Found in a 90s Elektor, this circuit is based on a Maxim integrated circuit of the time. The circuit supplies 5 V at its output with a maximum current of 50 mA.
In this circuit of a 1991 publication, we can use the 2N2646 unijunction transistor and the sensor...
An interesting circuit suggested to indicate when a device is turned off. In the figure we have...
This amplifier was found in a 1969 Mullard documentation. The circuit uses transistors that have as...