We found this circuit generates signals from 200 Hz to 62 kHz and can be used to repel mosquitoes and mosquitoes. The circuit can be powered from 2 small batteries to 9 V battery.
The circuit below shows how to use an LM139 comparator or series equivalent as an amplifier. The...
We found this receiver circuit for modulated light in a 90s Popular Electronics. Equivalent audio...
The circuit was found in the February 1992 Radio Electronics magazine. The scale can be changed by...