This 1967 modeling circuit mimics the whistle of a locomotive. The steam-shrieking wheezing is set in a 2k2 potentiometer.
We found this circuit in an English magazine from 1976. The magazine no longer exists, but just...
The phototransistor of this alarm can be of any type. The relay must be sensitive type according...
This circuit generates signals from 93 to 170 Hz in three ranges. The circuit is from an American...