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Complete Newbie with some simple questions.

Discussion in 'Electronic Basics' started by Bishop, Dec 5, 2004.

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  1. Bishop

    Bishop Guest

    Hi all, I'm a complete newbie here. I'm a VB programmer and could use
    recommendations on what parts I need, suggestions on part makes and models.
    As with most things, I want to keep the price as low as possible.

    What I want to do it use a heart rate sensor and a magnetic sensor to record
    heart rate and revolutions when someone is riding an exercise bike. Below
    is a brief illustration:

    Hear Rate Sensor and Magnetic Sensor >>> Not sure what stuff I need here >>>
    digital IO board >>> Windows API for the Digital IO board.

    A couple other things that play into this:
    1. The Computer with the digital IO board may be a hundred feet or so from
    the bike. I'd like to use cat5 cabling to span the distance.
    2. Eventually I'd like to record data from multiple bikes at the same time
    on the same computer. This is not necessary for the first prototype but
    it's worth mentioning for the parts list.

    That's it. I'd appreciate any ideas, thoughts, suggestions!

    Thanks, -Ken
  2. CFoley1064

    CFoley1064 Guest

    Subject: Complete Newbie with some simple questions.
    Hi, Ken. I'm assuming you want an ethernet connection between your PC and your
    I/O board. I'm also assuming you have some facility in programming ethernet
    with VB.

    You're going to need some kind of dedicated controller on the I/O board end, if
    for no other reason than to run the network connection. Also, given excercise
    bike wheel speeds, you'll probably need a counter on the I/O board, especially
    if you're thinking about more than one bike per controller.

    Having said that, I think the best low cost way to do what you want is to embed
    an ethernet-ready SBC at the I/O end, and learn the small amount of programming
    necessary to get it to do what you want.

    If I were in your shoes:

    1) I'd look at a simple circuit to measure heartbeat

    which has an open collector output.

    2) I'd use a magnet and a reed switch or hall effect switch for measuring
    wheel revolutions

    3) I would use one of the Rabbit boards with ethernet shown at

    for the I/O. Look particularly at the RCM3200 development kit. It's got legs,
    and is fast enough and has I/O enough for many bikes and heart monitors at one
    time. It does program in a proprietary C, but is inexpensive to start with.
    They're advertising a complete development kit including protoboard, all cables
    and development software for one of these ethernet enabled boards for less than
    $350 USD on their website.

    4) As a newbie, I would get the Jan Axelson book "Embedded Ethernet and
    Internet Complete: Designing and Programming Small Devices for Networking",
    available from hobbyist sources or Axelson's Lakeview Research website. Get
    this first. It costs $50 USD and is worth every penny. It uses the Rabbit for
    project development, and has lots of code on the disk that you can just cut &
    paste for the RCM3200 module.

    Once you get your project down, each individual RCM3200 module is $79 USD. You
    also might have the option of going with one of the less expensive Rabbit
    modules for production. The RCM2200, which might do what you want, is only $55
    USD each.

    I know this isn't exactly what you wanted to hear, and might be a little more
    than you originally thought you'd spend, but I think it's about the perfect mix
    of low cost and ease of learning curve for a limited quantity of units for a
    newbie, especially if you've ever done any C programming.

    Good luck
  3. I wouldn't bother thinking abour designing anything until you have
    exhausted the possibility of an off-the-shelf solution.

    There have got to be heart rate monitors with RS232 or similar outputs,
    Multiple units? - no problem, get a multi-port RS232 card. You could
    even use and RS232 wireless modem if you didn't want any cables.

    Similar thing for the speed sensor, there is probably an RS232 or
    similar solution available. Alternatively if you wanted to roll your
    own you could feed the sensor straight (after converting to TTL) into
    the parallel port and count in real-time. No I/O card needed.

    Dave :)
  4. Bishop

    Bishop Guest

    Thanks for all the recomendations! I've got some reading to do. Price is
    actually close to what I was guessing. I'll start looking through all this.
  5. Bishop

    Bishop Guest

    I actually found some serial interfaces and multiport serial. That may be a
    less expensive option. I'll hae to make sure there is enough speed for what
    I need. I'm not opposed to finding something already out there if it dosn't
    cost me more and has a windows api. I haven't found anythng yet but maybe
    I'm not searching correctly for it.
  6. Bob Masta

    Bob Masta Guest

    One thing you might want to keep in mind is that almost
    every system these days comes with a 2-channel 16-bit
    A/D converter in the form of a sound card, and there is a
    well-developed API for it. It's AC coupled, typically at a few
    Hz or so, but that's fine if you are recording raw EKG and
    using the computer to get rate. (I think the QRS complex
    that everyone triggers on for rate determination is something
    like 1 kHz equivalent.)

    Bu I expect you are using the photo-optical blood flow type
    of sensor. I haven't used these, but I am sure the pulses
    are much broader in waveform. This may not be a bad thing.
    If you can arrange to have the RPM be a fairly high frequency
    (several kHz) you can use it as a chopper to modulate the
    blood signal, then use the computer to demodulate them.
    Note that for this technique to work the chopper frequency
    has to always be at least twice as high as the highest blood
    frequency component you need, so if you are trying to track
    from zero RPM you may need an offset. This modulated
    signal should have no trouble travelling 100 feet on any
    sort of cable.

    You would be putting both signals on one wire to
    one channel of the sound card. You'd need a second
    path for another bike. Scaling beyond that is trickier.
    But until you get to needing extra wires, it's the ultimate in cheap!

    Just a thought.

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
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