PIC12F675 + RC5 + PWM + fan (noise problem)

FJMSoft · Joined: 20 Oct 2013 Posts: 36

Hello.
I'm trying to make a very small and simple fan controlled by IR (RC5).
Will be 3 fans, very small ones (200mA).
Receiver is a TSOP1838 "compatible" (MYS1838) connected to external interrupt.
I already made a working code, received the RC5 and controlled fans speeds using a timer PWM, no problem in code.
Test code just reads the RC5 and sets fixed PWM values.

Problem is (as somewhat expected) when fans are powered the IR sensor gives several output as an IR received, but really was not an IR received, I believe it is noise!

How can I workaround this?

Thank you very much.

temtronic · Posted: Sat Jan 11, 2014 3:31 pm

some ideas:
If you have access to an oscilloscope, you should be able to see where the noise is coming from. I suspect that the power supply is 'drooping' when those fans are powered. 3 x 200ma= 600ma, so I'd use a 5 amp rated supply.You also should have 18ga wire to the fans, bypass caps(.1/50v).as well as bypass caps near the PIC. If the PIC is powered from the 'fan' supply, I'd decouple it with a PI filter of 3x 10uf caps and 2x 10r. Layout is important, good grounds are essential. You might need some filtering on the IR detector output so check the mfr's website or datasheet. You might need to filter the power supply to that device as well.

hth
jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19545

It is worth remembering that a motor in a fan will draw much higher 'pulse' currents, than it's rating. If the fans are 'brushless' designs (common now), they will have pulse currents well above the average 'rating'.

Have a look at:
<http://www.digikey.com/classic/documentredirector.aspx?doc=https://www.digikey.com/Web%20Export/Supplier%20Content/ComairRotron_25/PDF/Comair_Tutorial_BrushlessDCFans.pdf>

(for somewhat larger types, but the principles are the same).

Remember also that the starting current can easily be 5* the rated current....

Also with any load containing inductive components, there will be flyback to deal with when the load is switched off, and if these are brushless designs, this will be happening hundreds of times per second as they run.

Best Wishes