A couple of other thoughts. These sensors only have a range of 80cm so unless you have a pretty tight stairway you're going to have difficulty detecting across the entire stair. 60 feet of CAT5 is going to pick up quite a lot of power line hum. That's may be the low frequency noise you're seeing. You may want to re-think how you transport your signals. Personally I'd put a microcontroller at each sensor end and try to send the signal using a more rugged scheme such as CAN. Or maybe use advantages of the CAT5 differential pair to transmit a balanced digital signal of some kind. Are you using any power supply filter capacitors near the sensors? That'd be a start. I'm not sure what the resistance of 60 feet of CAT5 is but it's probably more than you'd like. The result of this will be that the sensors will communicate dirty power to each other more than they would on a shorter wire. If you have an oscilloscope have a look at the power at the sensor end. If it's full of spikes and flops around a lot add some filter capacitors at each sensor and/or try supplying each of the sensors from different conductors on the CAT5. 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