# DIY Bike Computer



## m85476585 (Jun 7, 2007)

I originally set out to build a cadence-only computer for my bike, since I already have a computer that does the standard stuff, and I'm studying electrical engineering, so it's more fun/challenging to build one than just buying one. I'll probably still build the cadence only computer, but as I've been researching it, I also want to build a more ambitious computer, specifically one that measures power output among other things. So I've come here to ask: If you could have any features in a bike computer, what would they be? Here are some of my ideas:

Of course I will have all the standard measurements (speed, time, distance, including max and average). 
Cadence is easy since it's just another rotation sensor.
Power output will be challenging since I will need strain gauges and a wireless transmitter on the cranks.
Ambient temperature would be easy
Humidity (though the sensor is kind of expensive at $16)
 Barometric Pressure (altitude)
I have a 3 axis accelerometer and 3 axis gyro (roll, pitch, yaw), if that would be useful for anything
Compass?
GPS is probably not worth the effort
Data logging (to download to a computer later) is difficult but I'm working on it for another project
Heart rate (not sure how to do this one)

My main goal for this project (if I ever have time to actually build it) is an affordable power output meter, and anything else is just an added bonus for me. I have no plans to sell this, and everything will be very hacked together on the bike.


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## KINBOY (May 23, 2004)

Good luck, I know the journey is often the reward but making this viable and in a robust package will be hard. 

I would try to tackle one thing at a time, power meter would be it and sort out how to sync it to a already made receiver. 

KIN


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## Harold (Dec 23, 2003)

I don't think the accelerometer/gyro would have much use in a bike computer. I could potentially see it being used to measure hill gradient, but that's about it.

might be interesting to see a humidity data field on the computer. I can't think of any major challenges for that one aside from the cost-as you mention.

compass would also not be that useful. digital compasses need to be calibrated often, which is a software thing, and is going to make your job very difficult.

altitude through a barometer would also be challenging because you have to calibrate the sensor. If all you're doing is showing a readout of the absolute barometric pressure with maybe a graph over time (if you can figure out the datalogging aspect), then it's not going to be so bad. BUT, you'll have software challenges when attempting to translate that barometric pressure into elevation readings because calibration is necessary to adjust for changing weather patterns.

I'm not terribly sure about HR, either. you'd have to look at the HRM strap you'd like to use, and choose a wireless receiver protocol to match. ANT, bluetooth, whatever else. Since you might be having an ANT receiver already for the power meter, it might be worth a shot.

I think I've seen folks do basic DIY GPS receivers. making one that just reads coordinates wouldn't be a huge challenge. but writing the software to give the GPS additional functions would be a big challenge, probably moreso than the other sensors.


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## erginguney (Dec 30, 2005)

m85476585 said:


> If you could have any features in a bike computer, what would they be?


The two that I can no longer live without are:


Grade of the current slope
Cumulative elevation gain

I don't think I'll ever buy another bike computer after this that doesn't show these two.


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