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The Magic Cafe Forum Index » » The Science of Magic » » Heart Rate Monitor Watches - Transmitters (0 Likes) Printer Friendly Version

tommy
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Heart Rate Monitor Watches - Transmitters


There are many makes of these things:

http://www.dietandfitnessresources.co.uk......ving.htm


When at the gym, where a number of people might wear these monitors in close proximity, how do they stop the monitors from getting confused and reading another’s heart rate?

What type of signal do heart rate monitors use to broadcast their heart rate (data) to the watch?

Is it a radio wave? If so what frequency?

If you wore the transmitter an I wore the watch could I read your heart rate if we were a few feet apart?
If there is a single truth about Magic, it is that nothing on earth so efficiently evades it.

Tommy
Craig Matsuoka
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If they're using the kind of inexpensive wireless modules that I think they're using, the data link is probably not very sophisticated and very short range (no more than a yard or two). These rf chips share the same frequency (916.50 MHz) and modulate via amplitude-shift keying, so they're vulnerable to the same interference and crosstalk problems as AM radios. Distance is really the only thing that keeps them from interfering with one another.

Assuming these monitors aren't using more sophisticated multichannel or FM modules, you could probably read someone else's monitor with your watch. That is, if it's the same model and you can manage to linger close enough (arms length) without creeping the person out. The only way to know for sure is to try it.
tommy
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What I was dreaming of doing was hiding an heart rate transmitter in a chair and wearing the watch so I could see the heart rate of he who sat in that chair. Don’t think it can be done though from reading this:

ECG-Accurate Monitors with Chest Strap
The most accurate heart rate monitors use a chest strap which fits snugly around your chest just below the breast. The transmitter detects the electrical activity of your heart just like an ECG. It relays this to a display, usually worn like a wristwatch, although some use earphones instead. It is important for the strap to maintain contact or you get wild readings.

Pulse Monitors Without a Chest Strap
These monitors work by detecting your pulse - usually by placing one or two fingers on sensor buttons. They cannot give you a constant reading of your heart rate, you have to take it on demand instead. They are also trickier to use than the chest strap monitors - cold fingers, etc. can give you no reading or wild readings.
If there is a single truth about Magic, it is that nothing on earth so efficiently evades it.

Tommy
Justin Style
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Hi, I just happened to be wondering past this room on my way for some coffee, and I couldn't help notice this topic.

As you may or may not know, I am an avid bicyclist and I ride several thousand miles per year. I wear my heart rate monitor 90% of the time. I wear the chest strap monitor and the wrist watch receiver - POLAR Heart Rate Monitor.

The distance from the monitor and the receiver is an arms length. However, after I get done with my ride and take off the watch, lay it on the desk It will still transmit, but not from more than five feet away.

I don't know if this helps with what you are trying to accomplish, but I thought I'd give my perspective.


Also, If you work out or are planning starting an exercise routine, I STRONGLY recommend wearing a heart rate monitor. Learn what your target heart rate should be and work out in that for maximum results from your effort.

Good luck!
Christophercarter
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The cheaper models do often interfere with one another. Until I upgraded recently I would frequently be showing the heartrate of the person on the treadmill next to mine. Depending on conditions I would guess the typical range of the transmitter to be up to six or seven feet.
Enzo
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Quote:
the data link is probably not very sophisticated and very short range (no more than a yard or two). These rf chips share the same frequency (916.50 MHz) and modulate via amplitude-shift keying, so they're vulnerable to the same interference and crosstalk problems as AM radios. Distance is really the only thing that keeps them from interfering with one another.


I work with HRMs professionally and nowadays a lot of HRMs have coded transmitters. This means that the signal will not interfere with signals from other HRMs. For instance Polar has coded transmitters even for their cheapest models (although they also sell them with uncoded transmitters which will interfere).

Actually the HRMs I use (Polar) do have quite a sophisticated broadcasting scheme. This is because the breast band is molded in one piece and the battery cannot be replaced. Therefore it has to be extremely energy-efficient. The polar HRMs I use transmit 5kHz (so not RF) very low power (2nW) pulses. They only transmit a brief electromagnetic pulse for each detected heart beat, so there's no continuous transmission.

So Tommy, for what you want to do the biggest problem will probably be the distance. These monitors have been designed to be worn on the wrist or to put on a bike. According to the manual, the Polar transmitters have a range of 3 feet. When we do 24 heart rate recordings, the patients have to wear the watches and cannot put them on their night tables. I am not aware of any HRMs with a larger range.

But would it be a problem to stay within 3 feet of the person sitting in the chair? Wouldn't it be a bigger problem to secretly obtain a heart rate reading? I suppose in your idea you couldn't use a chest strap anyway. You could maybe have them hold an object in which you conceal a pulse monitor's electrodes. These are used frequently in treadmills in the Gym and, as you say, they work only if the hands are not too dry. But that shouldn't be the problem if someone is a "victim" from the audience, should it?
amyliao
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Quote:
On 2008-03-13 23:58, tommy wrote:
Heart Rate Monitor Watches - Transmitters


There are many makes of these things:

http://www.dietandfitnessresources.co.uk......ving.htm


When at the gym, where a number of people might wear these monitors in close proximity, how do they stop the monitors from getting confused and reading another’s heart rate?

What type of signal do heart rate monitors use to broadcast their heart rate (data) to the watch?

Is it a radio wave? If so what frequency?

If you wore the transmitter an I wore the watch could I read your heart rate if we were a few feet apart?



I am looking for Bluetooth Heart Rate Monitor for a long time. Finallyl, I find it from KYTO. It is great with reasonable price(USD45/pc). If you guys interest in it,u can contact amy at kytoelectronic dot com. Their service is also very good.
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