Hmmm... I didn't catch that on the website, but I don't think that's what's going on here. The two distance sensors are fixed and pointed in opposite directions on different levels of the stairwell between 3 and 10 feet apart vertically (different on each flight of steps). The two Sharp parts seem to be working fine themselves, I get good measurements from them... it's just that having them powered from the same supply as the motion sensor causes the motion sensor to not work. When I hook up a scope to the +5V lead at the far end of the cable, it looks beautifully flat when nothing is connected. When I connect a Sharp sensor, I start seeing 1V dips every 1ms. Same thing when two are connected. I also see ~1V pulses on the signal output every 1ms. The data sheet says the Sharp parts update every 32ms, maybe they're sampling every ms and averaging? I thought maybe the 1ms illumination pulses were pulling down the supply, but if the IR shines continuously that doesn't make sense. On Jun 3, 2006, at 5:49 PM, Zik Saleeba wrote: > 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 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! >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist