[SI-LIST] Re: Audio And Fan Circuits interference
- From: Steve Rogers <SRogers@xxxxxxxxxxxxx>
- To: "'bart.bouma@xxxxxxxxx'" <bart.bouma@xxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Fri, 14 Feb 2003 11:33:48 -0000
Lots of good input here, lets generalise then home in.....
We have 3 Basic ways you are going to get your inteference from the motor
bits on your audio:-
1. Conducted
2. Electric field coupling
3. Magnetic field coupling
Usually, the conducted path is found to be the problem but this is also the
most simple to address. A nice and quick way to see what the best level of
conducted inteference you can achieve is to run your audio circuits from
batteries. This way you know the only way the inteference can be getting to
your audio circuits is by options 2 or 3. (Note for completeness we should
also include RF coupling but I doubt this is applicable for your system)
Once you are running your audio from batteries if its all nice and quiet
then all you need to do is clean up the power supply. As already pointed out
this is a simple case of filtering but you do need to ensure you do it
right. A point to note is that where currents are small your filters can use
resistors as opposed to inductors. We could spend all day discussing
filters, ill leave it to you.
If you still have noisy audio running from batteries then you need to think
a bit more about whats going on. With motors your probably talking about
magnetic field coupling somewhere. Get a magnet field probe (inductor on the
end of a bit of coax) and connect to a spectrum analyser to find where the
guilty circuit bits are then look into how to sort it (put distance between
tbe source and victim, shield things, change orientations etc)
One other thing worth looking into is where you are routing power supply
lines and also where the ground returns are. You often see designs with EMI
problems which are due to large currents in supply lines/ground return paths
coupling to signal traces carrying small signals.
This lot is by no means exhaustive but should get you started....
Fill your boots
-----Original Message-----
From: Bart Bouma [mailto:bart.bouma@xxxxxxxxx]
Sent: 14 February 2003 08:05
To: brahim@xxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx;
jonpowell@xxxxxxxxxxxx
Subject: [SI-LIST] Re: Audio And Fan Circuits interference
Hi,
Does the motor have brushes? If so the motor can produce a lot of EMI.
Filtering this motor or taking a brushless one would solve your problem, I
think.
Another cause can be the controller circuit. Is it a PWM-controller?
Bart
"Jon Powell"
<jonpowell@xxxxxxxxxxxx> To: <brahim@xxxxxxxxxxxx>
<si-list@xxxxxxxxxxxxx>
13-02-03 17:45 cc:
Sent by: Subject: [SI-LIST] Re:
Audio And Fan Circuits interference
si-list-bounce@xxxxxxxxxxxxx Category:
Please respond to jonpowell
Does the fan circuit share VCC and GND with your audio?
That is a common source of noise.
jon
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Brahim Koudssi
Sent: Thursday, February 13, 2003 6:53 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Audio And Fan Circuits interference
Hello,
I have designed a board that consists of an audio circuit and a fan
controller circuit.
When the fan is running it induces audible noise in the audio circuit, I
can hear in the speakers the fan spinning.
Can anyone please address the following questions:
1. How's the fan audible noise getting into the audio?
2. How can I get rid of this interference?
Thanks,
Brahim
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