Hello, I've had an annoying problem with my optical USB mouse ever since I got it years ago. When you connect the mouse to the front USB port and a pair of headsets to the front audio jack of the PC, you can hear a buzzing noise in the headsets. This noise is consistent to the behavior of the mouse's led. The noise's pitch lowers as you take the mouse away from the table, and increases as you lower it back to the pad. The noise also goes up an octave when you move the mouse. I know it's this mouse since it has happened with different computers, and it's not my computer since a similar mouse in the same configuration does not make this noise. I would really like to keep this mouse since it is very smooth and works like a dream. IIRC, this noise is coming from the mouse switching the led on and off at a high rate of speed. I've been fiddling around with the mouse's internals, and I found out when you bridge power and ground with a capacitor, the noise gets a lot quieter. but, the first time you hook up the capacitor to the mouse, it knocks out the mouse, and the mouse appears to reset. I think this is the mouse losing power to the inrush current of the capacitor. I know USB has an inrush current limit, so I came here to ask about a simple circuit I could build and place inside the mouse to get rid of the noise the mouse puts out on it's power lines. It needs to have an inrush current under the limits of the USB standard (whatever that is), and keep the noise from getting back to the PC. Any ideas.

 

Dear friend,I dont know if you solved your problem.It seems unsolved.The noise you hear comes from the produced operational frequency of the leds.There is a possibility of missing good ground from your earphones.

 

I found out when you bridge power and ground with a capacitor, the noise gets a lot quieter. but, the first time you hook up the capacitor to the mouse, it knocks out the mouse, and the mouse appears to reset.

What is the value of the capacitor that you tried?

Details, details, details.

 

If you just solder the cap in it probably won't trip the mouse because the voltage will come up slow. You could also try one of these:
http://www.fair-rite.com/cgibin/cat...t&THEPART=Round+Cable+Snap-Its#select:onepart , but it might be a pain hanging on the cable.

 

To Athineos, I don't think this is a ground fault in my pc because this noise has occured with a different computer. To MrChips, the capacitor I used was 16v, 470 uF. I don't think a capacitor is appropriate here since the noise got a little quieter, but not enough. Also, I hooked the capacitor up to the mouse while it was plugged in to the PC, and the mouse light went out and came back on. I think this was the inrush current of the capacitor causing the mouse to lose power. If I were to use a capacitor, it would have to be a large one, and I would need something to limit the inrush current. To ronv, I tried winding the cable up in a choke, but that did not help. I noticed that the link you gave pointed me to chokes that dealt with frequencies in the MHz range, but my noise is audible, which means it is below 20 KHz. Do they make chokes that work in the audible range of frequencies? Or would a combination of choke and capacitor be more appropriate?

 

If I were to use a capacitor, it would have to be a large one.

Your logic is flawed. A capacitance of 470μF is way too big.
Start off with 0.1μF ceramic across the power supply and see what happens.
Next, add 10μF/16V electrolytic in parallel with the 0.1μF.

Don't go higher than 10μF. If that does not help you will have to find another solution.

 

I thought that a bigger capacitor would be better at cancelling out my noise, but I'm no expert. I'll try a smaller one. Thanks for the tip.

 

I tried what you said. The ceramic capacitor had no effect, while the 10uf cap had a tiny effect. any suggestions?

 

These tend to make noise when you plug them into a USB and try to click them. Capacitors don't help. Saran Wrap seems to work after a few minutes.

 

Maybe NTKiller is resting his elbow on the Mouse's tail .....

Ramesh

 

Personally I'd just replace the mouse. A £1 optical USB mouse from the local pound-shop works fine for me.

 

These tend to make noise when you plug them into a USB and try to click them. Capacitors don't help. Saran Wrap seems to work after a few minutes.

hahaha, very funny, but that doesnt help me. And I would like to keep the mouse.

 

You might want to try placing an inductor between the mouse and the capacitor. That should improve the attenuation of ripple current propagating "upstream" back toward the computer chassis.

Since the problematic signal appears to be at audio frequencies, the inductor will probably have to be many millihenries. I suspect Mr. Chips has a better idea of a good value to use.

See the illustration at the link below.

http://tinypic.com/r/33ubgwj/5

About the 470 uf stopping the mouse from working: You might want to try disconnecting your mouse and turning off the computer, then soldering your 470 uf capacitor in place, then plugging the mouse in and turning on the power? If the risetime of the power supply is slow enough, then everything should work.

 

Thanks, I'll try that when I get a chance.

 

OK, I found a way to get rid of the noise. I took a transformer from a HVAC unit I had laying around and I hooked the low voltage side inline with the mouse's power, and the noise was gone. you could still hear a tiny ripple, but nothing like it was. This transformer is WAY too big to fit within the mouse, so I need something that has the same inductance as this transformer. I don't know if this will help but the transformer is a 240v to 24v transformer rated for 40 volt amps. Thanks for the tip, BTW.

 

OK, I found a way to get rid of the noise. I took a transformer from a HVAC unit I had laying around and I hooked the low voltage side inline with the mouse's power, and the noise was gone. you could still hear a tiny ripple, but nothing like it was. This transformer is WAY too big to fit within the mouse, so I need something that has the same inductance as this transformer. I don't know if this will help but the transformer is a 240v to 24v transformer rated for 40 volt amps. Thanks for the tip, BTW.

Enough for the job,eh?

 

So can someone give me a part number for a inductor that would do what I need?

 

You have an open(or high resistance equivalent) in your mouse cable shield, or somewhere in the soldering at the mouse end or at the molded plug on the other end.

Case closed

 

Maybe 5.6 mh in this would fit? I'm guessing the mouse doesn't draw more tha 30 ma or so. Put a 10 Ufd on each side of it like in post 13.

http://www.fastrongroup.com/image-show/37/07M.pdf?type=Complete-DataSheet&productType=series

 

40-50mA average when the LED is on (when the mouse is moved).

I would try a large cap inside the mouse across +5v and GND. Like a 470uF electro, and a 0.1uF cap in parallel with it.

Then I would decouple the incoming USB +5v rail with a resistor. you can afford to drop about 0.3v and since the mouse uses about 50mA tops a resistor of R = E/I;
R = 0.3/0.050
R = 6
(so use a 5.6 ohm 1/4 watt resistor).