This circuit solved a problem encountered in developing a portable device with an ARM Cortex-M0 processor. The power supply consisted of two AA batteries (2 × 1.5 V), and I needed to signal the user about the battery's state. The Cortex-M0 operates from 3.3 V down to 2.0 V, and an AA battery is considered discharged when its voltage drops to 1.1 V, so the available supply is 1.1 V × 2 = 2.2 V. This was a very low-power application that could work down to 2.2 V, so it was not necessary to warn the user to change the batteries until that voltage level was reached...
Register or Sign in below to download the full article in .PDF format, including high-resolution graphics and schematics when applicable.