Heart rate monitor pickups the heart beat and transmit? How is done?

[[email protected]]

I would like to know in details how a Polar or Mia Heart Rate Monitor
(HRM) pickup my heart beat and how it transmit the signal.

1) I want to know why does the HRM need moisture?

2) Why the paralleled grooves are important on the transmitter side of
the HRM?
There are two, one on each side of the transmitter?

3) What is the wave length of the HRM?

4) Is the length of the plastic "wings" are important for the
transmitter or the pickup of the heart beat?

Does the antenna use a Yagi or coplanar antenna for the transmitter
and for the reception?

5) Has every knows the heart is submerged in a saline fluid where only
Ultra Short wave length can reach the heart due this saline solution.
How does the HRM picks up the heart beat?
Is it by induction?
Is it by conduction?
Is it by using OPamps?
etc

6) How does the electronic circuit works on the transmitter and
receiver side?

7) I've checked the length of the strap and I was able to verify that a
regular cleaning improve the transmission and low down the interference
level? why?

8) How is the transmitter ?receiver encrypted? Is it the ASK code? or
other ?

9) Is there a HRM which can download directly its data to a laptop
through the infrared port?
Guy (gnh888)

 

[[email protected]]

Answers:

1. The HRM transmitter needs moisture on the electrodes to make a good
electrical connection with your chest, where it picks up the small EKG
signal from your heart.

2. I guess that the grooves are to hold the moisture in place by
surface tension.

3. Polar's website doesn't mention the details of the wireless link.
The antenna may be a small loop similar to those used in pagers. Check
this:

http://wireless.fcc.gov/services/index.htm?job=service_home&id=personal_radioso

4. I guess that the length of the wings was chosen to pick up the best
EKG signal.

5. The heart's signal is detected by current conduction directly
throught the chest. It is then converted to wireless by the
transmitter.

6. No info.


7. Cleaning the strap improves the electrical connection to your heart
and reduces EM interference from other sources such as power lines - it
should not affect the wireless transmission or reception.

8 & 9. No info.

 

[Marte Schwarz]

5.> Is it by induction?

Is it by conduction?
Is it by using OPamps?

google around--- ECG-Amplifier.

6) How does the electronic circuit works on the transmitter and
receiver side?

The simple ones uses a 3 kHz oszillator that is triggered once a heartbeat
(QRS-Complex. See slaa280 by ti.com. There is a little overview about ECG
and signal processing. But be careful, there is a lot of garbage in it too
;-)

7) I've checked the length of the strap and I was able to verify that a
regular cleaning improve the transmission and low down the interference
level? why?

Your Skin (everyones) produce fat to save the surface. Fat doesn't conduct
well so remove this will improve the contact, cleaning the skin too.

8) How is the transmitter ?receiver encrypted? Is it the ASK code? or
other ?

Newer system use multiple pulses per QRS-complex. They are coded to separate
pulses from several systems.

9) Is there a HRM which can download directly its data to a laptop
through the infrared port?

Don't know. I saw a schematic few years ago, one guy uses Soundcard as
interface with a simple 3 kHz LC-Antenna

Marte