Figure 1a shows a latching circuit based on an optocoupler, IC 1. If the off switch remains closed, pressing the on switch powers the LED in the optocoupler. Thus, the transistor in IC 1 turns on. You ...

Few realize how close an optical coupler resembles a relay. It is so close, in fact, that one can be wired as a Run-Stop latch circuit. One advantage over the relay is that it may be turned off via a ...