Advice on a Project Proposal - Measuring a rowing boats speed

Hi All,

I am considering starting a project and as I have never worked with an Arduino before I wanted to hopefully get some advice as to whether the project is possible from some more experienced people!

BACKGROUND In my spare time I row and race in rowing/sculling boats (think of rowing at the Olympics). As part of the training and racing we tend to use electronic devices to take measurements of boat speed and that market is currently dominated by one manufacturer, NK (see link) however the main problem with their dominance and the fact that rowing is quite a small sport means that the devices we use have literally not changed in the last 10-15 years, there is no drive to incorporate more recent developments in sports like ANT+ or GPS or online tracking and alanysis of . The NK Speedcoach measures boat speed by using a magnetic impeller attached to the outside of the boat, and a coil on the inside of the boat which is connected to the device (you can see under the accessories/wiring harness on the website)

In the last year or two a new option has become available and that is using a smartphone (iPhone in this case) and an App that uses the iPhones GPS to measure boat speed. This is not as ideal solution as the impeller device NK currently provides though as the GPS does not refresh often enough (and is somewhat of an "indrect" measurement) plus GPS is affected by current where as the impeller is not, however using the iPhone opens a whole world of connectivity so you have a lot more space to store workouts, analyse your course using Google Maps, upload your workout live to the web etc

What would be ideal would be if there was a way of connecting the impeller to the iPhone, which is where the Arduino comes in.....

PROPOSAL What I would like to do is use the Aduino to collect the data from the impeller and broadcast it via bluetooth to the iPhone, I would plan to take a non-functioning NK device in order to use the dock and connect the Arduino to that. I would like to make it as cheap and light as possible so I was thinking I could use the mini with a bluetooth plugin

That's where I have got to so far, what are peoples thoughts? Essentially it needs to be able to read the induced current from the impeller and then broadcast the signal so I just wanted to check this is possible before I go ahead and buy everything and start experimenting!

Regarding the programming side advice would be welcome, to start with I was going to check out a couple of Aquarium mods I have seen around on this forum as they also use signals from impellers so it may give me a starting point

The problem with sending data to an iPhone is that the iPhone does not have the serial profile of the bluetooth stack (Android has). Most accessory producers circumvent that by using the keyboard profile or some other workaround. But I am not aware of an Arduino bluetooth module supplying the keyboard profile for example. There are serial connectors (physically connecting to the big main connector of the iPhone) that allow communication with an Arduino device.

Hacking the NK impeller to allow an Arduino accessing it should be that difficult although sometimes "the devil is in the details" (I don't know if that makes sense in English :-) ).

What is the signal level from the impeller setup? you might need to do some signal conditioning to get a clean signal, but that is not very difficult. You would need to figure out some way to calibrate as it might not be linear - more propeller slip at lower speeds, or more at higher speeds...

First piece of info is what the signal looks like and what pulse rate you can expect. Both easily doable on the bench, though you might need access to an osciliscope to see what the signal looks like.

The other option would be a pitot tube setup, though the pressures are quite low and that might be more difficult. Differential pressure and analog to digital conversion. Actually easier to program, though the device might be more of a problem.

Are you trying to measure the boat speed relative to the water, or to the land? They will be substantially different and you need to be clear about which you want.

I suppose that if the impeller based solution has cornered the market it must work OK, but I'd have thought that a pitot tube and pressure sensor was a more robust solution given that the water probably isn't especially clean. The only challenge would be getting a sufficiently accurate pressure sensor - the pressures you'd need to measure would be quite low.