Replace the Battery on a Desktop Gadget With USB Power





Introduction: Replace the Battery on a Desktop Gadget With USB Power

About: I like to make stuff and to make things work my way.

I have a set of noise cancelling headphones at work. The active part does a nice job on the building ventilation and computer fans, and the passive part on my co-worker's phone conversations. I didn't like the idea of wasting batteries, though, and the system didn't seem to like even NiMH rechargeables. So, I decided to run them off the USB port.
The USB port can supply 5V, but I needed the ~1.5V that a single AAA will supply.

I have used this setup for about a year now, and it works fine. If I had to re-do it, I would make sure that the wire lenghts for the original gadget wire and the power/USB wire match so you can tape the boxes together. Same goes for the direction in which the wires exit the box.

Step 1: Figure Out the Circuit

I used an LM317 voltage regulator and two resistors (100ohm and 470ohm) to get the right voltage. I used the USB cable from an old PDA syncing station for the input. The breadboard shows the layout, I don't have a wiring diagram.
If you have not worked with a breadboard before, you stick the parts into the holes, and the holes are connected to each other in rows perpendicular to the long axis of the board.
Please see the image for further instructions.
Measure your USB cable to find the ground/"-" and the positive.

I took the picture from several different angles, but could not find one that really made things clear. I hope the image notes do.

Step 2: The "Battery"

Turns out a large hardwood dowel is just the right size to make up for a AAA battery, once you add a wood screw at each end as the battery terminals. I pre-drilled and screwed in a short screw all the way on the "-" side, holding down that wire. I then screwed in a longer screw on the "+" side and cut it off at about the right lenght. Final adjustments to length can be made by turning the cut-off screw in or out.

I only needed one battery for this project, but if you needed several, you could make dummy cells from a screw or nail that goes right through a dowel...

Step 3: Make It Permanent

You don't really need this last step, but I wanted to enclose the project and to have my breadboard back. I soldered the same circuit onto a piece of project board with the same layout as the breadboard. You could probably just solder things straight together if you don't have any project board around.
I used an old chewing gum tin lined with electrical tape where it matters and some rubber grommets from an old hard drive to protect the wires from sharp edges on the metal. .



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just used these instructions to power an mp3 player i use in my car, very useful.

of course u can do it without a dammy battery but its ok....thans

I applied this instructable to a FM transmitter I have, and I love it! The only thing I changed, was that I hard wired the "battery", instead of creating a dummy. Thank you so much for writing this!

idk much about writing drivers or any programming for that fact, but you think it would be feasible to control this (or other usb toys like it) with the pc? where to find some kind of gui driver would be nice lol.

Question: according to this diagram, the Gnd and Vout are connected, so what is the point of the 470 ohm bridging them ? It's like the + battery connects to the 100ohm, no ? I want to get this clear before I hookup something that might fry my pc...

5 replies

Oi, that;s a long time ago! I suspect you found an error in my diagram.

Obviously it would not make sense to have the resistor parallel with that direct connection. If you have this set up on a breadboard, I would suggest trying to hook it up as described in the picture minus the direct connection.
One other option would be to download a spec sheet for an LM 317, mine came with the circuit and explanation.

Sorry to pass the buck. I will try to have a look at the real thing tomorrow at work. All I can tell you right now is it's still up and running fine.

As for frying your PC... better to be safe than sorry, but the USB protocol is supposed to be pretty self regulating as far as I know.

Wow, thank you so much for that . Since my understanding or electronics is limited (i can follow a sketch and solder basically) I'm hoping you can confirm the sketch I sent (maybe update online). Also, in the worst case scenario, if I short something out, did you say it will not fry my motherboard and all the rest ? is there a fuse or protection somewhere ? Again, thank you for your time and reply.


Hi Yanivn,
I think that circuit is right. Have a look at the spec sheet for the LM317 too, e.g. here.
As for the safety of a USB port, I really in the end don't know enough about them to be sure. However, wikipedia about USB non std devices looks reassuring. If the power to a port is limited to 500mA, that should take care of a short-circuit, should it not?

I guess so. But to be sure, I bought a voltmeter ... Thank you very much. Y

Hey, If I gave someone an excuse to extend their tool collection, I have done my job. :-)

For those who decide to try this, remember a USB port can supply 500 mA at the most.

I love the battery Idea.


Good Instructable, The wooden dowel to emulate a battery is a great idea. I'd recommend taking the time to create some sort of circuit diagram, in case anyone unfamiliar to electronics wants to have a go at this. This would be ideal as a first electronics project, being simple AND very useful.

1 reply

Yes, I was being a bit lazy there. I added a diagram now, though it probably doesn't follow any conventions :-). Has anyone else noticed some of the instructable editing being really slow now? Thanks for the feedback!