This circuit uses a resonant reed relay to recognize the frequency of an input signal. Adaptations can be made to obtain functioning as a shield. The circuit is from 1965 documentation.
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...
This configuration, widely used in our articles and on this website, uses a 555 to control a relay...
This circuit was found in an English documentation from the 90s. It uses a PLL CMOS 4046 and is...