Bicycle Speedometer

With my customization of my bike, I just have to have a speedometer. But, I haven't found a single place on the Internet showing how to make one, just how to buy one.

I know that speed = distance/time. I was thinking, since this is going on my bike, I could measure the circumference of the rim and hook up a circuit that would have a something (motion detector?) on the front brakes and another something on the rim, the one on the brakes counting the number of RPMs. I could have it hooked up to a timer, and it would have a digital read-out, which would calculate the speed, that updates every certain number of RPMs.

Has anyone ever built a speedometer, or if not, do you think something like that would work?


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har946 years ago
can anyone suggest any other ways that do not use any sensors.....
i was thinking of making it on the lines of galvanometer or ammeter using a dynamo.....but i have a problem in calibrating the scale....
If a DIY approach is essential, then a reed switch would indeed be the way to go. Or a hall effect sensor. Both use a pretty strong magnet mounted on a spoke (typ. on the front wheel).

Finding a hall effect sensor is pretty easy, if You can take apart a PC cooling fan - these are stepper motors, and they have a small circuit built inside them - that's the HE sensor. Find a datasheet to know what to connect where. They usually cover a rather wide range of supply voltages (5-12V?).

A magnet can be taken out of pretty much anything - a small speaker, a hard drive, whatever. Just make sure it gets picked up by the detector circuit (reed switch or HE sensor) at higher speeds, and place it so that it generates a short signal only, when directly aligned with the detector.

It doesn't really matter that much if it's a HE sensor or a reed switch (ofc. using a reed switch makes the whole design a bunch more simple, but whatever strikes Your fancy). The point is to connect this to a microcontroller hooked up to a display.

When that's done, two things are left: getting a time reference, and counting the rounds. The rest is pretty straight-forward -- calculating the speed and displaying it on the display. Getting a time reference can be made easy by using an counter input pin of the microcontroller in conjunction with a clock crystal (the small tubes in quartz clocks). The rest should be fairly straightforward. :-)

(this post for the reference of people finding this result through Google, like me)
Lftndbt10 years ago
Fairly costly parts for something to read speed... Not to dampen your spirits but... I was thinking of doing the same on my bike, until I realised that the bike shop had them for $5... Mine reads speed, distance travelled,avg seed, top speed etc. Maybe pays thte $5 to get the sensors/screen then mod it to suit your style... The screen detact unit is the size of a coin so it would be easily modded...
Goodhart10 years ago
I would think one could put together a gear driven situation also fun directly from the rim or down at the hub.
guyfrom7up10 years ago
can't you do something like this to one of the sprockets?
Hall effect sensor, not a FET, or a simple reed switch. How about hacking a hot wheels radar gun? Not sure of the range, but mount the transceiver from the axle nut and angle down slightly (keep theta small) move the display up to the handle bars. etc.etc.
> Hall effect sensor, not a FET . Thanks for the clarification.
NachoMahma10 years ago
. I tried speedometer +circuit in Google and found a bunch of interesting stuff.
. It sounds to me like you have the basic principle, now all you need to do is figure out how to put it into practice. Most of the ones I've seen place magnets along the rim and use some type of sensor (FET?) to see the magnets as they fly past. A freq-to voltage converter feeds a meter display.
Bran (author)  NachoMahma10 years ago
Of course! I was searching make + speedometer. I always search for the wrong thing. Thanks, Nacho!