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 with an industrial standard 4-20 mA interface uses a KPZ20G pressure sensor but can...
This simple receiver with germanium transistor and listening on a crystal phone was discovered in a...
This circuit is from Motorola technical documentation from the 70s, but it can be easily assembled...