This circuit is from the 80's but uses common components today. The relay is voltage sensitive according to the power supply used. Transistors may be general purpose types.
In the figure we have the way to obtain a voltage indicator for a 3-terminal voltage regulator. The...
September 2017 - SparkFun offers through Mouser Electronics its protboard solderless board that...
This input stage has unit gain but a high input impedance and low output impedance. The circuit is...