This circuit is from a 1975 RCA tube manual. It appears elsewhere on the site. R5 depends on the voltage of the amplifier with which it is used and can be changed.
This simple injector circuit can actually be powered by voltages from 3 to 9 V. The frequency is...
This simple timer can be used in many applications such as egg timer. The LED glows up when S1 is...
This circuit locks after a short touch on the sensor. The circuit can be powered by voltages from 5...