The Chip That Has No ADC but Still Knows When Its Battery Is Low

Somewhere out in the field, a tiny battery-powered sensor is quietly dying. No warning light, no alert, nothing. One day it just stops responding, and nobody knows why until someone finally goes and checks it by hand.

How do you stop that from happening? The obvious answer is measure the battery voltage. But what if the chip you are using was never given an ADC(Analog to Digital Converter) to measure anything with?

No ADC means no voltage reading, right? Not quite. Nordic's nRF5x family, including the nRF51 and nRF52 series, has a sneaky little piece of analog hardware built right into the silicon that does not care about your missing ADC at all. It is called POFCON, the Power Failure Comparator, and it solves the whole problem with almost no power budget.

Here is the story of how it works, and why it beats a traditional voltage divider for this job.

The Familiar Way: ADC + Voltage Divider