LED mod in wireless mouse

[cruiser78]

I'm wanting to put a blue LED into my Logitech Mouseman Wireless Optical and can only seem to find 5v LEDs and the max voltage going through the LEDs is around 1.7 or so... somewhere I read about adding a resistor or something into the circuit so that the 5v LED would work properly on a 3v system but I just can't seem to find that page again (It was on a page about customizing the micro RC cars and adding lights to them using a 3v button cell). If I can't find a blue LED that is bright enough I might try some other color... or infrared (it'd be unique but boring... I've heard that it works good cause the sensor picks up infrared signals best or something like that)

 

[Taurus]

infrared? that's not visible by the human eye, you know. and i really doubt it would help the mouse at all. :huh:

 

[cruiser78]

I know that infrared is invisible thus the reason for it being boring.. but unique because I'd have an optical mouse that looks like it doesn't have ne batteries in it but still works normally... but I'd like a blue LED in it cause that would look cooler but the blue ones take a 5v current and with 2 1.5v batteries in the mouse it'll only supply a max of 3v for obvious reasons and at the LED the max voltage I got when the LED was at it's brightest was about 1.5v and the blue LEDs I can get from my local radio shack aren't even close to bright enough at 1.5v.. at 3 they would work but it won't get that high at the LED thus I was wondering if I could add in a resistor or something to up the voltage going to the LED or something.

note: I've heard that the sensors for optical mice are supposed to be more sensitive to infrared light... but maybe that's not true.. I don't know

 

[Zedric]

Well infrared is closer to red in the light spectrum so that should have a better chance of working than a blue led. Oh, and a resistor won't help you run a 5V LED in a 1.7V system, it will make it worse. The LED may work on its own but with a dimmer light than at 5V.

 

[scriptasylum]

Originally posted by cruiser78
I'm wanting to put a blue LED into my Logitech Mouseman Wireless Optical and can only seem to find 5v LEDs and the max voltage going through the LEDs is around 1.7 or so... somewhere I read about adding a resistor or something into the circuit so that the 5v LED would work properly on a 3v system but I just can't seem to find that page again (It was on a page about customizing the micro RC cars and adding lights to them using a 3v button cell). If I can't find a blue LED that is bright enough I might try some other color... or infrared (it'd be unique but boring... I've heard that it works good cause the sensor picks up infrared signals best or something like that)

The voltage drop resistor needed for an LED is actually quite simple. An LED has 2 major parameters:

Vf = the forward voltage drop across the LED when forward biased (turned on). Any voltage above this value needs to be dropped across a resistor.

Imax = the max current the LED will handle before it starts to cause damage.

Given these values, you can compute the resistor needed by the following:

R=(Vcc-Vf)/Imax

Where "R" is the resistor value in ohms and "Vcc" is the supply voltage. For safety, I usually use a value slightly less than the Imax value in my calculations. The computed resistor value will most likely be a "non-standard" value. You'll have to find one that is close or use a couple resistors in parallel, but if you need to round the value, make sure you round the resistor value up. Rounding down will increase the current through the resistor.

Unfortunately, in a device as small as the mouse, you may have a bit of trouble locating the existing resistor to replace it with the new value. It may even be a surface mount device (really small and easy to overheat with a soldering iron).

You may have a tough time getting a blue LED to work in a cordless mouse that used 2xAA batteries. This makes the supply no more than 3v total and a blue LED needs at least 2.5v or more to run. The end resistor value would be very small indeed.

Incidentally, if you want to use LEDs in other projects (like case mods, etc) and want to use the 12v supply, you also have to take the power rating of the resistor into consideration otherwise it may get too hot since it has to drop so much voltage. This is calcuated by:

P=I^2*R

Where "P" is the power in watts, "I" is the current (which is the same as the Imax value), and "R" is the resitor value in ohms.

Ok, enough Electronics class. Have fun.

 

[cruiser78]

Thank you.
I took physics last year so I shoulda known that... but since I'm outta school now I kinda haven't been trying to remember a whole lot from then.

 

[scriptasylum]

It's been 10 years since I've been to school for this, but I like to tinker so it's easy to remember.

 

[Maveric169]

You know what you might try, convert the mouse to use a 9V battery and step down the voltage from there. You would have to replace the resistors to the led. And with that much "extra voltage" you could probley do a fan mod with it also. Or you would just have a mouse with a much longer battery life. If I had an extra wireless mouse I would play with arround with it. That would be a fun experiment. Anyone have a extra MS wireless mouse? Even if it doesn't work? If so let me know.

 

[scriptasylum]

Actually, a 9v battery wouldn't last half as long as 2 AA batteries. A 9v's voltage is simply higher, but it's amp-hour rating is reduced substantially. A 9v battery essentially is 6 1.5v cells in series, while a AA battery is one 1.5v "big" cell. Therefore the amp-hour rating is much greater. I think you would find yourself swapping batteries much more often that with the AA's. I suppose you could get a couple of rechargable 9v batteries and always keep one charged while the other is in use.

A normal 3v regulator circuit could easily be built for the mouse innards (using an LM317T regulator found at your local RadioShack), while feeding the LED with the full 9v; but there are losses associated with linear regulators. You could design some elborate switching regulator circuit instead, but that is beyond the abilities of most people, not to mention the space constaints in the mouse. The only advantage to using the 9v battery would be that it would be easier to get the blue LED to work.

Edit:

Oh, one more thing about the blue LED idea: let's not forget that the photosensor may have to be replaced too. The one currently in the mouse may have increased sensitivity to the red wavelength. Unsure about this though.

 

[cruiser78]

from what I've been reading from other blue LED mods in corded mice, the blue works just fine for the most part but on some mice it has some glitches on dark surfaces... and that's also why i've been thinking about going infrared. Infrared is closer in wavelength to red than blue is and I've heard that the sensors are optimised more towards the infrared wavelengths... I might try yellow out too.. that'd be a bit different.