I've acquired an old monarch ergo-meter a bit like this....
At the moment it's purely mechanical. I'd like to upgrade it to log the cadence, power and heartrate.
I've got cadence and heart-rate sorted, bit haven't quite got the measurement of power perfected.
Some background... the ergometer works with a friction loaded belt that pulls against the pendulum causing it to deflect. The greater the power the cyclist inputs, the more tension in the belt, the more tension in the belt the more the pendulum moves.
I need to be able to electronically measure the position of the pendulum. I've achieved some crude results with load-cell in the belt that deflects the pendulum. But what I'm looking for is a way of accurately measuring the position of the end of the pendulum.
I think what I need is something like this but more accurate (this one quotes +/- 10%)
Whatever I use it needs to be touch-less, any loading on the pendulum will effect its accuracy, also the top of the pendulum is embedded in a bearing that can't be dismantled, so I can't really measure the rotary position of the pivot, it really needs to be something that can detect the position of the bottom end of the pendulum.
Any ideas?
(I'm hoping for an accuracy of about a degree, or a couple of mm)