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Reverse engineering of temperature sensor

Discussion in 'Sensors and Actuators' started by Gianluca, May 19, 2018.

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  1. Gianluca

    Gianluca

    2
    0
    May 19, 2018
    Hello everybody,
    I do have a temperature sensor that i am trying to integrate in a project. The device was supposed to be an infrared temperature sensor, but when i opened it up to try to understand how to get a useful signal out of it I only found a small PCB with a LASER diode (TOSHIBA TOLD 9200) pointing at the lens. I understand that the laser beam is used as an aid in aiming the sensor at the correct spot for temperature reading, and since there are no other components pointing at the lens, I can only guess that the tiny signal from the photodiode inside the laser diode is used to get a reading (obviously after turning the laser off). this is supported by the presence of an OP AMP (AD760). I have drawn up the circuit board and I am attaching pictures of the original board and my drawings (one of them with transparent components so you can see where the tracks are going underneath them). I have ZERO experience with SMD components, I managed to understand that the black ones (marked 1002) should be resistors and the glass orange one a diode. the other components (gray ones) are they capacitors?? there are no marks on them. and the black one with three pins marked A7p what is it?? (only 2 pins of it are connected) I tried to search the net but had no luck. there are 5 wires coming out of the device: yellow, white/red, green, red, black.
    Is there anyone who can help me make sense of that? (I am ready to pay for that if needed)
    001.jpg 001.jpg solid.JPG transparent.JPG

    Kind regards
     
  2. kellys_eye

    kellys_eye

    4,276
    1,146
    Jun 25, 2010
    What does the signal feed? Is it analogue or digital?

    How does it display the data normally?
     
  3. Gianluca

    Gianluca

    2
    0
    May 19, 2018
    uh, it is supposed to be a temperature sensor. i did not had the chance of meausuring it on the original equipment, but i guess it has an analog output, because there is an op amp on it...
     
  4. kellys_eye

    kellys_eye

    4,276
    1,146
    Jun 25, 2010
    What I was getting at was how the signal is subsequently processed. You might have found (for example) that the processing circuitry delivered an RS232 (somewhere) as part of its function - many digital measuring gauges have such, as the hacking fraternity will attest to - which would be easier to work with.

    However, simply measuring the voltages at the various pins you list will reveal at least ONE pin that (should!) varies with the change of signal. Measuring that and applying a test signal from known temperature sources to achieve some sort of calibration.

    The pinout of the op-amp will reveal the power connections (seemingly the red and black wires from your diagram), the yellow wire may be the laser diode on/off signal, the green may be the amplified signal from the IR receiver diode.

    The drawing below shows the diode pinout - find the datasheet for the op-amp and you'll have as much information as you need to get where you're going (I presume)

    Laser diode.png

    It may also be the case that the laser diode (aiming) part is modulated and the 'detected' signal measured during the 'off' period.
     
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