This simple circuit to monitor the frequency of the power grid uses an analog indicator. The adjustment trimpot can be 4k7 and the indicator is 100 mA full scale.
This circuit is from a Popular Electronics from the 90s. Its gain is 22 dB and can be used as a...
This simple source is suitable for audio amplifiers providing an output voltage of 32 V with a...
This circuit is from the 80's but uses common components today. The relay is voltage sensitive...