Heart Rate Frequency to Voltage

Discussion in 'The Projects Forum' started by TJBocch813, Mar 28, 2011.

  1. TJBocch813

    Thread Starter New Member

    Mar 28, 2011
    6
    0
    Hi All,

    I am working on a design project that involves an optical heart rate sensor that extracts a pulse through the fingertip. The IR LED/phototransistor sensor is working well and outputting a clear signal (getting an LED to blink on an off), but now I want to send this to a frequency to voltage converter and eventually to a dot/bar driver to output the HR on a set of LED's.

    The problem is that I do not think that any F-V IC's (e.g. LM2907) can pick up a frequency that small (~0.5-4 Hz) without severe repercussions with response time or ripple if they can even output a signal at all.

    Any help or ideas for this would be great.

    Thanks!
    -Tom
     
  2. russpatterson

    Member

    Feb 1, 2010
    351
    16
    Do you just want to see the BPM number on an alpha-numeric LED's or just show the BPM as a scale on a set of LED's (like a volume meter)? Why do you have to convert to frequency?
     
  3. TJBocch813

    Thread Starter New Member

    Mar 28, 2011
    6
    0
    I just want the BPM to show up on a 10 LED scale (each led will represent 20 BPM, with the last one representing 180-200 BPM). It will basically be a heart rate VU-meter. I currently have a digital signal coming from the circuit, but having a frequency to voltage converter would help me display it linearly on the LED system. Is there a different way to achieve that?
     
  4. russpatterson

    Member

    Feb 1, 2010
    351
    16
    I'm sure there is but taking your digital signal and then deciding which LED's to turn on via a micro controller sounds a lot easier. How many separate LED's do you want to control? How about using a (or some) shift registers to set which LED's turn on?
     
  5. TJBocch813

    Thread Starter New Member

    Mar 28, 2011
    6
    0
    I was planning on using an LM3914 IC, which controls 10 LED's separated by variable reference voltages. I knew I may have been biting off a bit more than I could chew without going to a micro controller.

    Really, all I need to display is 5-6 LED's representing about 100-200 BPM, and I'm willing to go to a microcontroller if needed.

    How would you incorporate shift registers?
     
  6. russpatterson

    Member

    Feb 1, 2010
    351
    16
    If you're looking for simple. Just buy an Arduino and hook the LED's to output pins and turn them on/off that way. Shift registers let you push a big string of 1's and 0's out to them, then they drive pins high or low based on having a 1 or 0 in a given spot. The cool thing is that you can daisy chain them so that you can control hundreds of pins and only use 3 pins on your MCU.
     
  7. TJBocch813

    Thread Starter New Member

    Mar 28, 2011
    6
    0
    Sounds pretty interesting. Let me do some research and I'll get back. Thanks a lot for your help.
     
  8. CVMichael

    Senior Member

    Aug 3, 2007
    416
    17
  9. TJBocch813

    Thread Starter New Member

    Mar 28, 2011
    6
    0
    CVMichael, that is actually the article that helped the me build the first part of my circuit, but where he was going into a microcontroller, I was going to use a FV converter, which I am now realizing (given being a relative novice in electronics), that will probably be extremely difficult for me right now.

    On the flip side, I have next to no experience with microcontrollers (!!), as I've been working with mostly analog circuitry (I know, get with the times) and I actually think that this would be a good time to start.

    I'm assuming my best bet will be to start on the Arduino Uno board?
     
  10. russpatterson

    Member

    Feb 1, 2010
    351
    16
    TJBocch813 likes this.
  11. TJBocch813

    Thread Starter New Member

    Mar 28, 2011
    6
    0
    Thanks, Russ! Arduino should be here tomorrow so I can start messing around. The paper helps a lot too. You are the man!
     
Loading...