DigitalPin Output Voltage doesnt rise Problem

Hello everyone,

I use an Arduino Uno for a self-regulating, heated box. The temperature inside of this box shall be within a selected temperature zone. For switching the heating element I use a MOSFET with this schematic:

External Power Supply with 12VDC
Resistor to GND: 1K (I had no other resistors with higher resistance)
Resistor from Arduino to Gate: 680 Ohms

When I set the output PIN to HIGH, the
voltage rises just to 0.1V, the current is then just < 1mA
(so obviously not a short) going from the controller to the
MOSFET. When I disconnect the MOSFET, the digital PIN comes
up to 5V right away, powering a LED without problems. So the
microcontroller with its digital PIN is okay. But:

Powering the MOSFET directly with +5V from the arduino, also
works absolutely normal. The current from the 5V source to
GND is then about 5mA (because of the 1K-Resistor to GND).
With the manually set +5V I'm completely able to turn on the heating elements, the MOSFET not even get warm. So absolutely normal behavior.

Do you guys know what could be the problem here? Its oubviously located on the pcb with the Mosfet, but why does the arduino not power the output pin with more current to reach a higher voltage?

Just the combination of working digital PIN and
working MOSFET does not work...

Regards, Tim

We are going to have to make guesses because you did not post your code (HINT)

My guess is that you have not set the pinMode() for the output pin to OUTPUT

Maaan! You're a legend. How could I oversee that?!? I already worked on that project for many weeks, wrote more than 1000 lines code, and these pinMODE basics at the very beginning. Thanks a lot, you saved me from soldering the MOSFET's completely new...

I did not recognize this, because LED's put to these PINs with 1k- resistors were working normally. So now it works normal... Thank for this hint. Sometimes it's easier than you'd think :slight_smile:

If the problem is solved then we don't need to see it but I hope that you got the hint about posting your code