Found in an old English publication, this circuit applies to the 240 V network, but can be changed to lower voltages. Transistors are mostly general-purpose, admitting modern equivalents.
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...