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Need help with human pulse detection circuit

Discussion in 'General Electronics Discussion' started by ZanShini, Mar 20, 2018.

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  1. ZanShini

    ZanShini

    7
    0
    Mar 2, 2018
    I referred to this article (https://makezine.com/projects/ir-pulse-sensor/) for making one. The article has the schematic diagram but here (https://imgur.com/QnIRwcz) it is for convenience if you don't want to go through the article. I wanted to use a 2 digit counter with 7 segment displays instead of Arduino. Counter schematic 1 (https://imgur.com/AKQEcsJ) & Counter schematic 2 (https://imgur.com/OVRGwHQ)
    Initially no pulse was recorded by the counter and the count was static.
    The modifications I've done to the circuit(after reading the comment section of the article) are as follows:
    1. I've connected the photodiode in reverse bias and replaced the 39K resistor with a 10K one.
    2. I was still not getting any output pulses after modification 1 so I've taken the output directly from the LM324 instead of amplifying it by the transistor.
    After these modifications the counter is receiving some pulses but the count is erratic(skipping randomly) and it is counting even without placing the finger on the emitter-sensor setup. I've captured the output by an oscilloscope. Most of the time it is random noise signal with distinct spikes when the finger is just brought over or removed from the IR LED and photodiode(which indicates it is working fine as a proximity sensor as it's supposed to do) but I was able to capture clean pulses once or twice. Here is how the clean pulses look like(During such clean pulses I've verified the my pulse rate by manual counting and the results matched). Please don't think the output is always like that. Most of the time it is like this (https://imgur.com/HXmIx9Y) or far worse. But irrespective of whether I get clean pulses or not the counter readings are always erratic.
    I need your suggestion on what is going wrong with the circuit & also on any changes that can be made to the circuit for desired operation. It would also be great if you're able to provide an altogether different circuit or article(like transmissive detection instead of reflective detection etc.) by which human pulse can be detected and the output is readable by a counter circuit.
    Here (https://imgur.com/EQahDPr) is also how my circuit physically looks like. It shows nothing save the fact that the IR LED and Photodiode are not fixed and free to move to certain degree(which may be the cause of noise output but I'm not sure).
     
  2. Hopup

    Hopup

    253
    36
    Jul 5, 2015
    Check the connections, solderless board is not exactly best way to make circuits.
     
  3. ZanShini

    ZanShini

    7
    0
    Mar 2, 2018
    Thanks for your response. But doesn't the output suggest that at least the connection is okay?
     
  4. Hopup

    Hopup

    253
    36
    Jul 5, 2015
    It worked for a while, so it could be bad connection between some component or wire. Maybe try wiggling the wires or components to see if it varies the output.
     
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