Monitor battery voltage

Hi Tobias,

Well, one very simple method is to detect when the battery voltage goes below ~3v. Basically as the battery voltage lowers, the voltage regulator stops being able to supply 3.3v to the STM32 chip in Espruino - and you can detect that.

You can use E.getAnalogVRef() to see what voltage Espruino thinks it is at, so for instance you could do:

setInterval(function() {
  if (E.getAnalogVRef()<3.0) doSomething();
}, 60000); // every 60 sec

To go to sleep, you'll want to have called setDeepSleep(true) - but then you should probably do that anyway if running off a battery as it'll decrease power draw massively. Then, it's just a matter of making sure you don't have any calls to setInterval or setTimeout that might wake Espruino up.