Modulated light receiver (CB21790E)

We found this circuit in a Mullard manual from 1960. The transistor is a phototransistor of the time. The gain is 3 dB.

Fast Sampling and Retention 2 (CB5957E)
This Sample & Hold circuit configuration is from an American 1980s documentation. The circuit uses...
Soil Irrigation Monitor (CB16439E)
By LED flashes you can get an idea of the degree of moisture in the soil. The sensors are wires...
Electronic Defense (CB22479E)
Found in an old Popular Electronics, the purpose of this circuit is to give a strong discharge in an...