How does this chest strap heart rate monitor thing work?

October 15, 2012 1:16 AM

Are chest straps that come with heart rate monitor watches interoperable with other devices / a different brand of watch? What wireless technology is allowing the chest strap part to communicate with the wristwatch part?

Of course I went with the cheapest such watch at walmart, so there wasn't really any exhaustive documentation of the technical specifications in the packaging. The brand is "sportline" and I think it was a model they're no longer selling -- can't find it on walmart or sportline's websites, but I think it is on amazon. And a reviewer at amazon mentions the strap's compatibility with machines at the gym.

Through some googling I've found some weak evidence that something at-best vaguely designated as "5 kHz" might be considered the industry standard heart-rate transmission technology. The only other possibly competing technologies I'm aware of are bluetooth and something else called ANT+.

Bottom line: does anyone know if one could buy, for example, a used polar watch and expect it to work with this "sportline" strap?

... and might there be any kind of receiver that one could plug into a smart phone in order to capture this data? (I imagine the best solution for this sort of thing is just to buy a bluetooth transmitter chest strap)

posted by vcnt to health & fitness (7 answers total)

It's a bit more complicated than just picking up the radio signal. IIRC the band you put around your chest transmits a low-frequency, low-power "pulse" when a heartbeat is detected. Here (pdf) is a datasheet.

It's a cheap and dirty (and ultra low-power) AM radio signal so it has to be filtered and cleaned up on the receiver end (where it is also easier to replace a battery.) There are some kits available.
posted by three blind mice at 1:34 AM on October 15, 2012

Short answer: Yes, sometimes, depending on whether or not the monitor and display use any kind of proprietary encoding. Generally the cheaper monitors and displays use the standard format.

You're right that the best way to get data onto your phone is to go with bluetooth (although there may be a widget that plugs into the iPhone), but if you mostly just want the recording functionality it's better to skip the phone altogether and use a dedicated heart rate logger. It's cheaper and less prone to the battery dying.
posted by anaelith at 2:25 AM on October 15, 2012

Zephyr make a bluetooth device called HxM which works well with lots of Android smartphone apps. The advantage with an app over hardware is that you get constant new features!
posted by devnull at 4:09 AM on October 15, 2012

>Bottom line: does anyone know if one could buy, for example, a used polar watch and expect it to work with this "sportline" strap?

Having owned a couple over the years I can tell you that a particular polar watch will not necessarily work with all polar straps, never mind with some other brand. You will need to give it a try.
posted by w.fugawe at 5:13 AM on October 15, 2012 [1 favorite]

Even within the Polar product line, there are a number of compatibility issues between transmitters and receivers, so I'm not sure that the fact that the device may or may not use 5 kHz means it will work with any given receiver. ANT+ is a pretty well-defined standard
posted by Lame_username at 5:15 AM on October 15, 2012

It is really a crap shoot. Many athletes have 3+ straps because of different communication protocols, but the most widely available is the Polar uncoded because the spec was readily able to be reverse engineered for third parties. The coded straps helped avoid picking up another person's signal, which is useful in a group exercise situation.

I would return it and buy something that comes with the HR strap to be sure.
posted by dgran at 5:40 AM on October 15, 2012

High-end polar belts have "unique" frequencies to avoid interference with other heart monitors and thus aren't even detectable by other high-end polar watches.
posted by Obscure Reference at 7:10 AM on October 15, 2012