Instructables
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Picture of USB heated Mouse
I've never understood usb powered coasters that are supposed to keep your cuppa hot.
If your cuppa goes cold in the time it takes you to drink it, drink it faster. Coffee is medicinal, and you can never have enough tea.

However, with this inspiration, I can take a stab at another problem.
Why do fingers freeze when in contact with computer mice?
It seems I'm a bit late to this party, with commercial units for about $25, but it's so easy to do yourself with the seemingly endless supply of discarded mice.

With this in mind, I present my USB heated optical mouse.
 
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Step 1: Power

Picture of Power
So you want to make things hot.  Power is the most important thing.
If you place a hot cup of tea on a set of scales and allow it to cool, it looses about 25 watts of power by evaporation alone.
(measurable by mass of water evaporated per unit time * latent heat of vaporisation)
My soldering iron would have trouble keeping up with that.

USB specifications allow you to have 2.5 Watts total. (5V * 500mA) Feeble.  However, this can get comfortably warm.

To maximise power draw without your computer making a fuss, you can place 10 ohms accross the power rails in your USB device.
Two 22 Ohm resistors in parallel should do while leaving a bit of room for the original circuit.

In this case, I need a nice distributed heat so I'm going for two 10W wire-wound resistors simply for the size. Distributing the heat means you don't melt the plastic.

Szker made it!20 days ago

Thanks so much! I made this and am very inexperience with a soldering iron. My old Logitech MX518 just fits two of those big resistors.

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Chris_0606 made it!4 months ago

This is great, just made mine and its not hot but noticeably warm. I also had to butcher the plastics inside to squeeze them in, but it works and I am really pleased, thanks so much for taking the time to create the guide.

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Chris_06064 months ago

This is great, just made mine and its not hot but noticeably warm. I also had to butcher the plastics inside to squeeze them in, but it works and I am really pleased, thanks so much for taking the time to create the guide.

en_rov1 year ago

Just a correction, i think the mouse's power consumpion should be taken into consideration, since you are using all the 500 mA on the resistance, and typically a mouse uses around 100 mA (at least the ones I've seen). Just my 2 cents though, I thought it was worth sharing

sqm5 years ago
If you don't want to build it yourself, you could also buy one from http://www.comfortable-computing.com :-)
EGiR (author)  sqm5 years ago
haha the age-old time vs money dilemma. The parts were lying around. This mouse is currently plugged into the desktop so it's always on... It's winter here and the mouse is this constant body-temperature. We thought it would be a novel waste of time, but it's paying off!