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Re: [SeattleRobotics] Re: important - Sensing beam from above

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  • warrenhb
    Since I sent the message below, I ve rethought this. I think that in order for the coil-on-a-magnet type of sensor to sense proximity of metal, you d have to
    Message 1 of 2 , Mar 2, 2001
      Since I sent the message below, I've rethought this. I think that in order for the coil-on-a-magnet type of sensor to sense proximity of metal, you'd have to measure the inductance of the coil by applying an oscillating signal and measuring its impedance at that frequency.
      To get such a sensor to generate a voltage, you'd have to be moving the sensor - it wouldn't show proximity to metal, but change in proximity. You could swing it back and forth over the edge and watch for a pulse as it crossed the edge.
      Another type of sensor uses the Hall Effect. This is an actual magnetic field strength sensor. By itself it can't detect the proximity of metal unless the metal is magnetized, but I think it is possible to add a nearby magnet so that the proximity of the ferrous metal concentrates the magnetic field strength enough to trip the sensor. Inexpensive Hall effect sensors are available with integrated semiconductors - you apply a power supply voltage and it has a digital output. Some of them have a threshold at a certain field strength - they trip one way when the field strength is sufficiently above the threshold, and trip the other way when the strength is sufficiently below the threshold; others trip one way when the field strength is sufficiently positive, then trip the other way when the strength is sufficiently negative.
      Some completely different methods:
              Use a small sonar device to watch the beam.
              Use a light bulb or LED to illuminate the beam, and a phototransistor or photocell to sense the reflected light. This is hard to get working right under any ambient lighting conditions. For your application, I would suggest a light-tight box over the beam to keep ambient light out of your sensors. In particular, flourescent lights flash on and off 120 times a second (if your power is 60 Hz) so that can interfere with your light sensors.
      Doug Bell
      ----- Original Message -----
      From: warrenhb
      Sent: Friday, March 02, 2001 10:54 AM
      Subject: [SeattleRobotics] Re: important - Sensing beam from above

      If your problem is the same as the one mentioned by Muharrem Ata, then I would suggest sensing the proximity of the metal beam using a sensor consisting of a coil of wire wound around a magnet. I have never built one of these myself, but I know they can be bought. They are used to sense the proximity of gear teeth to count them going by. I am cc'ing the Seattle Robotics Society - maybe someone knows where to get this type of sensor.
      I suggest using two such sensors, spaced exactly 12 cm apart, as far forward as possible. Compare the sensor outputs with an analog comparator connected to a digital input, or perhaps with two A to D converter inputs to your microcontroller.
      Doug Bell
      ----- Original Message -----
      Sent: Friday, March 02, 2001 5:57 PM
      Subject: important

      I am a senior year mechanical engineering student.I have a project at this semestre about an autonomous vehicle. This vehicle must move on a suspended beam(width:12 cm).I am looking for a sensor type that keep this vehicle on that beam. What type of sensor can do that job. But i have a restriction that does not permit any parts of the vehicle below the beam surface level. Somehow I need to sense the edge of the beam and direct the vehicle with the sensors perception. I got stuck at this point.please help me. Thank you for your interest.

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