Paralell port powered little device.
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,
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.
See also: www.piclist.com/techref/ios.htm?key=port
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