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I made an IR Proximity sensor but when I connect it to the battery the buzzer starts even if I have not brought anything close to the photodiode and IR LEDs. Why is it happening? I checked my connections but there should be something wrong.

Its my first project so the soldering is not very neat.enter image description hereenter image description hereenter image description here

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    \$\begingroup\$ Please post a circuit schematic. Also just a side note, that's not a PCB. \$\endgroup\$
    – jramsay42
    Commented Feb 26, 2018 at 4:34
  • \$\begingroup\$ Yes right I should have written zero PCB. \$\endgroup\$
    – user141242
    Commented Feb 26, 2018 at 7:33
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    \$\begingroup\$ You might want an opaque barrier between the LED and photodiode - otherwise the photodiode may see the LED directly. \$\endgroup\$ Commented Feb 26, 2018 at 7:41
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    \$\begingroup\$ And turn the lights down in the room. \$\endgroup\$
    – Andy aka
    Commented Feb 26, 2018 at 8:56

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There can be several issues. As the comments said you can try to shut all IR sources like environmental sources down. Another point is the potentiometer. As you wrote you did check the wiring and also the pinning. I would expect the potentiometer to be there to change the voltage on the - input of the opamp. Try to find the point where the voltage at the negative and positive input of the opamp is equal.

As I see in the circut the potentiometer is a voltage divider. When you turn the wheel you will be able to measure different voltages at the - input. I guess that the diode will be conductiv a little or that the potentiometer position (wiper position) has to be changed. So my advice is to turn (slowly) the potentiometer and se if you can find the point. Or if you have a multimeter measure + voltage ( between + of opamp and ground) and try to select the wiper position that - voltage (between - of opamp and ground) is equal + voltage.

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  • \$\begingroup\$ I couldn't find the point. The buzzer won't stop. \$\endgroup\$
    – user141242
    Commented Feb 26, 2018 at 11:52
  • \$\begingroup\$ @user141242 Can you measure the voltage at 2 and 3 in your cicuit? \$\endgroup\$
    – NeverToLow
    Commented Feb 26, 2018 at 12:51
  • \$\begingroup\$ @user141242 Actually the range of 2 pls \$\endgroup\$
    – NeverToLow
    Commented Feb 26, 2018 at 13:02
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    \$\begingroup\$ Please doublecheck the direction .of output diode (you can disconnect one lead of it and see if anything changes). I would also double check the wiring of the opamp. Check if the pins are right. Consider where pin one is when turning the board. I can't realy see were which wire goes on the picture. Does also the LED at output is on? \$\endgroup\$
    – NeverToLow
    Commented Feb 26, 2018 at 21:57
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    \$\begingroup\$ You could cover the photodiode with a sheet or something. It could be the diode. I mean if you have a second one you could change. With a multimeter or voltmeter you could measure the voltage at + and - of the opamp. That would give you an idea where the problem is. \$\endgroup\$
    – NeverToLow
    Commented Feb 27, 2018 at 8:39

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