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Building A Light Curtain?

  1. Feb 22, 2010 #1
    http://www.machineguardsolutions.com/images/lightcurtain2.jpg [Broken]

    A light curtain seems like a basic communication system setup (TX & RX).
    But what kind of signal are you trying to send and receive? How should the receiving end get processed?
    How do you deal with crosstalk from using multiple transmitters and receivers?
    What is the best way to deal with aligning the IR transmitters and receivers?
    How far of a distance can IR leds transmit?

    I don't know much about IR technology as well as this particular application. So, any information or direction on the topic would be greatly appreciated. Book, articles, anything. I've been trying to search the internet but I am having a hard time finding material.

    Thanks.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 22, 2010 #2

    berkeman

    User Avatar

    Staff: Mentor

    Welcome to the PF. Here's a basic intro article (pretty light on technical details):

    http://en.wikipedia.org/wiki/Light_curtain

    I didn't realize there are some published standards for light curtains. I guess because they are sometimes used for protecting users against dangerous machinery.

    And an example of a LC manufacturer (you probably already found this one):

    http://www.lightcurtain.com/light_curtian-selection.html [Broken]

    In general, you would time multiplex the rows of the LC, to give you better spatial separation. Maybe spend 10ms per row or something. You'd also pulse modulate the IR transmission signals, probably at about the same frequency as IR remote controls (39kHz? I may not be remembering that right, but it's easy to check). You do that for ambient noise rejection.

    You can also add collimation optics in the IR, so that you are using the energy from your IR emitting LEDs the most efficiently. What LEDs and receiver circuits are you planning on using? What is the application? What is your background?
     
    Last edited by a moderator: May 4, 2017
  4. Feb 28, 2010 #3
    Thanks for the reply, berkeman. Sorry, for the late response I have been busy with school.

    36kHz is typically used for remote control applications. (Anywhere from 30-60kHz)

    I have yet to pick out the IR transmitter and receiver circuits because I have never dealt with IR before. So I've been trying to read up, and see if it will work with the application that I had in mind.

    The overall project is an automated greenhouse (control lights, temps, moister, ect.), the light curtain should be mounted a 1 ft below a series of 4ft fluorescent bulbs. The idea is whenever the IR light curtain gets triggered due to the plant's growth, the lighting rig will adjust keeping that fixed distance of 1 ft. between the fluorescent and the plant.

    The issue is the need for multiple IR transmitters and receivers that will cover a 4ftx2ft area. I figured it should be generally easy to setup on the receiving end using a basic summing amplifier that is fed into an integrator circuit. But then can that same concept be applied with time division multiplexing? That means the receiving end will only be seeing only one of the many transmitters for a certain time interval, does that mean I should be basing my response off of the single receiver. Also, would it be better to buy transmitters and receivers that operate at different frequencies vs. creating a timing circuit for each transmitter and receiver?

    Also, my background is that of an electrical engineering student with a basic mix of theory and some simple applications.
     
    Last edited by a moderator: May 4, 2017
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