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, ...

This simple temperature relay circuit can be used to signal a fire or setpoint for temperature monitoring function. You need to adjust P1 so that T1’s base voltage is 0.5V smaller than the emitter ...