heart transmitter

[newelectr40]

hello new hear wanted to post question on something i have just thought about and looking for some feedback or direction, or whether am barking up wrong tree hope you can help.

i have heart strap which goes around chest, and from what i gather a signal is transmitted from the chest strap at 5khz and picked up by receiver in watch, which processes the signal and displays it.


so when using this set up if the watch is taken certain distance away from chest strap (transmitter) the watch (receiver) no longer is able to collect the signal.


so my question is.

is it possible to build circuit in between the transmitter and receiver, which will receive the signal and amplify it and re transmit the single so that it can be receved at the watch. I was thinking from current knowledge that , first step build receiver i.e coil with resonance of 5khz or tuned to 5khz, then check the signal is the same from transmitter, then amplify with op amp, then re transmit, or is this not possible

thanks hope you can help or point me in right direction

 

[alec_t]

Relaying the signal is doable in principle, but are you sure of the 5kHz figure? I can't believe it's that low.

from current knowledge

Acquired how? Is there a datasheet you can post a link to?

 

[newelectr40]

here link to devices that recives signal from the transmitter belt same as watch does, or this device is in watch, on page 3 it shows the signal is transfered electro magnetic, i think, and on page 5 the reception frequency is 5.5 khz, i think anyway. also on page 3 the is some info on putting device near tv will cause interfernce is the anyway stopping this interference if you are near tv.

https://www.electro-tech-online.com/custompdfs/2013/02/RMCM01.pdf




here some info got from book on polar products

The Polar Transmitters send short signals for each heartbeat to the
receiver. These signals are low-frequency 5 kHz (kilohertz) electromagnetic
fields at very low power, less than 2nW (nanowatts). The magnetic field
strength at the transmitter is 5 uT (microtesla) and 1 nT (nanotesla) at a
1 m distance.


Polar Non-Coded and T31 Transmitters :

Transmission frequency: 5kHz
Means of transmission: On/Off -modulated electromagnetic field with a
5-7ms burst for each heart beat

Polar Coded, T31 C, WearLink 31 C and T61 Transmitters:

Transmission frequency: 5kHz
Means of transmission: On/Off -modulated electromagnetic field with a
train of three 5ms bursts for each heart beat. Time interval coding.

The strength of the electromagnetic field at the transmitter is 5 uT
(microtesla) and 1 nT (nanotesla) at 1 m distance.

many thanks

 

[newelectr40]

double post sorry

 

[alec_t]

So 5kHz it is. I think you will need a very narrow band receiver to avoid response to spurious noise. Your tuned coil idea sounds a good starting point. Presumably that will feed a tuned amp followed by a detector to identify the pulses transmitted. Having picked out the pulses it should be straightforward to pulse-modulate a 5kHz generator.
Here's some info on narrow-band amplification:-
**broken link removed**