This circuit was found in an American documentation from 1975. The components of the time can no longer be found easily, but they can be tested equivalent.
This amplifier can be powered with voltages between 2 and 5 V with power up to 100 mW. The minimum...
In the figure we have the way to control a TIC series triac with a reed switch. The current in the...
This practical idea from a 1992 documentation shows how to count the turns of a winder using a...