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Is my IR photo interupter dead? Can you test them

Discussion in 'General Electronics Discussion' started by apples, Jan 25, 2014.

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  1. apples

    apples

    97
    2
    Jul 1, 2012
    I am tinkering with an optical IR photo interupter that I have found on the back of some small motors.

    The IR LED works as I can see it using the video camera on my phone. But for the life of me I can not seem to get any signal from it.

    The problem might be me as I am new to this, but with it all hooked up (only 3 wires) +, - and signal. Not much happens. The light turns on but what is the green signal wire on this thing supposed to do?

    Is it just like a switch, I tried to measure any voltage between this green signal wire and the -ve and nothing. Then I plugged in a normal LED with the correct value resistor to see if it would light up etc, nothing.

    I have given this 12v . Might have been too much, who knows. No pops or escaping smoke was observed :)

    So can I test just the IR receiver part at all?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,522
    2,654
    Nov 17, 2011
    Tell us the part number you're dealing with or post at least a photo. There are many kinds of such sensors.

    Chances are you need an amplifier because the receiver is a photodiode or phototransistor with only a weak signal.
     
  3. apples

    apples

    97
    2
    Jul 1, 2012
    Part number I get : 7STS-04
    94v-0
     

    Attached Files:

  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Did you try blocking the path and see if that made a difference on the signal line? It is possible that the signal goes high when it is blocked.

    Bob
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    11,522
    2,654
    Nov 17, 2011
    94V-0 is an UL marking of the PCB, not relevant for the function of the sensor.

    The number 7STS-04 doesn't tell me anything, sorry. The build is similar to this one (just an example), only that a resistor for limiting the LED current seems to be built into the sensor and obviously one common connector is used (that's why there are 3 wires, not 4).
    Anyway, the phototransistor will need additional circuitry to deliver a useful signal. Here is a collection of possible circuits (may need to be adapted to the component you have at hand).
     
  6. apples

    apples

    97
    2
    Jul 1, 2012
    What signal will it give? enough for my arduino to pick it up? I have a scope, would that pick it up?
     
  7. apples

    apples

    97
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    Jul 1, 2012
    This is how I have been trying to measure a voltage signal with my multimeter.
     

    Attached Files:

  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Place a resistor (1k, 10k?) in series with the collector and measure the voltage across that. Leave the base totally disconnected.
     
  9. davenn

    davenn Moderator

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    Sep 5, 2009
    it wont give anything till you incorporate it into the rest of the receiver circuitry like Harald linked to
    The photo transistor is just a collector emitter junction that is turned on when light falls on it. that is, its nothing more than a light operated switch

    no, look again at the second link Harald gave and all the examples

    Dave
     
    Last edited: Jan 26, 2014
  10. shumifan50

    shumifan50

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    57
    Jan 16, 2014
  11. apples

    apples

    97
    2
    Jul 1, 2012
    Ok update:

    I have now set up a 2N5551 NPN transistor.

    2.94v supply from battery pack
    correct resistors for yellow LED, it works fine.
    resistor for base of transistor wanted to be 980ohm for about 3mA only had a 1K.

    I have drawn in the three wires on the IR photo transistor to the corresponding pins that are on the part.

    1. If I connect the grey wire to the +ve rail, then connect the green wire to the Base the yellow LED lights up. It also does it when I swap the green wire for the white wire, with the grey still on +ve.
    What does this mean? I am assuming that the IR sensor is normally off, or when there is no light present. Then when the light hits it, it would allow the flow of electrons. So if in my case now it always seem to flow could it be damaged?

    2. How do you tell if this IR photo transistor is fried? What are they symptoms. Will it be a dead short? Like a normal length of wire. Is this what it could be doing here for me now?
     

    Attached Files:

    Last edited: Jan 27, 2014
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Yes, quite possibly.

    The way you connected it up across the power supply (shown in an earlier circuit) put it in a situation that could have very quickly destroyed it.

    If it appears as a short circuit either way around, it's dead. If only 1 way around then you may have simply identified the leads incorrectly.

    What's that power supply you're using (voltage?)?
     
  13. apples

    apples

    97
    2
    Jul 1, 2012
    2.94v dc

    Also I just edited my above post as I worded it wrong. I had emitter and base mixed up.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Lucky that as a moderator I can see your old post as well as the new one or I'd be totally confused. It's really bad practice to do that.

    You need to determine which leads of the phototransistor are emitter base and collector. Failure to do that means you'll be getting weird and hard to interpret results. Luckily your power supply is a low enough voltage that you shouldn't do too much harm if you connect things up incorrectly (assuming you don't short battery through the transistor).

    Do you have a multimeter? You first need to determine which lead is the base, then determine which of the others are emitter and collector.

    If you can get a close up photo that is clear enough, we *might* be able to help you if we can read the markings on the device (alternatively, can you read any markings on it?)
     
  15. apples

    apples

    97
    2
    Jul 1, 2012
    The only marking on the back is a B9 it is molded in the plastic.

    I have a photo of the motor that it goes on though, that has a long number. I have in the past tried to search for that number but had no luck.
     

    Attached Files:

  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Do you have a multimeter?
     
  17. apples

    apples

    97
    2
    Jul 1, 2012
    yes and a scope
    have to tell me what to do though :)
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    OK, Does your multimeter have a diode check range?

    If so, do the following:

    Your device has three leads, black, white, and green. Your meter has two leads, red and black. You need to see what the diode check function reads for every combination So fill in this table:

    mm-red to white, mm-black to black:
    mm-red to black, mm-black to white:
    mm-red to white, mm-black to green:
    mm-red to green, mm-black to white:
    mm-red to black, mm-black to green:
    mm-red to green, mm-black to black:

    You are likely to get readings like OL for some and other readings between 0.5 and 0.8. The actual numbers are reasonably important.
     
  19. apples

    apples

    97
    2
    Jul 1, 2012
    mm-red to white, mm-black to black: .OL
    mm-red to black, mm-black to white: .OL
    mm-red to white, mm-black to green: .OL
    mm-red to green, mm-black to white: 0.571v
    mm-red to black, mm-black to green: .OL
    mm-red to green, mm-black to black: 0.567v


    0.982v on the IR LED

    So what does this tell us? I did a quick google search, is this the forward voltage drop?
     
  20. shumifan50

    shumifan50

    576
    57
    Jan 16, 2014
    As a matter of interest :
    Have you looked at bitsbox.co.uk in category optoelectronics.?

    There are 2 IR transmitter LEDS (TSAL5400, TSAL6400) 940nm for less than 40 pence each.
    There are 5 integrated receivers (TSOPxxxx) for 60p(3.3V version) to £1.33.

    To some extent these are an overkill as these devices do filtering of ambient IR by being set for a specific frequency pulsing. If the pulse is detected/broken they switch their output on/off.
    The datasheets on the site, give suggested application circuits,making life a lot easier than trying to work with parts that you cannot identify.
    If you want a simple photo sensor(rather than a clever IC receiver), you can also getthose on the same page.

    Opto devices at bitsbox.co.uk
     
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