I have one of those flash disk that plays mp3s. I noticed that when plugged into a usb port even without the battery, it can still play mp3 off of the usb power. Since I seen alot of devices for usb ranging from usb coffee warmer and usb battery charger (yes I seen them in person), I decided to slice open a usb extension cable that came with a flash disk, and I got 4 wires, a red, black, green, and white... I want to know what wire carries the voltage and if I want to make a battery pack what should I connect the battery to? I really dont want to drill holes or whatever in a mp3 player but that AAA battery doesnt last too long and I was thinking if I put like a D battery on it it should last like a month or something. would I need more than 1.5volts from a battery or am I better off having wires going to where the battery contact is and connect a big battery to that??
First of all, you can't really know what a wire does just by the color. The color of the wire doesn't influence the current that goes in it. There are some conventions that can help (in your case I would guess red= voltage (maybe 5V), black= signal ground, white=signal, green=general ground), but the only way to be sure is to get a copy of the USB protocol specification and it should be written on there what wire does what. Or you can you a voltmeter to test each wire and find which one is the power.
You should put as many D batteries as they are AAA batteries and you just have to connect them at the same place the AAA batteries are connected.
I would be carefull playing with your mp3 player, in theory what you want to do should work with no problem, but you never know...
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