BBB GPIO 1.2 v on GPIO pin when set to LOW

I have been playing with the GPIO pins both through the OS as well as Python using the adafruit libraries, and I am seeing some strange behavior. When I connect an LED + 470 Ohm resistor to GND and a GPIO pin set as OUTPUT, I see the LED glow dimly (i.e there is a slight voltage present) even when the pin is set to LOW! When I set the pin to HIGH, however, I see the expected result (i.e the LED lights up normally).

This behavior is seen with all GPIOs, and I am wondering if it is normal. Shouldn’t the voltage across the GPIO pins and GND be zero when set to low?

I have an Element 14 RevC. with the latest Debian installed.

Any help/insight would be much appreciated.

If you connect a voltmeter what do you see ?


I get about 1.2v when the BBB is powered on. This voltage is present on all GPIO pins!

As mentioned earlier when the pin is set to OUTPUT and LOW I get 1.2v. However, when I set it to HIGH I get 3.3v. Subsequently, after setting it to HIGH, when I set it back to LOW the voltage drops to zero!

1,2V is called a “float”. On power up all GPIO pins are set to inputs.