Micro siren (CB21234E)

This circuit with the LM3909 can be powered with voltages from 3 to 5 V. We found it in a Popular Electronics from the 90s.

Pre-Emphasis on 1500 Hz (CB13685E)
This circuit reinforces signals in a frequency range between 1500 and 2000 Hz for use in...
Wind Detector (CB5155E)
When a small air current reaches the piezoelectric sensor, a small audio signal is generated and...
Signal Injector (CB10325E)
This circuit is from a Poptronics, American magazine from August 2000. The circuit can be...