speed sensor?

>>951821

Come on, nigga, try a little harder. This is basic stuff.

Stick optical encoder on shaft (can be literally just a piece of transparency paper and the optointerrupter from a mouse's scroll wheel). Measure time between pulses. Determine speed by multiplying frequency of pulses by circumference of wheel.

>>951821

Reed switch and a magnet on the wheel would do it.

File: CardInWheel.jpg (61KB, 576x366px) Image search: [Google]

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measure the audio frequency of the clicks...

>>951941
holy shit the perspective of that picture is cringe worthy.

>>951821
usually its just a dot or stripe with an optical sensor pointed at something that rotates.

if its a bicycle like in your pic you can just get a spoke magnet and use a hall effect sensor.

or you can just use your phone on a mount and use the gps.

i have one on my bike right now.
used a magnetic reed switch and arduino interrupts
i have failed using opticalslot and sensors due to sunlight interference and dirt buildup
might post pics later

>>951918
>>951821

https://en.wikipedia.org/wiki/Hall_effect_sensor

>>951822
Actually a better way to do it is to measure the delay between rotations, and index that into a lookup table (or just do the math, if you have the processor bandwidth to do it). That way you get an accurate speed readout after the first full rotation of the wheel.

>>951918
More robust and foolproof than an opto-interrupter, lower power, too.

File: Hall 1.png (112KB, 1024x561px) Image search: [Google]

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hall effect best effect

>>953066

that's way too complicated

all you need is a magnet and an inductor.

you can handle the rest in the software of a microcontroller