DIY USB Y-Cable ?

M

MindBuster

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I want to power a digital picture frame from usb and got it working, sorta, when it's just showing a pic everything is fine, but when it transition from one pic to another I get some flickering, as if it doesnt get enough power (it does the job though, I just dont like the flickering).

It comes with a 5VDC 1000Mah wall-wart, the back of the frame says it draws 4 watts.
First I tried just powering it from USB 5V+ and GND, which didnt work, it didnt boot, as USB only supplies 100Mah, up to 500Mah when requested for it, but the frame has no way of telling what it needs.

Then I put the port in "Charger Mode" by shorting the two data lines, which work, except for the flickering when changing pics.

So I want to make a USB Y Cable, to get power from two ports, and was wondering if it's as simple as just combining 5v+/5v+ and gnd/gnd. or do I need some sort of diode on one of the 5v+ lines ?

Also, is the shorting of the data lines I did, safe enough, or do I need something in between those also ?
 
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You could try it, but I know I personally wouldn't. Putting series diodes on each line will ensure one doesn't drive the other, but also means you'll be getting less voltage to the display. I would also recommend that you at least put a resistor between the data lines, so that again, one doesn't damage the other. You'll have to test several to find the largest resistance that will still work.
 
Mohonri said:
You could try it, but I know I personally wouldn't. Putting series diodes on each line will ensure one doesn't drive the other, but also means you'll be getting less voltage to the display. I would also recommend that you at least put a resistor between the data lines, so that again, one doesn't damage the other. You'll have to test several to find the largest resistance that will still work.
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Yes, I'm uncomfortable doing it also.

What about putting a diode on one of the lines only, one line without that supplies the needed 5v, and a diode on the second that may not give the full 5v but atleast gives some extra amperage ?
Or maybe it doesnt work that way, dunno if the "dioded" line would just drag from the other, even things out, like if the line without diode gives 5v and the dioded line gives 3v, then end result would be 4v ? :p
Or would it be 5v with added power ?

And dunno what kinda diode to put in there in the first place.

As for the resistor on the data lines I guess I'll have to wait until I get myself a multimeter, though I found something about it, suggesting a 220k ohm resistor, dunno about that though.
 
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Nah, you definitely need diodes on both, not just to prevent one from backfeeding the other, but also to make sure the outputs are at the same voltage level.
 
why not break out the drill and tap into your pc's 5v rail, use a molex adapter, even the fan type would be fine. get an plug for your case, and red+black wires are what you are after. diodes on a 5v supply will eat up too much voltage, even if you use schottky diodes
 
ryuji said:
why not break out the drill and tap into your pc's 5v rail, use a molex adapter, even the fan type would be fine. get an plug for your case, and red+black wires are what you are after. diodes on a 5v supply will eat up too much voltage, even if you use schottky diodes
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It's for external use using my netbook :p
 
You shouldn't have a problem with a Y connector from two USB ports. I have a couple of 2.5" hard drives that use two USB connectors, one for power only and one for data/power. One of the problems is USB cables usually have relatively small wire in them, increasing the resistance enough to hamper the power delivery. USB ports also have an internal current sensor and will disable themselves if excess current is drawn. Don't worry about he two ports fighting each other, it's not an issue. Don't use a diode, too much voltage drop. If possible, find a "Y" adaptor for 2.5" hard drives and use the largest wire you can. And the resistor connecting the data pins is a good idea too.
 
Cheaper alternative: [ame="http://cgi.ebay.com/USB-Dual-Power-Y-2-x-Type-Mini-B-Cable-Lead-Wire-/110684426611?pt=LH_DefaultDomain_0&hash=item19c54e5173#ht_3052wt_1135"]USB Dual Power Y 2 x Type A To Mini B Cable Lead Wire | eBay[/ame]

It'd be more expensive to gather parts and take the time to solder it, provided you don't have parts lying around ;) USB Y cable on ebay will net you different results if you are looking for different connector types.
 
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