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Quick question for EE guy, 5volt, USB, soldering, etc (solved)
spystyle:
Hello from Maine :)
I have an LCD photo frame, I get a kick out of those. I bought it for almost nothing because it didn't come with a plug and it's a little beat up.
It calls for 5 volts and 1.5 amps. I have 5 volt adapters in my box of AC adapters but none fit!
I also have a USB cable.
if I knew where to solder I think I could power the photo frame from USB :)
Care to give me a clue based on these pics?
I know one of these points near the plug is +5v and another is ground, but I don't know which one and I don't know if I'd kill the LCD if I solder it wrong-ly
Thanks,
Craig
Franco B:
I don't think USB will be an option as you only have ~0.5A to play with from USB.
What are the specs of the 5v adapters? as long as they provide >1.5A you should be able to hack one of those. You can determine the polarity using a multimeter.
I will let someone else who actually knows something about electronics to tell you where to solder :) You will most likely be soldering to two pads which come off that socket (not the mounting ones if thats what they are) but you need to know which is + and which is - as the pin can be + or - and vice versa for the barell
If it was me though I would take a look at the PCB and see if I could see any common paths to/from those which may point towards a ground.
Then again I would probably get it wrong and fry it so as I said, wait until someone who knows what they are on about chips in :)
Kevin Mullins:
--- Quote from: Franco B on July 07, 2010, 07:23:40 pm ---I don't think USB will be an option as you only have ~0.5A to play with from USB.
--- End quote ---
I'm no EE, but that was the FIRST thing that crossed my mind as well.
@500ma vs. 1.5A is a helluva difference.
spystyle:
Aha, so USB has 0.5 amps - that explains why my "laptop sata hard drive to USB" adapter has two USB plugs, to make 1.0 amps.
You can stack USB plugs to add amperage, apparently.
I think I need an EE guy as a neighbor :)
MonMotha:
You physically can stack USB plugs and add the currents, but it's totally against the spec the way all those stupid adapters actually do it. You only are supposed to get 100mA (0.1A) until you "enumerate" to the OS and request more. They never do that on the second plug. It works because most PCs don't have (or need) full per-port power management and tend to just limit each port to a little over the maximum.
Stacking them in parallel works in this case because you're pretty much guaranteed that all the USB plugs on a machine actually hook up to the same power supply internally. Don't try it with switch mode bricks. They'll "fight" each other as each one will have a slightly different regulation point. Linear bricks (the bigger, heavier ones with bulky 60Hz transformers) would be a bit more forgiving. I'd recommend just finding a single supply capable of sourcing whatever you need.
It looks like the two pads for the power jack connected together near the "side" of the jack are probably ground. That would be typical of a "tip positive" DC barrel. The remaining pin in the center is the positive input. You can probably just buy a suitable brick or use a "universal" one. It the picture frame is well designed, it'll tolerate a reverse polarity situation (though it might not work). Don't count on it being well designed, though.
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