Optocouplers/Optoisolators
There are times when we want to completely insulate two circuits, but still pass signals between them. We can do that with a relay. However, a relay is very slow. It takes around 10–30 milliseconds to switch on or off. We can't do PWM or communications at this pace. However, there is a clever Integrated Circuit (IC), called either the optocoupler or the optoisolator, which does exactly that.
In this recipe, we will use an optocoupler to switch on an LED with a completely different circuit that has its own independent power supply.
Getting ready
Following are the ingredients needed for this recipe:
An Arduino board connected to a computer via USB
Two general 220-ohm to 1,000-ohm resistors
A breadboard
A 1.5–3.0 V battery, preferably with wire terminals
A general LED
A general optocoupler/optoisolator such as the TLP621, 4N35, or LTV-816
How to do it…
Following are the general steps to connect an optocoupler to the Arduino and then to connect another circuit containing an LED...
