Help with photointerrupter

Discussion in 'General Electronics Chat' started by Clambake, Jan 23, 2012.

  1. Clambake

    Thread Starter New Member

    Jan 23, 2012
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    Hi
    I'm new here, and not at all knowledgeable about electronics, so please bear with me.

    I have an electro-mechanical project I am working on. I have multiple potentiometer controlled voltages (up to 5VDC) being triggered (hopefully) by reflective photointerrupters (Everlight ITR-20001s). Unfortunately, I am fuzzy about how they should be wired. The pins are labeled:

    Annode
    Cathode
    Collector
    Emitter

    Does anyone here have any suggestions for my (likely extremely simple) problem? I'm hoping to use the photointerrupters as simple switches -run the varible voltages directly through them to the unit's output. Can I do this?


    http://www.everlight.com/datasheets/ITR20001-T.pdf
     
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Can you explain more clearly what you are trying to do? In particular, what do you mean by voltages being "triggered"? Selected perhaps?

    A schematic of your proposed circuit would help.

    In principle, more accurate results might be obtained by using these proximity detectors to control other devices such as analogue switches to perform voltage selections.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    ClamB: Awesome, a direct link to the part you are interested in. Well done! Sorry I'm on my way out and only have a bit to respond right now.

    The anode/cathode are to connect the LED light source. A resistor from the +5V will run that side just fine.

    The problem comes with the other side. Collector/emitter is a transistor that the light turns on when it is passing thru the window (an object blocking the light turns the transistor off).

    The tough thing here is we have no idea what you are trying to control with this signal, so give us a bit more info, OK?
     
  4. Clambake

    Thread Starter New Member

    Jan 23, 2012
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    Adjuster: yes, selected is probably a better word. I also understand what you are saying about preferably using the interrupter to control another switch. I was hoping to use the interrupters themselves seeing as an extremely small amperage output is needed. I'm currently experimenting with 0.7mA (5VDC) now, could probably go lower.

    Ernie: I am building a mostly mechanical synthesizer sequencer. It's output will be varying voltages (from 0 to 5VDC) at very low amperage to cause an old analog synthesizer to play various notes in sequence. It will use 36 50K Ohm potentiometers selected by 36 (preferably reflective optical) interrupters, triggered one at a time by a single motor-driven variable rpm rotary trip.

    I hope that helps clarify things.
     
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    It seems likely that using the simple method you describe would give poor pitch accuracy. The optical devices you have chosen will not give the sort of "snap action" which I assume you would wish for.

    My guess would be that this would result in a sliding transition (glissando?) to each new note, and the even the settled pitch of the notes may not be stable. Processing the outputs from the detectors by for instance a set of Schmitt triggers might obviate this. Unless of course a sliding noise is intended.

    What is the ultimate aim - are you trying to electrify an existing mechanical instrument, such as a barrel organ?
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I think I would try it. A 4N25 worked well in simulation when the pot wiper was on the emitter, with the output on the collector. However, I was driving the LED with around 20mA. It might not work with a reflective interrupter because the received light level will probably be low, resulting on low transistor collector current.
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
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    That would be my worry. Unless the optical contrast was good enough to saturate the transistor when it was intended to be on, and just as importantly cut it off completely when intended to be off, the tuning might be poor.

    For an analogue pitch control voltage, errors of a percentage point could be pretty serious: as I recollect, a semitone only comes to about 6%.
     
  8. Clambake

    Thread Starter New Member

    Jan 23, 2012
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    Adjuster: The ultimate aim is a sequencer to run an old analog voltage-controlled synthesizer. Basically like a player piano, but modifiable real-time.

    I would rather not have a sliding transition OR unstable notes -I can create that on the synthesizer if I need it. Do you think these Schmitt switches would be best?
     
  9. Adjuster

    Well-Known Member

    Dec 26, 2010
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    I think that before we go too far a more complete description of the sequencer mechanics would be a good idea.

    In principle though, I think there would better not be any link between things like say the colour of the recording material and the pitch of the notes.

    The idea of a set of Schmitt triggers (gates, or maybe level comparators) was my first guess at this. More modern workers would probably throw the whole thing into a micro-controller of some kind. I would say that begs a question though, namely why are you getting the sequence from a mechanical system in the first place, rather than say a computer. Are you using rolls made for a player piano?

    Edit: 2am London time now. Time for bed!
     
  10. Clambake

    Thread Starter New Member

    Jan 23, 2012
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    Sure
    My old monophonic synthesizer is voltage-controlled. It has a 1/4" CV/pitch input jack in the back that disables the keyboard so the pitch is completely controlled by the voltage sent through that jack.
    My plan is to build a sequencer to send various voltages at various speeds through that jack. Being more mechanically inclined than electrically, any machine I design and build naturally will be more heavily dependent upon the mechanical than the electrical. My plan is to have an array of switches triggered by a simple motor-controlled trip. When tripped, each switch will allow the voltage from it's potentiometer to exit the sequencer and create a note in the synthesizer. It is an extremely simple machine, and I am very aware that more could be done with a computer, or even an off-the-shelf sequencer. I guess it may be difficult to understand why I would want to build something so limited, but that's what I want to build.

    Perhaps I need to put a relay between each interrupter/potentiometer?
     
    Last edited: Jan 23, 2012
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What is going to be blocking the photo interrupters? If it is semi-transparent, there will be some leakage, and on time won't be instant, as whatever is moving across it will cause it to be halfway on at some point.

    Smaller aperture interrupters help, even laser types, but they are expensive.
     
  12. Adjuster

    Well-Known Member

    Dec 26, 2010
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    I think that you might struggle to get relays to be be triggered directly from these photo-interruptors. Probably some kind of trigger circuit is needed first, then to be followed by relays, or analogue switch ICs.

    It would be possible to continue with a long discussion of methods which might or might not work, but this can't be very conclusive in the absence of hard information. What is needed here are some numbers on how well the photo-interruptors switch in your set-up. Perhaps something as simple as a 9V battery and maybe a 10kΩ in series loading the photo-transistor would give you an idea - have you got a scope, or at least a DMM?
     
  13. Clambake

    Thread Starter New Member

    Jan 23, 2012
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    Well, I'm thinking maybe I should just go with roller switches -I'm sure those can do the job by themselves. Thanks for helping me make a better decision!
     
  14. 3DTraveler

    New Member

    Feb 10, 2012
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    I was wondering if anyone might be able to help me adapt a Schmitt Trigger Photogate circuit (the one at http://hiviz.com/tools/triggers/makeown.htm ) to use a reflective photo interrupter.

    The application I have in mind would trigger a camera's shutter release at regular intervals, like every 1/4", or every 1/2". I'd like to just print out a strip of black and white stripes, like a barcode, and have the shutter triggered every time the photo interrupter passes over a white (or black) stripe.

    So, what I need is a recommendation for a focused reflective photo interrupter that will work in the circuit (like the Honeywell HOA0149), and help with adapting the circuit to handle the requirements of whatever photo interrupter you might recommend. Also, if you have a relay in mind that would let me use the circuit's output to trigger the camera, that would be a big help too.

    By the way, the reason for the setup is to take a sequence of images at regular intervals. A series of 9, 18, or 36 images is then aligned and interlaced using SuperFlip! software to make a 3D lenticular print.

    Obviously, I've not much of an electronics person, so I would really appreciate any help you might care to offer.
     
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