piclist 2000\06\05\203020a >
Thread: Paralell port powered little device.
www.piclist.com/techref/ios.htm?key=port
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face BY : Mark Willis email (remove spam text)



Edson Brusque wrote:
> Hello all,
>
> Arthur Brown wrote:
> >Why not take the power from the keyboard conecter or a games port
> >40Ma from the printerPort is not easy to do, as some motherboards use open
> >collecter outputs if you reduce your Ma request you could take a small
> >voltage from unused datapins at the lower ttl high voltage.
>
>     Take power from the keyboard connector seens to be the option. I could
> make an adapter using a pair of din connectors and take the signals from pin
> 4 (GND) and pin 5 (+5VDC/VCC) to power my little gadget. What about using a
> pair of resistors (say, 47R)in series with the GND and VCC to limit the
> current in case of short-circuit?
>
>     Best regards,
>
>     Brusque

Why 2 resistors?  And why 47R (1.88V drop at 40mA - Apiece!)

I'd suggest perhaps 10R instead, 0.4V drop at 40mA, but then your Isc is
0.5A and your keyboard fuse probably will be safe.

 Mark

<393C45A6.B75D65E2@foxinternet.net> 7bit

See also: www.piclist.com/techref/ios.htm?key=port
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