Infrared Beam Break Receiver

Discussion in 'The Projects Forum' started by spike1947, Apr 10, 2016.

  1. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi

    Can anyone help me with the attached schematic , I don't really understand were the line of " VREF" connects to , maybe I can not see the tree's for the forest ! .

    cheers

    spike
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi spike.
    Look at IC1D OPA output.
    Eric
     
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  3. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi

    Thanks for your reply , I can see in IC1D that 13 and 14 on the IC are fed to 14 ,but were does the output of 14 go to ! ,I still don't understand " VREF " , also is the output of IC1B supposed to be to output 7 , and were doe's COMP go to .

    Please excuse me I am just getting into Electronics , maybe I should read a bit ( lot ) more ! .

    spike
     
  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    This circuit is an AC-coupled system processing the signal from a phototransistor, but it's operating off a single positive supply. IC1D is a buffer amplifier which generates a pseudo-ground at about 40% of the input power supply level. This is then fed to the + terminals of IC1A and IC1B, which allows them to operate both above and below the "reference voltage".
     
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  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Also the light emitter must be modulated.
    A constant light source will not work.

    Bertus
     
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  6. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi again
    Do I take it that 14 , 3 and 5 of the IC LM324 are linked together ! , still don't know were COMP goes to .
    Hi
    Thanks for that info , got that , the circuit is fed from a 9 Volt battery ! , could you tell me also were do the COMP connections go to .

    spike
     
  7. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi spike
    COMP goes to D3 driven by the IC1B OPA.
    E
    NOTE: what Bertus has posted, ref modulated source

    EDIT:
    Consider the 'pointed' end of a OPA schematic symbol as an Output
     
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  8. John P

    AAC Fanatic!

    Oct 14, 2008
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    IC1B is a sort-of peak detector which attempts to charge C3 via D3, while the voltage divider formed by R7 and R8 tends to hold a constant voltage there. If the voltage on C3 (the designer calls it COMP) exceeds another reference voltage generated by R9/R10/R11, then the output of IC1C goes high and turns on T2, which sounds a buzzer and lights an LED.

    I'd have wanted to add a little one-shot timer which could give a minimum flash/buzz period when the output trips, because it seems to me as if this circuit could give you tiny little signals which would be difficult to detect. Maybe a few more components around IC1C could make the timing function happen.

    Edited to say sorry, I had that backward. The output on COMP is normally high, and goes to the negative input of IC1C. Of course as an intrusion detector, the normal state of the system is with the light beam unbroken! You want the output to trigger when there's no light hitting the sensor.
     
    Last edited: Apr 10, 2016
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  9. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi

    OK guys , I think I have got it now,
    Hi
    Thanks for your reply am attaching a schematic of the Transmitor
    except IC1B should that output be marked 7 to D3 !
     
  10. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi

    Thanks for your reply , yes it is only a very short burst to the alarm , I will have to see how I can increase the time ,any idea's ! .

    cheers

    spike
     
  11. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi

    Thank you all , for all your replies , I have tried to do a schematic that I can understand from the schematic I first put on here , would anyone be able to have the time and patience to check it out ! .

    cheers and again thanks , what a great site , and nice people willing to help people like me that are very new to electronics .

    spike
     
  12. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi spike,
    Looks OK to me, C3 is 2.2uF , will take a second look over.

    E
    EDIT:
    I agree with post #13
     
    Last edited: Apr 11, 2016
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  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    D3 needs to go to the right of D2 in the lower left quadrant of your 324 chip.
     
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  14. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Thanks again Guys for your patience and help , is the attached schematic ok ! .
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    History proves you wrong.

    But pulsed works a lot better - a filter at the receiver that only passes the pulse frequency, coincidentally also excludes interference from mains lighting.
     
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  16. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    @ian field , The receiver schematic has no filtering.
    There is an amplifier and a full wave rectifier.
    The only filtering may be the coupling capacitors:

    IR_receiver_MK120.jpg

    Bertus
     
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  17. ian field

    Distinguished Member

    Oct 27, 2012
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    What do you want me to do about it?!

    There's designs available on the web - the TS can select one based on the advice given here.

    The original break beams used a bulb as the light source - too slow for pulsed.

    High speed semiconductors made pulsed operation possible since the invention of LEDs.
     
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  18. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    A DC coupled detector/amplifier is susceptible to the ambient lighting conditions.

    Unless he uses a decent collimator tube at the detector, the detector, in bright light will biased in the On state and become useless.
    Also if the ambient light level is high there will be sufficient light to keep the detector signal in the 'unbroken' beam condition.

    The web is littered with Threads from newbies saying that their DC coupled beam breaks are not working as expected.

    You can get around the ambient light problem by using a 'slicer' circuit at the detector end, but it's easier to switch the emitter and use a AC coupled detector system.

    E
     
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  19. spike1947

    Thread Starter Member

    Feb 4, 2016
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    Hi Guys
    I am only wanting it to be off any use during the night time really .

    cheers

    spike
     
  20. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The receiver has two 3.4 kHz single pole highpass filters in series.

    Update: What is the frequency of the transmitter?

    ak
     
    Last edited: Apr 13, 2016
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