N Mosfet pulldown resistor Voltage drop

Other Hardware General Electronics
1

Hi,
I hope you all can help me getting my night sleep back because I have an issue with a mosfet (IRLB8721). What I want is driving a motor with 9V where an Arduino Nano V3 IoT has logic turning the motor on and off. Idea is that I send a 3.3V signal (pin 10) to the gate of the mosfet to turn the motor on and set the pin to low to turn it off again. Both the motor and Arduino have their own powersource (motor 9V and Arduino is now connected to a laptop via usb). What I read everywhere is that I should use a pull down resistor between gate and ground/source but I can't get this working because the voltage between the gate and source of the Mosfet drops to 0.64V when I add a 10K resistor which is too low to set the mosfet in ON state.

See my schema below. What am I doing wrong here?

mosfet-issue
mosfet-issue1998×1275 290 KB

2

My "random guess" is that it's not a 10K resistor. Maybe 10 Ohms? Maybe some other "low" value.

Do you have a multimeter to check the resistance? (Take it out of the circuit to measure it.)

3

Share your code so we can see how D10 is handled.

1 Like
4

Hi DVDdoug,
Thanks for your reply. I don't have such a fancy multimeter. But the package says 10K ohm with brown black orange gold bands.

5

Thanks for rubberducking Mancera1979. While copy and pasting the code I found out I commented out setting the pin 10 as output. After I fixed that it worked. Thanks again.
Was convinced the error was in the circuit but it was the code in the end :slight_smile:

1 Like
6

That´s not the way to drive the MOSFET. You can damage Arduino. You need a resistor to limit the output current from pin in Arduino.