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| How best to get 5v power for push button lamp? |
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| DaOld Man:
--- Quote from: misbehavens on April 12, 2012, 08:10:34 pm ---Again, this is a laptop powered control panel. I will have an extra USB port available. This would be easiest if the port provides the correct power. The power requirements listed on the website say 100ma @ 5v DC Per button. I only have one button. Someone mentioned that USB ports do 500ma max. Does that mean USB would suffice for this scenario? If not, does that mean I need to run power to my control panel? I'm assuming I can take an old USB cord, cut it open and tap into the black and red wires and use that to power my button. Am I assuming wrong? What else would I need to do to make this work? Also, the tapping into 5v header on the I-PAC sounds like a good option too, as long as it is appropriate and will not damage the board by doing something it was never intended to support. Thoughts? --- End quote --- The usb should power that ONE LED. It must be a pretty bright LED to draw 100MA. The wall wart that smeghead suggested would probably be safer for the PC, if you have room for it. Once again, I have no experience on the I-Pac, so not sure if it will supply 100 MA or not. |
| misbehavens:
Here's what Wikipedia had to say about USB power: "A unit load is defined as 100 mA in USB 2.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0. There are two types of devices: low-power and high-power. A low-power device draws at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0. A high-power device draws the maximum number of unit loads. Every device functions initially as low-power but the device may request high-power and will get it if the power is available on the providing bus." It sounds like the USB port will only provide 100mA by default anyway, so I think for the purposes of this button, hacking an old USB cord will suffice for now. However, if I ever plan to add more lights in the future, I now have some ideas of how to do it. Thanks everyone! |
| DaOld Man:
If anything weird happens, such as random PC reboots, I would discontinue use, but I honestly think it will be ok. |
| AndyWarne:
--- Quote from: misbehavens on April 13, 2012, 02:08:09 am ---Here's what Wikipedia had to say about USB power: "A unit load is defined as 100 mA in USB 2.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0. There are two types of devices: low-power and high-power. A low-power device draws at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0. A high-power device draws the maximum number of unit loads. Every device functions initially as low-power but the device may request high-power and will get it if the power is available on the providing bus." Thanks everyone! --- End quote --- Thats actually incorrect. The 5 volts on USB ports is not controlled by the PC and the device has no ability to request the PC to supply more current. The 5 volts is connected directly to the PC power supply. 500mA would easily be available. The way it actually works is USB devices tell the host how much power they use and the host keeps record of this and will display a warning if there is more than 500mA requested, but the host does not actually control the power available. |
| Smeghead:
I just wouldnt even bother, with everything else plugged in its so easy to exceed the USB power available |
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