Heart rate monitors and gym equipment

[drossall]

A peripheral question if I may.

If I've understood it right, if you're wearing a heart-rate monitor (strap), exercise equipment can pick up the readings and show them on their screens. With a whole gym full of sweaty people to choose from, how does a machine know from which monitor to take its readings?

I assume that there is some initial pairing process, but not I think at each new machine?

[Chris S]

Depends on the protocol - but your device will have an ID that it would be useful to know.

Fboab and I both use BLE/ANT+ HRMs on our indoor trainers - we just have to learn which ID is which. Sometimes if she's trying to pair hers to something, she'll ask me to wander off so only her device shows in the list - I'd imagine a room full of devices is a PITA! Can you pair it to something in the comfort of your own home so you can learn its ID?

[fuaran]

For an Ant+ sensor, it is essentially a broadcast. ie it is just transmitting your heart rate, when it is switched on. So you can have multiple devices receiving that at once. It is handy if you want to use a watch, bike computer, phone, gym machine etc, all displaying your heart rate at the same time.
You just have to check the ID number, to make sure you are connected to the correct sensor.

Whereas Bluetooth LE needs to be paired to make a connection. The heart rate sensor connects to one specific device, ie a 1 to 1 connection. Though some models allow 2 connections at once.

For a gym, I wouldn't bother with setting it up and connecting for each machine. Just take your own watch/phone to display it.

[drossall]

Maybe I've got the wrong impression. I don't have a sensor of my own at this moment. I'm trying to work out whether it's worth it. However, I'm using chest straps that are issued to me in cardiac-rehabilitation physiotherapy sessions, and there it does work as I describe; we go into the gym and our heart rates show up on whichever piece of equipment we move to. No doubt they've done some advance set-up. Somehow I got the impression that that can happen for gym members in general.

[grams]

Some receivers are, erm, promiscuous and will show data from any device in range. Some need specific pairing and will only show data from devices that have been setup.

[drossall]

So how do the promiscuous ones know to show my heart rate and not the one from the fellow on the next machine along? Because it does work in the physiotherapy sessions.

I'm using a key of course, so the machines "know" which person is using them.

[Greenbank]

So how do the promiscuous ones know to show my heart rate and not the one from the fellow on the next machine along? Because it does work in the physiotherapy sessions.

Signal strength probably.

If signal strength falls away at the square of distance then a signal 0.5m away is going to be 9 times stronger than a signal from 1.5m away (assuming equal transmission power).

[Kim]

I'm using a key of course, so the machines "know" which person is using them.

I'm guessing the database includes the ID of the sensor, then.