Monday, April 20, 2015

Garmin Bicycle Speed and Cadence sensor Gen2

Slowly but surely wireless technology is becoming available to the /common man/ and so this is a mini review of the 

Garmin Bike and Cadence Sensor

What is the big Idea then?
The idea is that your GPS smartwatch can figure out your position and speed from the GPS satellites it talks to.

Modern smartwatches I now use e.g. Garmin, provide a Cycle Programme that tracks your cycling and then displays the results including your route, and speed over the route at Garmin Connect

However a slightly more reliable way to measure speed would be to measure the rotational speed of your wheel and knowing its radius calculate the speed that way.

And further to mount a G force sensor on the pedal which would be able to understand your rotational cadence ie pedal strokes per minute

Here is an example:

But wait what about the Watch?

Okay, yes, the GPS watch can also detect the speed but it won't be as accurate and it knows nothing about pedal cadence.

Why Gen2?
Because the first Garmin Sensor, I call Gen1, whilst also using the Ant+ protocol  was a bigger clunkier affair and it needed a traditional magnet passing the crank and wheel to trigger the sensors.

Any other notes?

Yes,  the traditional way to measure speed is mount a magnetic unit on the spokes that passes a sensor mounted on the frame. And similarly for cadence a pedal mounted magnet passing a sensor

Here you see the old and in my opinion more /clunky/ setup. Older but actually using more technologically advanced Bluetooth Sensors, talking to a TomTom smartwatch.  Just to remind myself ... Garmin watches cannot use Bluetooth Cadence, Speed or Heart Rate sensors, even though their smartwatches have  Bluetooth.  Garmin smartwatches use the Bluetooth to talk to your Smartphone only.

 Okay, so these are the components in the box

 The rotational speed sensor mounted on the back wheel

And the Cadence sensor on the left crank

Telling Your GPS Watch
Hopefully you have a fairly modern Garmin GPS Smartwatch in which case you should not have any communication issues.

Your Smartwatch needs to talk the ANT+ protocol to both these units simultaneously.  Bluetooth is not going to help! This is the compatibility matrix

So how practical or fiddly is it?
The idea is basically that you go cycling and always use your Garmin GPS smartwatch.

You have to do a onetime setup step which means connecting your Smartwatch to these particular cadence and speed sensors.  This is a useful step since then the Garmin will ignore any other nearby sensors  (imagine you are in the starting grid of a race with tens of others sensors close by, now it will just pick the right ones)

Now when I start my cycle I

- I switch on my wrist mounted Mio heart rate monitor
- Go outside for GPS reception
- Select Garmin, Cycle mode on my Garmin smartwatch
- Garmin automatically connects to heart rate and cadence and speed sensors

Start Cycling.

- On returning home, stop activity recording
- Plug watch into cradle and it automatically loads data to Garmin Connect and charges back up  (Actually the Watch has WiFi so it can upload all by itself, but the dock charges so I tend to leave it plugged in, go for a shower, and by the time I am changed it's uploaded and fully charged again).

The power sources for these sensors are button cell batteries, supplied with the units, and that I understand should last for about 1 year.

So now the full Garmin report looks much more interesting.

I'm extremely happy with the new sensors.  Whilst they work only with Garmin units, if you have a compatible one and are serious about checking your pedal cadence and absolute speed on your cycles then this is a must.

It's less fiddly that the older combined sensor and means you don't have to attach that magnet to a spoke on your rear wheel.


Errata: This post was initially and wrongly title /Bluetooth Speed and Cadence sensor, because my brain was not functioning.   Garmin supports ONLY the older Ant+ standard and not Bluetooth.

My last sensors were Bluetooth and were from TomTom.   I had hoped that Bluetooth would take over the scene, but it seems not.  (There are standardisation issues for many to one Bluetooth communication that I understand nobody seems to be bothered in solving)