[PD] PD, arduino and sharp range detectors

[Martin Peach]

Tim Boykett wrote:
>    We are having trouble with a PD - Arduino - Sharp IR gp2d12 IR
>range sensor.
>
>everything works for a while, then the arduino just stops and sometimes
>takes PD down with it. once we had a warning from the OS that there
>was too much current
>being sucked on the USB port.
>
>we are using three such things, each uses typically 33 and up to 50
>mA. This
>should (according to the Arduino and USB specs) not be too much, but
>perhaps
>these are wrong.

I have built a circuit with six of those sensors on an Arduino Diecimila, it 
worked fine with external power, but I didn't even try it with USB power 
because for me 50mA is too much. (At first it crashed sporadically because I 
was sending too much data through the serial port.) The actual USB port you 
are using may not be able to supply that much current even if the USB 
circuit is able to handle it. If it only happens occasionally it's probably 
because the sensors sometimes pull more than the average current, so a 
~100uF capacitor on the power pins would help, but you should really use a 
separate power supply for the sensors, or just power the entire Arduino 
externally.

Martin