Pwm Fan controlling when arduino is dead?

Hello, First of all if I'm posting this in the wrong place please move it. I'm Trying to control a fan using Pwm to a arduino. However i ran into a problem when i powered down the arduino to simulate a failure and see what it would do The fan speed went to zero. Is there a way if the arduino fails for any reason that the fans can go to 100%? I'm searching online everything i found is for 2 pin fans. can someone help me to figure this out please?


hello I'm sorry i forgot to also say that I'm using the arduino zero board.


That is what I expected. Without power how is the fan to operate. When the PWM stopped it turned off the driver I think and the power source. Post a schematic of your design not a frizzy thing including all power and ground connections. You can reconfigure your output to fail ON and the fan will go to full speed but no Schematic now way to know how to do it.

Hello I'm not good at drawing. I will try my best to get something shortly.


How to make a schematic you can post.

There are different failure modes.

Disconnection of the power results in the Arduino's output pins going high impedance, but if the ground of the Arduino is still connected to the ground of the fan the clamping diodes will prevent you from pulling up the voltage on that pin. If not connected any more, the fan input is floating and its reaction may be different. In any case, the outcome is probably predictable.

Another failure mode is a software crash. As the PWM is created in hardware this may continue - but never change duty cycle. Or the pin remains in its last state - output, maybe high, maybe low. The latter is unpredictable.

Maybe there is instead a random hardware failure. Now behaviour is even less predictable.

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