Photoelectric Detector

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Photoelectric Detector

• ECE 4894
• Section RPY
• Date July 26, 2004
• By Scott Groves

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Photoelectric Detectors

• Commonly used in todays home alarms systems
• It implements a laser and some type of
  photo-sensor

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Photoelectric Detector

• The laser shoots a beam to the photo-sensor
• If beam is disrupted, the sensor sends out to a
  signal

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Experiments

• I chose the LTS1 for my project
• Several experiments were performed
• First surrounding light was greatly increased.

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Experiments contd

• Next an extra laser was used to see if the sensor
  could be manipulated

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Results

• Increasing the light had no effect on the device
• The additional laser aimed at the device did make
  it possible for the original beam to be broken
  and not set off the alarm

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Photo-sensor

• There are several types of photo-sensors
• Phototransistor
• NPN Transistor
• Collector, Base, Emitter

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Phototransistor

• The phototransistor acts like a switch
• Light (photons) strikes the Base tuning it on.
• When the beam is broken, the switch is cut off
  and power is routed to the alerting circuitry and
  trigger relay

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Characteristics

• Spectral Response 630-670 nm
• Linearity 3 to 4 decades of illumination
• Sensitivity area of the base and the dc
  current gain
• Dark current current that can flow from the
  collector to the emitter and the transistor still
  be off 10nA to 100nA

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Modifications

• Make an enclosure that completely surrounds the
  photo-sensor so that a laser has to be at a
  precise angle to hit the photo-sensor. That way
  no other laser sources can be used.

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Modifications contd

• Make mirrors standard so that the laser beam can
  be projected all the way up a doorway so that
  someone cannot just step over the laser beam.

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Any Questions?
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References

• http//www.physlink.com/Education/AskExperts/ae430
  .cfm (Visited 2004, July 20)
  
• http//www.tpub.com/neets/book7/26g.htm (Visited
  2004, July 22)
• http//www.ramseyelectronics.com/downloads/manuals
  /LTS1.pdf (Visited 2004, July 17)
• http//optoelectronics.perkinelmer.com/catalog/Pro
  duct.aspx?ProductIDVTT3323LA (Visited 2004,
  July 25)