Photosensors inside old mouse...

Discussion in 'General Electronics Chat' started by Marc0, Sep 4, 2012.

  1. Marc0

    Thread Starter Member

    Nov 28, 2011
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    I have a couple of old opto-mechanical mice. Each of them has two photo sensors placed in front of two ir diodes. They have three pins, but can't figure out how those sensors work, where can I found some infos?
     
  2. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    Go to a vendor website and pretend you want to buy an IR photo-transistor or photo-diode. Then download datasheets until you find a 3 legged device.
     
  3. Markd77

    Senior Member

    Sep 7, 2009
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    If I remember right, there are two sensors in each package. The centre pin is common to both sensors.
     
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  4. absf

    Senior Member

    Dec 29, 2010
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    I agree with Markd77. The older design used 4 pairs of photo sensors and IR LED. They must have combined 2 sensors into one. See pictures attached.

    Allen
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    They are a 3-leg opto interruptor sensor, one leg is ground, one is the LED (normally about 1.3v if you measure on your multimeter's "diode test") and the other leg is the output of the phototransistor sensor.

    As a good test you can use a 1k resistor from 5v to the LED leg, a 47k resistor from 5v to the output leg, connect the ground leg, and then the output leg will go from about <1v to >4v as you break the beam.
     
  6. Marc0

    Thread Starter Member

    Nov 28, 2011
    42
    1
    To figure out how those pins are sorted I have to take a close look to the pcb's... Do you happen to know what voltages/amps do supply an rs232 port to a mouse?
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yep, they run about 8v or 9v supplied from the DTR and RTS pins of the RS232 port, usually through a couple of glass diodes into the main cap which will be the largest electro cap about 47uF to 220uF range. That cap is a good place to apply power, but apply power through a resistor as those old mice are often crudely regulated using a 5v zener diode. The whole mouse will only need 10 to 15mA or so.

    You shouldn't be scared of those sensors they are very simple and you don't really need to run the whole mouse. If you have the PCB try to see which is the ground pin, it will connect to the ground plane or a large track that connects to lots of stuff including the main electro cap - pin. The LED pins will have a series resistor of a lowish value probably 470 ohm to 1.5k range.

    Like I said above, once you know the ground pin of the sensor you just need a 5v supply and the two resistors, and a voltmeter. The sensor LED will only use about 3 or 4mA.
     
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  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Time ago I opened one of those and managed to identify all pins by connecting the mouse to the port in a PC where it was used.

    Be patient and draw the whole circuit. Just measuring voltages you should identify all pins.
     
    Last edited: Sep 9, 2012
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