sensor and has a null setting.
The circuit shown is from the National Semiconductor Linear Applications Handbook of 1994. using...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30...