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Comment by exelius | Hacker News Reader

Also, a standard inductive sensor (i.e. a magnet attached to a spoke and an inductor) attached to the raspberry pi would be a much better option.

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The benefit of taping a piece of paper to the wheel is that you could apply the same technique to something like a treadmill where you wouldn't want a magnet to be traveling along with the tread. The benefit of Arduino is lack of OS overhead/risk.

If you are going with a visual piece of tape, then you could replace the arduino with a simple mobile app that recognised the tape via camera and transmits speed via UDP to the app. I wonder if the camera on a typical phone could keep up ?

You could do the same with an inductive sensor wired to the headphone jack. This worked for Square to read magstripe data, which is significantly more complex of a signal to parse than simply counting the number of local maxima per second.

Inductive sensors are cheaper, simpler and more foolproof; cyclists have used them for decades to gather both wheel speed and cadence.

Slightly off topic: You make an interesting point about Square. In the context of Apple Pay, the move to take away the headphone jack suddenly makes a lot of sense (for Apple).

I don't know about that; the cheap Square reader is a piece of crap that is really just a "starter" product (they're not well-made and fall apart after even moderate use). Anyone who swipes more than 2 or 3 cards a day would be better served by one of Square's commercial readers -- all of which connect via Wi-Fi, Bluetooth or the Lightning port.

Also, Apple would certainly include a Lightning->Headphone adapter that would also be usable for card readers. They just use the line in from the microphone.

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