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Finding the right sensor — Parallax Forums

Finding the right sensor

cedtinsicedtinsi Posts: 45
edited 2011-02-26 12:36 in Accessories
Welcome and Thank You for considering my Title.

I am in the process of designing an electronic device that aims to counting the number of beats of someone's heart.
I will be using a BS2 microcontroller.
My plan is to find a sensor, compatible with the Parallax Basic Stamp microcontroller, that can sense very slight changes in pressure/vibrations; I also want to be able to calibrate it so that I can set it to respond only within certain peaks of pressure/vibrations.
I know that finding the right sensor for my project is paramount to making it work.
I want the sensor to be able to capt vabrations changes by direct contact with the skin---as it will be placed in contact with the leftmost side of the chest ( unless your heart is situated on the right side!!! )
.
I browsed through the sensors available on the site, but I am perplex about the vibration sensors available; cost effectiveness is a goal of mine as well.
Knowing that your suggestions matter, great already is my thankfullness to you; for I know you will provide me with some help.

Thanks.

Comments

  • LeonLeon Posts: 7,620
    edited 2011-02-24 13:22
    Piezoelectric film sensors are sometimes used for that purpose. They are made by Measurement Specialties.
  • cedtinsicedtinsi Posts: 45
    edited 2011-02-24 14:01
    Sir, I have an issue with that sensor.
    How do I make it send a voltage to the I/O pin of the Basic Stamp only when the heart is contracting?
    when the heart is relaxing, there will still be some vibrations sensed by the piezo; I do not want it to send a voltage signal when the heart is relaxing.
    how do I make it respond only during contraction?
  • LeonLeon Posts: 7,620
    edited 2011-02-24 14:03
    You need to do some analogue processing of the signal.
  • cedtinsicedtinsi Posts: 45
    edited 2011-02-24 15:27
    Can the Basic Stamp sense the varying input voltages from the piezo and represent it as analog values on the debug terminal ?
  • LeonLeon Posts: 7,620
    edited 2011-02-24 15:33
    No. You need an external ADC. You will probably need something with a lot more performance than a Basic Stamp.
  • bee_manbee_man Posts: 109
    edited 2011-02-24 21:57
    You just want to use a microphone and count the very loud sounds made by the valves closing. You will pick up 2 sounds for every beat. I think it will be difficult to sence vibration especially with the movement of the chest wall with respiration and other muscle movements. After all a microphone is just a vibration sensor.
  • cedtinsicedtinsi Posts: 45
    edited 2011-02-26 12:36
    Mr. Leon, Mr. Bee_man,
    Thank you for your sharing of knowledge.
    Thanks to any other who contributes abundantly to making this forum what it is.
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