I am attempting to control the fan speed with a Mosfit. All works well accept for a buzz from the fan anything less then 1000 (see code). I think I need a filter of some type but do not know enough info to design such. Thank you for your help, Rick . eisman7@gmail.com
I have some suggestions for you.
- Never post your email address on any public forum.
- Never post your sketch as a screen shot. No-one will want to re-type it into their system. Post it as text between code tags. See forum guide.
- On Uno, analogWrite() can take values between 0 (=0% speed) and 255 (=100% speed). 900 is equivalent to 132 (=51% speed) and 1000 is equivalent to 232 (=90% speed).
- Connect a fly-back diode to the fan terminals to prevent damage to the rest of the circuit and your Uno. 1N4001 or similar will be fine. A 0.1uF ceramic cap to reduce electrical noise is also a good idea.
- There is a lower limit of the PWM below which a fan will not start. This limit will be different for each fan.
- There will be a lower limit of the PWM below which a fan will not run. This is lower than the limit at which it will start. So to run a fan at lower speeds, you must give it a short "boost" to make sure it starts.
Hi,
What are the specs of your fan?
If it is a BLDC fan, then it will not like running on a low duty cycle current supply.
The BLDC has electronic circuitry inside to drive the motor, it assumes it is getting DC.
When you get to low duty cycles, it like firing short pulses at a circuit that is designed to use DC.
If you want a speed controlled computer fan or any BLDC fan, you need a four wire unit.
The four wires are, positive supply , negative supply, tacho pulse output and PWM speed control input.
Tom.... 
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