Author Options:

USB to Travel Clock Circuit Help :) Answered

I've got this little black Oregon Scientific travel clock thing with a transparent screen. It was an old gadget of grandma's I found years ago. I was eying it, and I had a damn good idea for an Instructable-worthy project. I'd eventually like to run this off of USB power. Currently it has a little button-battery in it (Energizer 357, bout 1CM in diameter). I know USB out is an unsteady 5V, so I'd need a capacitor to regulate the current, I guess, and the necessary circuitry to adjust the voltage to whatever this little clock runs on. Any advice for such a novice?


I don't know, just a thought, maybe instead of a capacitor, you could use a voltage regulator to output 5 Volts.

to use, say a 7805 (5 v regulator) you need a power supply voltage that can be unreglated DC 8-18V but it can not drop below the 8 v minimum and continue to function.

You could, however, use a variable voltage regulator like an LM317, to get any voltage between 1.25 - 2V, from a 5V input voltage. Probably overkill. Then again, I don't know how noisy a USB power supply is, or how sensitive a clock circuit would be to those fluctuations.

A simple voltage divider might work. Find the current taken by the battery.

The battery is dead, and I'm not really sure how to measure the draw from the clock. I do indeed have a multimeter,

. FWIW, that's a 1.55V silver oxide battery

Well, obviously you need the help of some people more experienced with such things. I'd try a community like that on instructables.com, and I-- Oh, nevermind, you found us already.