Written in an article in Radio Electronics magazine in April 1987, this circuit triggers an alarm via a relay. Details of the sensor are given in the article.
With changes, this circuit from a documentation of the 70s, can be adapted to use more modern...
Found in a 1968 EEE, this switch controls a high-power load from an audio signal. The current is...
In this circuit the gain decreases as the input signal intensity increases. The circuit is from a...