How do Heart Rate Grip Sensors on Exercise Bikes Work?

Discussion in 'General Electronics Chat' started by Zero Potential, Dec 6, 2015.

  1. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    I have a Nautilus NR3000 recumbent exercise bike I bought in 2006. It has grip sensors which are supposed to measure my heart rate. If the machine can measure your heart rate, it can display it for you and use it to alter your exercise routine, which is nice.

    The sensors have never worked correctly. I know the product is to blame, because the sensors on commercial-grade bikes work just fine. Nautilus has been no help.

    Each sensor has two metal panels that form part of a hand grip. You're supposed to hold each grip so your palm touches one panel and your fingers touch the other.

    I am thinking it might be possible to fix this thing myself, but I don't know how the sensors work. I'm wondering if anyone here has a general idea of how this sort of gadgetry works, so I might have some clue what's going wrong.

    Before anyone asks, the problem isn't that my hands are dry.

    Thanks for any help you can provide.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
    619
    Google "how do hand grip heart rate monitors work" (this is what Google suggested when I started typing).

    This was the first hit.

    From the first paragraph:
    The Hand-Grip Heart Rate Monitor measures a person’s heart rate by registering the small electrical signals carried across the surface of a person’s skin each time his or her heart contracts. This signal is measured at the surface of the skin by electrodes embedded in the hand grips of the Hand-Grip Heart Rate Monitor.
     
  3. Zero Potential

    Thread Starter Member

    Mar 25, 2015
    64
    2
    Thanks for pointing out the existence of Google, and for underlining "first," but this is not actually what I was looking for. I should have been clearer.

    I am aware of the existence of Google, and I have been using it for an hour or so without useful results. I am also aware that heart rate monitors detect electrical signals, so it is not necessary to discount alternative theories involving telekinesis or pixies.

    What I am actually looking for is information regarding the type of components that are likely to be used in such sensors and what I might want to look for when trying to diagnose the problem that causes a lack of sensitivity.
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    If your heart rate monitor is lacking sensitivity then you must have worn off the ogre sweat from the hand grips. See the ogre under the bridge for replacement sweat. But if your exercise machine was built in this century, try googling (spelled G O O G L E), "differential amplifier".
     
    Last edited: Dec 6, 2015
  5. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,884
    1,005
    Try wetting your hands before using and see it that helps.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,120
    3,046
    This might get you started. Also, look up the circuit used in those ubiquitous chest straps. I've seen it somewhere. I think the handlebar versions use a similar method of detecting the heart beat.
     
  7. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    In general debugging, I try to isolate the problem to a specific component. So my first test would be to get a few other people to try it, and see if it works for them. If it does, it might just be that you have dry skin, and could try moistening your hands, or if you can get hold of some electrode gel that they use for ekg tests, even better. If the circuit works for no one, I'd start by tracing where those contacts go, and looking for either a short or open. If it works but is flaky, I'd look for a high-impedance short, and wash the area with alcohol (then dry it thoroughly). I had a similar problem at work, a circuit that was supposed to draw just about 1 uA drawing 10 or more uA, a problem at the time under battery power. Turned out to be salts on the board and condensation. Something that will measure your heart rate is working with a very small signal, so I think that sort of thing would be important. It's possible, but I think less likely, that the problem is actually on their board.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,120
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    Could even be as simple as a poor connection of the sensor jumper to the circuit board.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,043
    3,806
    Ok.
    you could have saved yourself a bunch of frustration by just buying a fitbit
     
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