User Tools

Site Tools


Information under voltage warning on raspberry pi

The B+ has an under voltage detect trigger which results in the power led going off when voltage drops below about 4.65V. The signal is also available on a gpio line (GPIO35).

Latest firmware update will display a warning symbol in top right of display when this is detected. It will also disable turbo mode while the warning is displayed to try to reduce the chances of crashing.

I've also added a warning symbol to the existing over-temperature condition (> 85'C), which also disabled turbo mode.

Currently the symbols are: Red square: over-temperature Rainbow square: under-voltage

As usual you can override the behaviour in config.txt if you understand the risks: avoid_warnings=1 removes the warning overlay. avoid_warnings=2 additionally allows turbo when low-voltage is present.

For testing you can make the temperature warning trigger more easily with “temp_limit=50”. You can probably trigger the under-voltage check by using an insufficient power supply (perhaps USB socket from PC), or a dodgy micro-usb cable from ebay.

Run rpi-update and report back if it behaves as expected. You will need a B+ to test the under-voltage state. The over-temperature should work on any Pi.

Under voltage

Throttling arm due to temperature (80-85'C)

Throttling arm and gpu due to temperature (85+'C)

Source :

- created date : 2017.02.21 -

voltage_symbol_of_raspberry_pi.txt · Last modified: 2017/02/21 14:53 (external edit)