I know very little about electronics so I was hoping to get some advise on a small project I want to do at home.
My home treadmill already has the standard dashboard that tells me the mph I'm going, time and so on, however it doesn't offer any way to get at that information - as you'd expect no dev kits, ways of accessing the data via bluetooth etc. etc.
So my plan is to build a cheap sensor that would measure the speed of the belt. For this I've got the following in mind:
- A small square with some kind of high visibility sticker/paint on the belt.
- A way of tracking the belt paint passing the camera lens, or preferably something cheaper than a camera lens. (This would be calibrated to know how far a second represents on my treadmill).
- Battery-powered by AA/AAA batteries.
- A wifi chip that broadcasts the information it gets from the sensor. I haven't figured out how this will be configured to join my wifi network.
Now the question - is there some kind of cheap sensor that could do the tracking? And is my sketchy idea feasible?
I don't want to have to open up the engine or attach wires to the existing sensors, I'm hoping to build something that's entirely independent.
Answer
There is almost certainly some part of the motor mechanism that is accessible and which can be used to return a periodic signal. This could be eg
- a rotating shaft with a "bump that will trigger a magnet plus Hall sensor,
- or the flywheel on the motor which will probably have some part which differs enough to trigger a sensor.
- or the flywheel surface can be given a white soot of paint etc or a strip of reflective tape to trigger an optical pickup.
You can buy optical tachometers which will repond happily to a periodically varying surface and the silvered tape trick is a standard one with them.
Some of the available tachometers will have some form of output (RS232?) or will be more acceptably hackable than the treadmill.
OR you could build your own without too much effort:
Another home made optical tachometer
More complex crcuit than is needed but the front end gives ideas.
This (from above) plus an Arduino is about enough - or just the sensor with care.
Arduino in the sky with clothespegs - actually a really simple optical interface optical tachometer with Arduino based optical tachometer with numerous clothes pegs assisting.
Wow !!! - Vast list or Arduino application with link to above project (at least)
Sample of commercial unit - Australian seller $A80 rtail. I have one of these. Goes OK. No external interface. Hackable.
Identical unit at Farnell UK 43 GBP ;-(.
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