This circuit, which is present in other points of this website, was found in a 90s Hands On Electronics. The circuit activates a buzzer with an oscillator.
This circuit was obtained from a 1977 magazine, but can still be mounted using BC548 for TR1 and...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
The figure shows how to add a Darlington stage to an operational amplifier in order to obtain a...