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OHR - LED intensity and sensor 'depth' cause of issues? Increase led-strength?

Basically the way the OHR works is by emitting light from the leds, and the sensor checking how much is absorbed by blood-flow and how much is bounced back, right?

So I own two of these devices, the TomTom MultiSport Cardio and the Garmin Forerunner 235.

The TomTom MultiSport Cardio has always worked great for me. No cadence issues, almost instant hr-change (with intervals for example) adjustment, only very occasional weird spikes/readings, performed fine in colder weather.

The Garmin, well... pretty mediocre to crappy still. Cadence locks (still with the latest updates, though less frequent it seems). Adjusts crappy to changes in HR, weird spikes/readings and especially in colder weather.

So checking the physical sensors themselves I noticed two things:

1. The led-lights on the TT MSC are way brighter then the FR235 ones.

2. The sensor (and leds) from the TT MSC are way more on the surface (and thus directly on the skin) then the FR235. On the FR235 they lie a bit deeper, in their own 'holes'.

So basically I think this might well be the cause of many reliability-issues. There is less light to work with and less direct contact leading to extra losses and noise.

For ideal skin/veign combinations and situations this might not matter much, explaining why there are also plenty people without issues, but it would be way more susceptible to issues and uncertainty.

Changing the physical location of the sensors/leds is no option of course (actually thought about it, but seems the watch is glued together as opposed to screws so I'll be leaving that alone), but could Garmin increase the led intensity by adjusting the current or something for the leds? (at the cost of battery life, sure, but I think this would mainly be necessary with activities and surely not the 24/7 stuff and I would gladly sacrifice a bit for better readings. Can't imagine it would make an enormous impact either compared to the screen for example).

Any thoughts on this? Will try and get a proper picture of the differences between the two watches this evening..

0 chunkywizard over 9 years ago

Do you think they haven't tested this? I am sure they would have tried lots of different combinations and worked out the optimal design for them as a balence between performance and power consumption. TomTom uses a different design and they will have chosen a different balance. I am sure they would have had a look at what was on the market and have decided their way is best!

Just my 2ps worth

CW

0 FlipStone over 9 years ago

Do you think they haven't tested this? I am sure they would have tried lots of different combinations and worked out the optimal design for them as a balence between performance and power consumption. TomTom uses a different design and they will have chosen a different balance. I am sure they would have had a look at what was on the market and have decided their way is best!

Just my 2ps worth

CW

One would assume so but given the history of sw and fw updates with this watch it's actually hard to tell if, how and how much they have tested things.

And them deciding at a certain moment that a solution is the best doesn't mean it actually is... Just telling what I noticed and what I think contributes to the problems (and might contribute to a solution). Not expecting anything of it actually, but at least it's out of my system so to say, and who knows. Maybe someone might actually think of something clever ;)

Again, love the watch... Which is why I don;t really want to go back to the TomTom, but the OHR would almost make it worth it.

0 Former Member over 9 years ago

I've just updated my FR 235 which was still running an old firmware version. The brightness of the green LED's is much lower than before. This will no doubt help battery life, but I've also got more problems with optical heart-rate reliability (the 24/7 monitoring is at least better, that's something).

0 Former Member over 9 years ago

Interesting comparison work, but I would caution from drawing too many conclusions and attempting to "reverse engineer" design solutions in this way. It instinctively makes sense that a brighter light would be more effective, but there are so many variables in play. We don't know anything about the sensors each watch is using or if there are variations in sensitivity. And we also don't know if each product is using a different algorithm to process that may or may not account for light intensity.

And, at the end of the day, these watches are not user-serviceable (particularly complicated because of water resistance), so I think any learnings to this effect will have limited usefulness as well.

0 FlipStone over 9 years ago

Interesting comparison work, but I would caution from drawing too many conclusions and attempting to "reverse engineer" design solutions in this way. It instinctively makes sense that a brighter light would be more effective, but there are so many variables in play. We don't know anything about the sensors each watch is using or if there are variations in sensitivity. And we also don't know if each product is using a different algorithm to process that may or may not account for light intensity.

And, at the end of the day, these watches are not user-serviceable (particularly complicated because of water resistance), so I think any learnings to this effect will have limited usefulness as well.

Of course more variables are in play, but this is one of the most basic and direct things... Improve the source and all the rest will become easier as well.

And yeah, we completely depend on garmin with this but thought it might be fun (if at all possible) to experiment with this. Haven't given up completely on this yet, just have no clue atm on what I could use for this (without messing with the watch itself).