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I am interested to build a bike but I would also like to have free software/hardware. How can I build a cyclometer with open-source software? Would it be possible to find reflashable hardware or open schematics?

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PCB = Printed Circuit Board? As opposed to mechanical parts? – Neil Fein Feb 17 '11 at 16:41
@Neil Fein: of course, PCB = printed cicuit board. – user652 Feb 17 '11 at 23:07
Okay, changed your title to reflect this. Mechanical speedometers/odometers are quite rare, and a cycling computer is, of course, electronic by nature. – Neil Fein Feb 18 '11 at 0:29
Cyclometers are clearly on-topic. This question is simply unclear as it is currently written, and I want to understand it. Stack Exchange, the company that runs these boards, is very clear about what they are to be used for, and that's asking and answering questions. I'm not trying to ruin anybody's fun. However, questions have to be clearly written or at least understandable, and this one, in my opinion, is not yet there. I'm doing my best to help you, not hider you. – Neil Fein Feb 18 '11 at 2:06
It;s not spam - which is marketing email, by the way - it's an attempt at understanding the question, a legitimate use of comments. – Neil Fein Feb 18 '11 at 2:45
up vote 3 down vote accepted

Easiest platform is probably arduino - nearest bike thing I can find is this

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+1 cool so I don't need to buy a closed code cyclometer, had actually some arduinos around. – user652 Feb 16 '11 at 23:44
At the speeds things happen on bicycles it's very easy to just count the inputs from a magnet+switch with an interrupt. Hardest part is probably a suitable cheap display – mgb Feb 17 '11 at 0:02
@wdypdx22: I have used this beast [1]. Very small and now planning an automatic chain lubricating thing but unsure of your requirements. Check the specs. [1] – user652 Feb 17 '11 at 0:57
There are surface mount nano versions, or there is this – mgb Feb 17 '11 at 2:42
@hhh all the arduino variants are free and open source, they also use the same very simple IDE and language. You can also get arduino clone boards from local makers, some smaller and cheaper. – mgb Feb 18 '11 at 6:10

The most detailed account/details I've come across for building your own bike computer is here on PIClist.

Those pages contain detailed instructions for building a bike computer using a PIC microcontroller linked to a Hall Effect Sensor (it detects the magnet attached to a spoke as the wheel spins). In addition to the build details it also features a detailed discussion of the design process which the creator undertook whilst creating the computer.

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