Viewing 3 posts - 17 through 19 (of 19 total)
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  • #3938
    Avatartheremino
    Keymaster

    The last chart that I presented must give values ​​that grow when the turbidity rises.
    But have you noticed that in the last pattern I specified that the sensor is put back in its original state?
    You have restored the unit as it was originally, ie with the photo-transistor to the 3.3 It was positivo?

    And maybe tell me how you changed the pattern, and why?

    #3946
    AvatarLuciano
    Participant

    The sensor’ as out of the factory and the scheme used and’ improved and simplified version, the only difference’ I fed all with the stabilizer to 5V.

    I send the scheme with my changes, as you can see I added a 2.2K resistor sensor output, and trmmer zero and’ adjusted all set. I did this because if regolavo zero to a few hundred mV (They started from the adjustment from 200mV to 1V.) with gain at most had a variation between 0 and very low in the order of 1000NTU 40/80 mV

    For the calibration of 1000 NTU I used my “solution” and adjusted the gain for 3100 mV card's output, for 0 NTU I used distilled water, exit of I board 2348 mVchange settingmodification

    #3949
    Avatartheremino
    Keymaster

    Use the 5 volts does not cause problems.
    The resistor 2.2 k can not only reduce the sensitivity, not increase.
    Hold R1 to the maximum no good (It may be changed with 10K or more).
    To have 2 O 3 volt output to no good, you have to start at about 100 millivolt con 0 NTU and this voltage must rise as the turbidity increases.
    If you can not adjust to 100 mV 0 NTU then it means that the transistor receives little light. (The LED is pointed right? The photo-transistor works well and has the collector and emitter not reversed?)
    If you can not adjust to 100 mV 0 NTU, then you could increase the value of the trimmer zero to 10K or even 47K.
    With 2 O 3 volt outlet you work the 358 close to saturation and then works in strange and perhaps this is why you have the inverted signal.

    The scheme is right and the output voltage must increase when the turbidity increases
    – By increasing the turbidity of the phototransistor receives less light
    – So the phototransistor passes less current
    – So the voltage of the negative input 358 It tends to fall
    – Then the voltage on the output tends to rise

    For me you should:
    Delete the resistor 2.2 K.
    Adjust R1 for 100 mV with approximately 0 NTU .
    If the gain is not enough maybe you will increase R4 to 100k, or even 1 mega .
    More raise R4 and the greater the gain, but will also become more difficult to adjust R1 (which must always be adjusted to 0 BTU = 100mV).

    If you can not make it work
    Write to me at “engineering spiral Theremino dot com”, so we'll talk by phone or Skype and we will put in place.

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