Metronome using operational (CB22060E)

We found this circuit in an English publication. The transistor can be BC549, and the power supply can be between 5 and 9 V.

Telephone Bell (CB25683E)
This additional bell circuit was found in the February 1994 Electronics Now magazine. The...
Delayed Reed Relay (CB12185E)
A delay of a few seconds to a few tens of seconds can be achieved with this circuit found in a...
Single Transistor Alarm Circuit (CB24372E)
This circuit uses a transistor to trigger the alarm from a low quiescent current sensor. The relay...