This circuit was found in a Popular Electronics from the 90's. The components used are common and instead of the buzzer we can use an LED or a relay.
This circuit was obtained from a Philips documentation from 1968. The transistors can be replaced...
The figure shows how to use the XR2206 to generate sinusoidal signals in a different way. The...
This headphone amplifier has good gain and high input impedance. The circuit is from Electronics Now and...