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Coin counter photo-detector

Discussion in 'General Electronics Discussion' started by PWood, Jun 22, 2012.

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  1. PWood

    PWood

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    Jun 22, 2012
    Hello, All! This is my first post and my first time on this forum, so I'll get right to it:

    I am looking to find out as much as I can about an electronic component that is photosensitive to infrared LED's. I am including some pictures of two of them. This is from a coin counter. In the coin counter, when a coin passes between an LED opposite the light sensor, the coin count increases by one. Well, some of these have gone out (of which I'm sure, since switching working ones around to other stations/coin slots remedies the problem at those stations). So, I am looking to buy some of these from Digikey or someone and replace the dysfunctional ones, but I don't know where to look (that is, under what component name/type).

    Anyhow, any help would be much appreciated. I've found some things that I think work the same, but I am looking for something that appears as identical as possible (but I need the name of the type of component this is!).

    I hope that was clearer than I think it was. It's kind of late, and I've been trying to study, so this is a study break. My apologies, etc., for anything I've made unclear.

    Thanks in advance!
     

    Attached Files:

  2. Raven Luni

    Raven Luni

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    Oct 15, 2011
    Those are phototransistors. If you're replacing them be sure to get the positions as exact as possible. The circuit works by comparing the on / off times as the coin passes to work out the diameter of the coin and thus its value. Hope this helps.
     
    Last edited: Jun 22, 2012
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Hi PWood, welcome to Electronics Point and thanks for explaining your question so clearly.
    As Raven Luni says, they're probably photo-transistors (or perhaps photodiodes). Can you lift one up to see if there's a part number printed on the back?

    You can look on Digi-Key: http://www.digikey.com/product-sear...ical-photo-detectors-phototransistors/1967049
    They have a pretty wide selection, and you can use the filter table to narrow it down. In "Mounting Type" Ctrl-click on the "Through-hole" options. In "Orientation" select "side view". In "Package/Case" select "radial - 3 leads", "radial, side view", and "side view", then click "Apply Filters".
    You'll have to look through the pages to find a physical match, using the photos on the left side.
    There are quite a few characteristics that have to match reasonably well for a replacement to work. The wavelength should match the light emitted by the LEDs, and the viewing angle is probably important for this application too.
    It would be best if you can get an actual part number from an original part.
     
  4. PWood

    PWood

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    Jun 22, 2012
    Raven- thanks for your response and for the tip; I'll try to position it as close to the original as I can.

    Kris- thanks for your response and for directing me toward the replacement parts. I will try to determine the part number from the originals. I know the exact LED part number that went with the part, so I suppose pairing the photo-transistor by those specifications could be an alternative, if I can't find the original part number. What does radial mean, in regards to the photo-transistor?

    On a side note, the reason I am trying to replace these (besides liking to mess with circuits in the ways a novice can) is because 1) replacing a nice coin counter like this is really expensive, and 2) the parts are no longer supported by the original company. I have looked at what resellers can do for me, and they want US$140 (no decimal there!) to replace the chip and its counterpart. I figure these parts might cost $5 for me to assemble, so the reseller's price seems a bit much for me.

    Sometime this weekend I'll try to determine the original part number. I'll post anything I find.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Knowing the LED part number will tell you the wavelength you should aim for, but there are several other characteristics of the phototransistor/photodiode that need to be right as well.
    Radial and axial refer to whether the leads come out the same side/end of the device (radial) or whether they come out opposite ends (axial).
    It would really help if you can find a part number on an original device. Even just a manufacturer's logo would help.
    If you can't, you can still use a bit of trial and error. You could start by tracing out the circuit diagram of that small board with the devices on it, and if possible, the circuitry at the other end of the cable that connects to it. It could also be helpful if you can measure voltages on a working board. But let's hope you can come up with a part number.
     
  6. PWood

    PWood

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    Jun 22, 2012
    OK, so I pried one away from the PCB, but there wasn't any sort of identification whatsoever. It looked like the front without the little globule. Are there any suppliers that might carry some different products from Digikey? I couldn't quite find a match. I'll try to get a voltage reading today.
     
  7. PWood

    PWood

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    Jun 22, 2012
    For the above post, I meant I'll try to get a voltage reading on one of the functioning ones today. I just wanted to clarify that.
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You could try Element14, Mouser, Fry’s Electronics, RS Components, and maybe Jameco if they still exist?
    I would like to know whether all three pins on the devices are used, or just two. It would be useful to have a circuit diagram of that board. Are there any other components? Perhaps surface-mounted resistors under the board? If not, then probably only two pins are used on each device. The connector has only three pins, right? Presumably one is common (probably ground) and the other two are the signals from the two devices. You could start with a continuity check from the ground of the main board to the connector, and from there to the pins of the devices, and a continuity check from the other device pins to the connector. This will at least tell us which pin does what.
    When you do the voltage measurements, you'll need to be able to simulate a coin interrupting the path, so we can see voltages with and without illumination.
     
  9. Raven Luni

    Raven Luni

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    Oct 15, 2011
    Looks like a 4 pin connector to me. I'd say those are Vcc, Gnd, and the outputs of the 2 transistors. Cam you take a pic of the other side?
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Raven, I think you're right. In that case the detectors are more likely to be active devices like the OPL550/551 http://www.optekinc.com/datasheets/OPL550.PDF since there don't seem to be any pullup resistors on the board so there is no need for a supply rail on the board if the devices are just photodiodes or phototransistors.
    But those devices aren't exact matches for the Optek parts - the internal arrangement of the metal bits, and the pins, are clearly different.
     
  11. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    Looking closely at the second pic and where the copper shows through it looks like there are definitely surface mount components on the other side
     
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