This circuit with the PLL4046 was found in the October 1994 Electronics Now magazine. The transistor is low power, and the volume obtained is small.
This circuit reinforces signals in a frequency range between 1500 and 2000 Hz for use in...
When a small air current reaches the piezoelectric sensor, a small audio signal is generated and...
This circuit is from a Poptronics, American magazine from August 2000. The circuit can be...