LIBRARYDigital isolation.

Sometimes two parts of a system have to trade digital signals without sharing a ground wire, for safety or to stop a noise loop. A digital isolator does exactly that: it carries the bits across an insulating barrier, so the two sides pass data with no direct electrical connection between them.

Why isolate at all

There are two reasons. Safety: keep a person, or a delicate circuit, on one side clear of any fault current on the other, which matters whenever mains power or a human body is in the loop. Noise: when two grounds sit at slightly different voltages, current flows in the ground itself, a ground loop, and isolation breaks that loop by cutting the shared connection.

How it crosses the barrier

An isolator has a transmitter on one side, a receiver on the other, and an insulating barrier between them that blocks direct current while letting the signal across. The barrier is often a tiny capacitor or transformer built into the chip; an older optocoupler uses light across a gap. What never crosses is a direct electrical or ground connection.

Isolating a whole bus

To isolate a bus like SPI or UART, you pass each of its signals through its own isolator channel, matching the direction of each line. A four-wire SPI link needs four channels routed the right way. The controller then talks to the peripheral exactly as before, with the barrier invisible in the middle.

A One Thousand Drones isolated bridge board does this on purpose: a full SPI bus crosses a digital isolator so the sensor side and the computer side never share a ground, which is what keeps a person safe when the sensor sits on skin.