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electromanj
01-25-2007, 10:16 AM
Hello, I am having a problem with interference. What I have is a bs2 counting·objects on a conveyor belt. The conveyor belt motor is controlled by a frequency drive. When the stamp is tested away from the freq drive it functions properly. When the stamp is installed in the panel it does not work properly. I am counting the objects with ir emmiter detector. I am counting cycles. When I have the stamp away from the freq drive and there is no objects to break the beam i get a count of 0. When I have the stamp close to the freq drive and there are no objects I still get a count. Any help would be appriciated!

Mike Green
01-25-2007, 10:26 AM
With any situation like this, the problem is probably electrical noise, either getting into the Stamp's power supply or coupling into the detector circuitry. What is your Stamp power source? How well is it isolated from the motor for example? Are you using shielded wire between the Stamp and the IR detector? What IR detector are you using?

electromanj
01-25-2007, 11:23 AM
The power supply is a "wall wart" that was ordered from parallax. The power supply is from the same source as the drive whether it is close or near. I should say that the distance that makes a difference is about eight feet. I am using shielded cable for the sensors. The sensors are a ir led and a phototransistor pair from radio shack. Thanks.

Robert Kubichek
01-25-2007, 12:02 PM
electromanj said...
The power supply is a "wall wart" that was ordered from parallax. The power supply is from the same source as the drive whether it is close or near. I should say that the distance that makes a difference is about eight feet. I am using shielded cable for the sensors. The sensors are a ir led and a phototransistor pair from radio shack. Thanks.


You are getting noise through to the stamp from somewhere....
I would try to isolate the stamp in it's own shielded and grounded enclosure inside the main
control panel.
I would also add extra filtering to the power supply or run seperate
supplies for each...
To see how much RF is being generated by the motor controller,
hold a scanner by the open controller, and scan the bands...

YOU WILL BE SURPRISED!!! http://forums.parallax.com/images/smilies/yeah.gif http://forums.parallax.com/images/smilies/jumpin.gif http://forums.parallax.com/images/smilies/yeah.gif

I did the same thing where I used to work with my Yeasu HT,
The electricians were surprised it was SO much, easily detectable from over 50 feet away! http://forums.parallax.com/images/smilies/smilewinkgrin.gif


Bob N9LVU http://forums.parallax.com/images/smilies/scool.gif

ccevt
01-25-2007, 12:03 PM
electromanj,

Start by cutting the problem in half. To determine if it is noise on the power supply, try to power the stamp and associated circuitry with a suitable battery (9V?) with short leads. If that works, then you need power supply filtering (either on the AC line or DC output). If that does not solve the problem, then you must be picking up noise on one (or more) of your I/O lines. Make sure your circuits are not in a strong magnetic field of a motor or transformer. Grounded ferrous metal shielding could help control magnetic fields.

N1HC

electromanj
01-25-2007, 09:29 PM
Thanks for the tips I'll try them and see what happens.