We found this circuit in the July 1971 Radio Electronics magazine. The circuit activates a Sonalert or a relay for a higher power warning system.
The transmitter shown can reach around 100 meters depending on the location and sensitivity of the...
This circuit was obtained from a 1978 Practical Wireless. It generates a low frequency, low...
Using the LM170 integrated circuit, this circuit was found in the May 1970 Radio Electronics...