In the figure we have a simple way to produce tone in a piezoelectric transducer. The frequency depends on the capacitors and the supply can be done with voltages from 1.5 to 6 V.
This circuit uses a TL071 to differential amplify the signals from a microphone and thus reduce...
We found this circuit in a 1995 publication. It makes use of infrared LEDs of the type existing at...
This circuit is from September 1984 Radio Electronics. The frequency can be changed by changing C1 and...