The hunger of the microcontroller between two sleeps

by Denis Meyer | 12 December, 2018

If electronics, microcontrollers and measurement, notably of very low currents, interest you – which is logical because you are reading these lines – I’m sure you will waste no time in looking at this week’s episode of Elektor TV, having glanced at the title. It’s a comparative review of the µCurrent Gold from Dave Jones of EEVblog fame, and the Current Ranger from Felix Rusu of Low Power Lab, here used with an ESP32.

One of the primordial characteristics of the modern microcontroller is its nano-power consumption. It certainly needs current, but very little, and even less when it’s asleep. But when it wakes up its appetite will not go unnoticed. The circuit designer will no doubt want to monitor this sudden hunger, so it’ll need to be measured. But measuring current is, by definition, delicate, because it implies the insertion, in the circuit under test, of a measuring device. This foreign element inevitably presents a certain resistance, not always negligible.

A resistive foreign element

When the current to be measured is very low, the problem is no less tricky, in fact quite the opposite. When in addition the measured current contains spikes, the measurement problems become very thorny. In some cases, they will disrupt or even prevent the operation of the circuit under test. Actually, it’s not really surprising that a microcontroller would be disturbed by the introduction of a foreign element in its power line.

So that’s the backdrop for this week’s Elektor TV video. I am happy to have found one which succeeds in treating the work of active electronics techs in such a captivating and instructive fashion. Its news is more pertinent than ever as a result of the expansion of the Internet of Things. The IoT, which is in effect innumerable distributed modules, interconnected as often as not wirelessly. They pass endlessly from a catatonic state into one of frenzied communication, then go back to sleep. You can’t just measure their consumption with a multimeter, even in ammeter mode.

Good enough for the girls I go out with

Instead of this, some ingenious engineers have conceived for us some cheap measurement accessories. This video offers a comparative review: the µCurrent Gold from Dave Jones (EEVblog) and the Current Ranger from Felix Rusu (Low Power Lab) are here at the side of an ESP32 which sleeps and then wakes up. And using as an infallible reference a professional class equipment whose price puts it out of our reach.

The excellent video from Andreas Spiess starts off with a demonstration of exemplary simplicity and clarity. It ends with a summary no less perfect than the content. Between the two is a beautiful and instructive demonstration with a bit of humour as well, hidden in the details. “Grüezi YouTubers! “ (Grüezi: Swiss greeting.)