Noise coming from my mouse (sort of) need some advise

Thread Starter

NTkiller

Joined Aug 6, 2013
18
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).
So your saying use a large capacitor (like I said), but put a resistor in between the usb 5v rail and the caps/rest of the mouse. I tried a large capacitor, and it helped, but not as much as I would like. I bought a 100 microhenry choke, and it made little effect (the guy at radio shack said to use it). I think someone posted on here to use one rated for 5.6 milihenries, so when I get the chance I'm going to return this choke and ask the guy at radio shack to order the right one. I've noticed that the caps will affect the low frequencies more than the high frequencies, while the inductors will do the exact opposite. The noise my mouse generates is quite high in frequency (I know they are over 8 khz because my mom cannot hear the noise, and I know her hearing cuts out at 8 khz), Thus my reasoning would suggest an inductor would be more suitable in this situation. I'll report back when I get the part.
 

DickCappels

Joined Aug 21, 2008
10,153
NTkiller,
Nobody can tell you the part number for the inductor you want because nobody knows how much inductance you need and how much room you have for the inductor.

Using one winding of that transformer was a successful experiment. Now its a matter of trying other inductors to see how well they work. A good way to start is to look for the highest inductance with a resistance of 5 ohms or less that you can find that still fits in the available space. You are probably not going to want to put it inside the mouse because that would affect the way the mouse feels.

The 5 ohm number was based on dropping 200 millivolts at 50 milliamps. Higher resistances might also work.
 

THE_RB

Joined Feb 11, 2008
5,438
As the mouse PSU voltage is not critical you can just use a resistor and not bother with an inductor. That was what I was trying to say in post #20.

Because the LED is pulsed with a very short duty cycle a resistor and large cap should be enough to decouple the very fast LED current pulses from the USB 5v supply rail. Obviously an inductor could be better but is probably not needed. :)
 

MrChips

Joined Oct 2, 2009
30,707
The noise my mouse generates is quite high in frequency (I know they are over 8 khz because my mom cannot hear the noise, and I know her hearing cuts out at 8 khz).
That is a rather unusual analysis and conclusion.

I doubt if your mom can hear an LED flashing at 8kHz or lower frequency.

Maybe she can hear your mouse squealing if you swung it by its tail.
 

ronv

Joined Nov 12, 2008
3,770
The link to the inductor I posted is available at Mouser.com. It was the biggest one I could find quickly with fairly low resistance that I thought might fit.
 
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