This circuit is from a Hands-On Electronics from the 90s. The integrated amplifiers used are well known. The range is a few tens of meters depending on the resistance of the cables.
The basis of this circuit is a National Semiconductor operational amplifier that functions as a...
This circuit was found in an English magazine in 1983 but can be assembled with BC558. However, the...
This simple emergency charger (as it does not have many resources) consists of a rectifier and a...