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netcoord said:I have a mini fountain that runs on 2 AA batteries. im tired of buying batteries for it so i was thinking itwould be pimp to mod it in to a usb device. any one have a idea how to go about doing this.
thanks
LOL no. First of all a resistor is a bad idea for this. Second of all resistors aren't rated by voltages. They're rated in Ohms (resistance) and watts (power). For simplicity - you could probably just put 3 rectifier diodes in series. a 1N4007 (well anything between 1N4001 and 1N4007) Would be perfect. Current would probabaly be low enough to use small signal diodes - like the 1N914 - again you'd want 3 in series. Either should work just fine though - and I'd expect any electronics store (even ratshack) to have at least one of them, probably both. Hope this helps.netcoord said:it would be cool to control it but my main concern is power
thanks
so i would put a inline 2v resistor on the power wire in the usb and atach it to the the positive wire for the motor of the fountain. the atach the usb ground to the motor ground.
Teancum said:If you want to use a resistor, what you need to know is the current draw of the fountain. Then take 2V/current = size of resistor.
I diode will not necessarily be better than a resistor as far as power dissipation goes. The same amount of current will still drop the same amount of voltage, so the dissipation will still be 2V * current. The advantage of diodes is that they drop the same amount of voltage regardless of current (within a certain range), so you don't have to worry about calculating resistances.
grjr said:I don't think I understood a single thing you said
fat-tony said:Let me try to clear it up. Instead of having a resistor to drop the 2V, we instead want to use some diodes:
Each diode drops roughly 0.7V, pretty much independant of the current through them, so you don't have to do any calculations to try to figure out the size of them, like you would with a resistor. They provide a pretty steady 2.1V drop no matter what load is on them (within reason).
wayne said:check the current draw... thats pretty much all i can say
also, some guy had a link or something that shows the current that USB ports can supply up to
whats a diode for and what are you using it for?
Well, not blowing up the mainboard's USB-headers, for one thingGlobalFear said:Whats the fun in that?
That would also mean connecting the fountain's pump to the PC's PSU. It would certainly make more sense than (ab)using an USB port for this purpose.GlobalFear said:Anyways look up a few posts. I posted a different idea.
kronchev said:mini fountain? more info on this. I think I want to put this in my case too