Arduino Forum

Using Arduino => General Electronics => Topic started by: roli on Jan 26, 2011, 03:30 pm

Title: Sensor interferance and USB
Post by: roli on Jan 26, 2011, 03:30 pm
So back in the old forum I posted a question right before the upgrade to the new forum. Since I haven't solved my problem yet I am reposting this topic.

Link to the old forum:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1295719923/
Title: Re: Sensor interferance and USB
Post by: MikMo on Jan 26, 2011, 09:55 pm
I would try the same setup, but with another PC.
Title: Re: Sensor interferance and USB
Post by: Grumpy_Mike on Jan 26, 2011, 11:13 pm
From your other post
Quote
As for common mode choke - what could that be?


A common mode choke is two coils wound together on a single core but in opposite directions, any large transient signal on both lines will be suppressed as each line generates a magnetic field in opposite directions and they cancel out.
Quote

What I don't get is this - sensors themself are digital. They output 1 (if IR light is detected) or 0. So the only way that the interrupt gets triggered is if somehow the voltage on the arduino pin drops (the interrupt is configured to trigger on falling voltage) when I turn on the light.

No :- the sensor is normally a high impedance and can pick up transitory signals like a radio antenna does as well as the signal it is supposed to pick up. Try putting a 0.1uF capacitor from the arduino input to ground, that will help suppress pickup of interference signals.
Title: Re: Sensor interferance and USB
Post by: roli on Jan 26, 2011, 11:16 pm
I don't think pluging it into another computer would work. I just noticed that my wacom USB tablet blinks when I turn the light on. So proabably it has something to do with voltage drop.

Idea with capacitor looks like it might work. Of course this will be a little messy to do since the PCB has been made. But I will try it.
Title: Re: Sensor interferance and USB
Post by: MarkT on Jan 27, 2011, 03:28 am

From your other post
Quote
As for common mode choke - what could that be?


A common mode choke is two coils wound together on a single core but in opposite directions, any large transient signal on both lines will be suppressed as each line generates a magnetic field in opposite directions and they cancel out.



Really?
Title: Re: Sensor interferance and USB
Post by: Grumpy_Mike on Jan 27, 2011, 10:09 am
http://www.butlerwinding.com/store.asp?pid=28349 (http://www.butlerwinding.com/store.asp?pid=28349)
Yes
Title: Re: Sensor interferance and USB
Post by: MarkT on Jan 27, 2011, 04:47 pm
Look again, common mode chokes are parallel winding, differential-mode are anti-parallel.  If your unwanted signal produces no flux in the magnetic circuit, how can there be any inductance to choke it?
Title: Re: Sensor interferance and USB
Post by: roli on Jan 28, 2011, 04:55 pm
Quote
Try putting a 0.1uF capacitor from the arduino input to ground, that will help suppress pickup of interference signals.

I did this a few minutes ago and for now it seems to be working. It may just be luck since this problem sometimes doesn't appear but I think that it is working.