Arduino voltage on 5V and 3.3V pins have doubled

Im working on a project with some servo motors, a hc-05 bluetooth module and an arduino nano. for some reason the arduino has started outputting around double the voltage on the 3.3V (6.7V measured) and 5V (9.5V measured) pin. this has damaged the bluetooth module. Other than the output voltage the arduino seems to work fine.

I think it must have been caused by faulty wiring on my part, but i have not found the problem yet, and it has been working with this setup for a while.

Does anyone know what the problem could be, and of its fixable, and is it safe to use these output pins if it is not fixable?


How are you measuring those voltages? What are you using to measure those voltages? What is the power supply to the Nano? How is the supply connected to the Nano?

Post a schematic. Show on the schematic the points of measurement.

measured with a multimeter. the power supply is 12V (4x AA) on the Vin and GND (also used for the servos)
schematic (only pins 0 and 1 have been used for hc 05 rx/tx and 7 more servos)

the measurements have been made between the GND and the 3.3V/5V pins

I really do not see how the Mega328 chip can still be working with 9.5V on the 5V (Vcc) line. The absolute max voltage to Vcc is 5.5V by specification.

In the photo, is the Nano powered by USB?

The Nano is covering the range setting on the DMM. Can you move the Nano?

ah im an idiot, the multimeter was on the wrong setting. now it shows the expected voltage on the right setting. still wondering if something is worng with my setup since my hc-05 seems to have died.

thanks for the help

The HC05 input pins are not 5V tolerant. There should be a level shifter on the HC05 RX pin from the Nano TX pin to drop the Nano 5V to 3.3V. A resistor voltage divider is often recommended. It is possible that you have bricked the HC05 by applying 5V to the RX pin.

See this page.

4xAA equals 4x1.5V equals 6V :wink: Back to school :smiley:

It appears the HC-05 is powered directly from the 6V battery.