This circuit was found in a 90s Popular Electronics. With it, using a 4066, it is possible to control between 1 to 100 the gain of an operational amplifier like the 741.
This circuit is from a 1980s Motorola documentation. The circuit can be made with modern...
This well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...