Very Easy Cadence Meter For Your Bike <$12

Step 8 Computer Set Up

This is the set up for this computer.

Hold left and right buttons down at the same time to reset,
the whole display will flash then go to the wheel size.

It will show 2124 the default setting with the 4 flashing.
Change the 4 to a 3 by pressing the right button.
Once it is at 3 press the left button to move the
cursor over to the next number and set it to 3.
Repeat until the number is 3333

It will then go to the KM/Miles mode.
Since it comes up as KM first just press the
left button to set it as that. The right button
will switch it back and forth between the two.

You set the time by holding the left button down for
about 4 sec when the display is showing the time.
You can select 12 or 24 hr mode then you
will set the time, hours and minutes.

If You you mess up just reset by holding both buttons for
a few seconds and start over.

How it works.

Say you want it to read 60KM at 60 RPM's
60km is 1km per minute or 1000 meters.
1000 meters is 1000/60 or 16.666 meters per sec.
Since there are 5 magnets for each rotation 16.666/5
is 3.333 meters per 1/5 second or 3333 MM.

Each time a magnet passes the sensor it is recording
as if it is moving 3.333 meters.

Mountain bikes or comfort bikes with 4 magnets.

16.666/4 would be a setting of 4166

The reason you need this many magnets is that the max
wheel size you can input on this computer is 5999.

I hardly ever have a Cadence above 90 so the 99 limit is
fine for me. You can cut the number in half and
remember to double the readout if you like. That will
set the top limit to 199.8 RPM's

To check your work go to this site and print out
a gear ratio chart using your tire size, front
chain ring, rear cassette size and the cadence
you want. You can cut it out and tape it
on your bike if you like.
http://www.sheldonbrown.com/gears/

Hope you enjoy this project as much as I do.

Comments

[gdl1228]

i have a question will it work on a go cart??? if so, what should i enter as a wheel size??

[Jodex]

It depends on your wheel's size.

[hintss]

I have a bell branded cycle computer. the only thing is that it looks different, but the harness, sensor, and magnet that came with it look the ones that came with yours. It also has 2 buttons, and programs in exactly the same way, showing 2124 as default with 4 highlighted, and you also push the right button and push left to go to next digit. Everything else is also the same. Do you think one brand copied off another?

[kgtateddy]

i dont get why you use 5 magnets instead of just one..... like on the wheel can someone explain me??

[gdl1228]

each gear operates differently it can change the way it calculates the speed

[Phil B]

See my comment below. I used one magnet stuck in the crank arm recess at the end of the left pedal. I programmed the cyclometer for a wheel size of 1667. It worked great. I ignored the decimal point for a direct reading of my cadence. I think the author used multiple magnets so the two display numbers would both be large, not the smaller decimal place number. He said the sun may glint off of the screen and make the smaller number hard to read. I did not have enough wire to reach the handlebar and mounted the display unit on my top tube near the headset. My body shields the display unit from the sun. It worked for me that way. I was concerned that magnets stuck to the caps of the chainring bolts could come off if I hit a big bump on the road. The recess at the end of the crank arm seemed like good insurance.

[LightSpeed1]

Ingenious adaptation of available cheap technology! Thank you for the suggestion. Locally, that bike computer from Walmart (I already have two) sells for under $9 each and is 10x more accurate than many models ten times the price since you can set it to mm circumference (others only do cm). I recommend it. Another alternative is to know what gear you are in and calculate the gear inches of the gear to determine the speed you have to maintain in that gear to be doing your optimal cadence. For instance, my third gear is 83 GI. At 90 rpm cadence, I am going 22.2 mph. If I am going slower, I am under 90 cadence. All I need is to memorize (or make a handy chart taped to my top tube) that number for each gear to have a guide. For 70 rpm, it is 17.3 mph. So to be in my range in third gear, I need to be going between 17 and 22 mph while pedaling. This way one speedometer is all you need. But you have to do the calculation and remember the ranges. Your method is easier to remember. Thanks for your instructable!

[rseymour]

Cool, relatively easy hack. Thanks... added to my list of things to try.

[JJJordan]

Dude, that's awesome, totally geek! I really appreciate it, but it is not as cheap as it looks like (you can get cheap cadence capable cycle computer for less than $40 herehere). But if you already have computer, than this might be your cadence meter... So it doesn't really worth it (except the tickle that you got your bike geeked by yourself) and is not reliable reliable - I think zip ties are one of the greatest human inventions.
Oh, and something else - if you want to have a heart rate monitor too, than your handle bar will look more like the Maltese Falcon dashboard'Maltese Falcon' dashboard

But I really like your "not in a box" style thinking.

P.S. I am not an expert, but I've heard that 90rpms is recommended speed for normal ride, about 100rpms is for sprints and uphills and 80rpms is when you want your legs to rest (at downhill or flat).

[enthusiast]

Very nice project! I'm gonna try it out as soon as possible ;P

P.S. Sorry, can't help but being "Monk'ish" a bit. In the last step the units are a little confusing, the speed is measured in km/h or m/s. I'm sure You know what I mean ;')

[Sailor Bob]

Corrected my mistake in the last part the computer is reading 3333 mm each 1/5 sec. Please let me know how your project turns out.