looking for help with heart rate transmitter please

[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

 

[magvitron]

designing a good antenna for the transmitter is a good idea.. and adding a stage of power amp (tuned) may increase some dbs.

 

[MikeMl]

You are trying to build a "repeater", a device that receives a signal and retransmits it at the same time. That works, as long as the transmitter doesn't transmit on the same frequency as the incoming signal. That type of operation is called "duplex". The frequencies used in duplex operation have to differ by at least a few percent. You would have to modify the receiver to operate on a new frequency.

The only way to build a "simplex" repeater (one that receives and transmits on the same frequency) is to make it a store-and-forward system, which only works if the original transmission consists of short messages with dead time between them.

 

[cachehiker]

It sounds like a Polar Hear Rate Monitor. IIRC, they use a form of magnetic signal coupling between two coils. Being micropower in nature to extract decent battery life out of a coin cell, their range drops off precipitously as you've already noted. They're also very sensitive to the orientation of the transmitter relative to the receiver.

Although the exact communications protocol is pretty simple, I don't believe Polar has ever released it in an application note. We've used their RMCM01 receiver but I don't think anybody here actually signed a non-disclosure agreement involving details of the communication protocol. There are a couple of tinkerers here playing with these though:

Polar Heart Rate Monitor Interface