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Proximity sensor

Discussion in 'General Electronics Discussion' started by tnnelectro, Jun 18, 2020.

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  1. tnnelectro

    tnnelectro

    45
    0
    Apr 5, 2012
    Hi,

    I made a proximity sensor with this IR emitter LL-503IRC2V-2AD and this phototransistor LTR-3208E
    wavelength 940nm.

    it works well, except if I expose it to sunlight both directly and indirectly ...

    can you recommend something to solve?

    can I put a filter in front of the window where the emitter and the phototransistor are located?

    it is urgent thanks….
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Sunlight contains IR. An optical filter cannot block IR because that makes the whole purpose moot. So IR from sunlight will interfere with you sensor.
    You can, however, use modulated IR. E.g. use a 555 to pulse the transmitting LED at a few kHz. Then add a high-pass filter to the receiver. As sunlight will create a DC component, this will be blocked by the high pass.
     
    hevans1944 likes this.
  3. tnnelectro

    tnnelectro

    45
    0
    Apr 5, 2012
    ok this is the schematic of my circuit ... is it possible to modify this?

    SENS.jpg
     
    Last edited by a moderator: Jun 18, 2020
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Possible: yes.
    Quick and easy: maybe.

    The transmitter part is simple: add a 555 as astable mutivibrator to drive the LED. You'll find suitable circuits on the internet en masse. Use 1 kHz or higher to exclude 50 Hz or 60 Hz hum from disturbing the circuit.
    For the receiver you can try this:
    - remove C9, U2, R7, V2, C4
    - connect the collector of PH1 to the left side of C5 (where U2, pin 2 used to be connected).

    Only the AC signal from the LED will pass through C5 and trigger U1. Give it a try.
    To reduce sensitivity to low frequency (50 Hz or 60 Hz) interference you may reduce C5 from 100 nF to 10 nF or even 1 nF. It's up to your experiments.
    If the circuit does not operate reliably and stable, a signal conditioning amplifier between PH1 and C5 may be required.
     
  5. bertus

    bertus Moderator

    683
    237
    Nov 8, 2019
    Hello,

    Or you could shield the sensor from the sunlight as AlbertHall told you on AAC:
    Alternatively, you could put a small tube in front of the receiver so it can only see directly in front.

    Bertus
     
  6. tnnelectro

    tnnelectro

    45
    0
    Apr 5, 2012
    I'm sorry is this okay to power the 1khz emitter?

    I have a 53% dutycicle okay anyway?

    ne555 astabile 1khz.jpg

    can you tell me the filter?
     
  7. tnnelectro

    tnnelectro

    45
    0
    Apr 5, 2012
    so can it fit?
    I have a doubt about the filter on the receiver out ...

    SENS_new.jpg
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Yes. Connect the LED with series resistor to pin 3 of the 555.
    So do I. This is what I tried to describe:
    upload_2020-6-18_18-22-55.png
     
  9. tnnelectro

    tnnelectro

    45
    0
    Apr 5, 2012
    I did ... it doesn't work
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    What means "it doesn't work"?
    What do you expect it to do, what does it do instead?
    Do you have access to an oscilloscope for looking at waveforms?
     
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