IR detector signal input to the PC via SoundCard (mic port)

Discussion in 'The Projects Forum' started by MrOmnos, Jun 6, 2014.

  1. MrOmnos

    Thread Starter New Member

    Jun 6, 2014
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    So...I am working on this ir heart rate monitor project...found it on the internet!! Its a really simple circuit...an ir emitter and a detector pair is used as a sensor...which is touched to your skin...it shines light up your skin and then reflected light is detected by the detector..this signal is then fed into an lm386 which amplifies the signal which is fed into an analog pin of an arduino or any micro controller...There's a code running on this microcontroller which sends this data via serial communication to the pc..there's a processing app on pc which reads this data and visualizes it (well it actually draws a straight line on the screen :p if you know what I mean) so..I was thinking if I could send that signal though my microphone port on my pc...then write a app that would visualize it!! I mean..what my lm386 generates is just a signal right?? (I know Lm386 is not ideal for such projects...it's noisy...I had Lm386 laying around so i used it..the signal was really noisy but then i blasted that amp with caps..now its presentable..i will replace it!! ) Similar to what my mic generates...if it is possible..it would fun :D ...i mean i could plug that into my android devices and write and app for it!! I know that my soundcard won't respond to such low frequency signal!! How do i convert that signal to something that my soundcard will detect??
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That depends what you want from your heart beat signal. If it is purely the rate for example, with no interest in the heart beat strength/waveform, then you could use the IR Rx signal (after amplification if necessary) to gate an audio oscillator on/off.
     
  3. MrOmnos

    Thread Starter New Member

    Jun 6, 2014
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    I want to preserve the waveform!! Someone on another forum suggested me to use a VCO (74HC4046) will that preserve the wave form?? And if only rate was needed...how should be the app written?? Never worked with audio oscillator
     
    Last edited: Jun 6, 2014
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You will get an audio tone whose frequency (pitch) varies according to the envelope of the IR Rx signal. The app would then have to analyse the frequency and re-convert it to the required envelope.
    For measuring rate only you could detect fixed points in the Rx signal, e.g. signal peaks, and use those to switch an audio oscillator on/off briefly. The interval between the resulting sound bursts would have to be detected by your app to determine heart rate.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The sound card input is capacitive coupled and may not pass very low frequencies like a heartbeat.

    Instead of a VCO you could amplitude modulate a carrier? That will be recordable by the sound card. Maybe that is what someone called a "VCO"?
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    A VCO running at ~1kHz or so should be fine.
     
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