GP2D12s send out a continuous stream of infrared. When two of them can
"see" each other's beams interference occurs. The solution is to use a
different model such as the GP2D02 which allows you to sample on
demand.

Here's a piece from the acroname web site:
"The GP2D12 and GP2D15 ... fire continuously and don't need any
clocking to initiate a reading, they are easier to interface but use
more power and can potentially interfere with one another when
multiple detectors are used on a single robot.  Interference can be
avoided with the GP2D02 and GP2D05 because the microprocessor can
control when they fire."

http://www.acroname.com/robotics/info/articles/sharp/sharp.html#s4

Incidentally I got caught by this one too. I'm now using GP2D02s.

Cheers,
Zik

On 04/06/06, Darren Gibbs <tsquank@yahoo.com> wrote:
> I wonder if anyone could help with an insight into this situation...
> I'm out of my debugging depth at this point.
>
> I'm working on a project with several remote sensors.  On each of 4
> flights of stairs there are mounted two Sharp GP2D12 IR distance
> sensors (pointed lengthwise to detect a stepping foot anywhere on the
> monitored stair) and a KC7783 IR motion sensor to detect activity at
> the doorways.  Both of these parts operate at +5V and are connected
> to to a 5V 5A power supply.  The distance sensors output an analog
> voltage (2V range), and the motion sensor TTL.   The distance sensors
> draw 33mA each and the motion sensor 400uA.
>
> When the three sensors are all connected near (within a foot of) the
> power supply, they all work fine.
> When connected at the end of about 60' of CAT5, the motion sensor
> refuses to work and I see low frequency noise on all three sensor
> outputs.
> If I power the motion sensor right at the 5V supply, but leave the
> distance sensors at the far end of the long cable, they all work fine.
> If I leave the motion sensor at the far end of the cable, but power
> the distance sensors right at the supply everything works fine.
> If I leave all three sensors at the far end of the cable, power the
> distance sensors right where they're mounted using a 9V battery +
> LM7805, and power the motion sensor from the 5V supply at the near
> end of the cable, all three work fine.
>
> The only non-working configuration is all three devices at the far
> end of the cable, with all three powered through the cable.
>
> I'm wondering what the distance sensors could be doing to the power
> supply from the far end of the cable that would cause the motion
> sensor to crap out, but not have that effect on the near end of the
> cable.  Is there something about running the power to those device
> through the 60' of wire that would make such a difference?
>
> Any suggestions much appreciated!
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