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Apple wireless keyboard converted to USB

rberthoud

Feb 22, 2016
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Feb 22, 2016
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Hi, folks... if anyone would be so kind to help a clueless dude who doesn't know the first thing about electronics..

I've just converted my working Apple magic keyboard, which runs (or used to run) on 2 AA batteries into a USB-powered keyboard... basically, I've connected the power wires from a USB cord into a sort of stick that is the same length as the two batteries put together and I stuck this homemade device into the keyboard in the place where the batteries would be... before you judge, I did it because the keyboard has been draining the batteries like sand drains water and I am really broke, so I can't keep replacing the batteries at this rate or buy me a rechargeable battery kit, as the good ones are out of my budget... so I worked with what I had...

The adapted keyboard works just fine (and as you can see I'm even using the keyboard to type this) and I ended up doing a reasonably neat job with the welding and such things...

But, as you might have already guessed, the problem is that a USB cord will feed my keyboard a 5-volt current, and the keyboard was originally designed for 3 volts (since it requires two AA batteries in series), right?
So I am concerned that the tension difference might damage my keyboard in the long run (I imagine they must design the circuits to sustain the little disparities that may occur in the daily usage of the device with no damage, but I honestly have no clue if this 2-volt difference is a big one or not)..
Would anyone please gimme a piece of their mind on this issue?... Can this be a big deal or I am fine to go?
Btw I can change it back very easily, if this would be the wisest thing to do... It's just a matter of removing the USB-powered stick from the batteries spot and re-inserting the batteries.

Thanks,

Raphael
 
Last edited by a moderator:

Harald Kapp

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Nov 17, 2011
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Welcome to EP, Raphael.

Applying 5V to a 3V circuit is not a good idea. Obviously the keyboard's power supply is designed with some safety margin - otherwise you'd have the keyboard killed by now.

Anyway It may be a good idea to reduce the 5V from the USB port to a more manageable voltage (not current!). A simple 3.3V linear regulator is just what you need in this application, e.g. this one. Figure 4 in the datasheet (linked on the product page I gave) shows how easy this regulator can be connected.
 
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