Testing for failure with a multimeter is only partially effective, whereas a dedicated optocoupler testing circuit provides clear results in just seconds. For related tutorials and step-by-step build ...

Have you ever needed to power a 12-volt relay in a circuit but only had 6 or 9 volts available? This simple circuit will solve that problem. It allows 12-volt relays to be operated from 6 or 9 volts, ...