Bicycle Mechanics - cycle comp driving me bonkers

My cyclocomputer (odometer) has recentlystarted to measure double the speed. I have no idea why it's happening, except I *think* it's happening when the temp goes over 12 or so degrees C. I tried disengaging it from the cradle, resetting it, and a number of combinations of the above.

Then, after a while, it would work OK again.

This erratic behaviour started now at the beginning of spring. I cycled most of the winter with this cycle comp.

I also tried adjusting the magnet on the spoke a few mm lower, or to the side, but it had absolutely no effect.


Any idea? The cyclecomp is branded "Union 10", if that's of any help.

New battery?

New battery?

Thanks. I doubt this, because one of my debugging attempt included replacing the cyclecomp with an identical one I bought for the MTB, whose battery is/was even more worn out - the LCD barely showed anything - and in fact, today I noticed that it finally died - but it still measured the correct speed/distance.

Still, I don't completely rule out the battery theory, just think it's quite unlikely.

Nearly all cyclocomputers (with the exception of some early Avocet models IIRC) work with a reed switch which gets activated by the magnet..

sounds like your reed switch might be wonky, perhaps with a bad connection that gives an intermittent signal which the computer is interpreting as multiple circuit closures for every 'real' triggering of the switch.

Perhaps you should try a new harness and sensor.

EDIT: nevermind, read your second post... hmm.. is your wheel diameter set correctly on that computer?

magnetic field sometimes passes the sensor 2 times on each rotation of the wheel, try moving the magnet close, farther away or up or down the spoke.

also if the magnet and sensor are to low on the fork this effect will be worse because the magnet is moving slower.

also if the magnet and sensor are to low on the fork this effect will be worse because the magnet is moving slower.

Not so--one revolution of the wheel is one revolution of the wheel, regardless of what point of the radius you're measuring it from.

If the magnet's orientation is N-S or vice versa parallel to the line of rotation, then the N and S will trigger the reed each time it passes, leading to 2 activations per pass whereas if N-S is perpendicular, then it's once.

To all you guys who were thinking aloud about magnetic fields and reed relays; thanks for the effort, but as I sadi, as part of the debugging process I swapped out the cyclocomp (I have an identical one on the MTB), and that worked fine. So it's not the "aquisition/sensor" part of the system that is broken.

Nearly all cyclocomputers (with the exception of some early Avocet models IIRC) work with a reed switch which gets activated by the magnet..

sounds like your reed switch might be wonky, perhaps with a bad connection that gives an intermittent signal which the computer is interpreting as multiple circuit closures for every 'real' triggering of the switch.

Perhaps you should try a new harness and sensor.

EDIT: nevermind, read your second post... hmm.. is your wheel diameter set correctly on that computer?

Yes it is: it measured the correct speed all its life - it's only now, and only sometimes, that switches to "double-speed mode".

Is it wireless or wired?

Nearly all cyclocomputers (with the exception of some early Avocet models IIRC) work with a reed switch which gets activated by the magnet..

sounds like your reed switch might be wonky, perhaps with a bad connection that gives an intermittent signal which the computer is interpreting as multiple circuit closures for every 'real' triggering of the switch.

I think you might be on to something here. I would actually try to "de-tune" the magnet, given the symptoms. The reed switch could be bouncing and giving a double reading.

Move the magnet a cm further away from the sensor and see what happens.

[You are the 'robo' !!!]

I think you might be on to something here. I would actually try to "de-tune" the magnet, given the symptoms. The reed switch could be bouncing and giving a double reading.

Move the magnet a cm further away from the sensor and see what happens.

[You are the 'robo' !!!]

http://www.bikeforums.net/showthread.php?p=4145351#post4145351

http://www.bikeforums.net/showthread.php?p=4145351#post4145351


Yah, ok, so have you actually tried moving the magnet? You have not said that you did. My computer just stopped working one time and it turned out that I removed the wheel to true it and re-installed it backwards (i.e. the magnet was on the wrong side of the wheel). I had removed the QR to grease it and re-installed it wrong.

Lot's of problems have simple solutions (= Occam's Razor). Maybe your magnet got whacked and it's not where it used to be.

Yah, ok, so have you actually tried moving the magnet? You have not said that you did. My computer just stopped working one time and it turned out that I removed the wheel to true it and re-installed it backwards (i.e. the magnet was on the wrong side of the wheel). I had removed the QR to grease it and re-installed it wrong.

Lot's of problems have simple solutions (= Occam's Razor). Maybe your magnet got whacked and it's not where it used to be.

It shouldn't matter, because an identical cyclocomp works fine when placed in that same cradle. If I had done some magnet-related problem, it would have shown with the other (identical) cyclecomp as well, but didn't. So, it's not the magnet-reed relay-cable-cradle assembly at fault (= Occam's Razor).



But regardless, in my first post (just to satisfy your curiosity) I state that yes, I have dicked with the magnet, too:

I also tried adjusting the magnet on the spoke a few mm lower, or to the side, but it had absolutely no effect.

I did that because it was the most obvious thing to do, and the simplest thng to try.

It shouldn't matter, because an identical cyclocomp works fine when placed in that same cradle. If I had done some magnet-related problem, it would have shown with the other (identical) cyclecomp as well, but didn't. So, it's not the magnet-reed relay-cable-cradle assembly at fault (= Occam's Razor).



But if you had read my first post (just to satisfy your curiosity); yes, I have dicked with the magnet, too:

I also tried adjusting the magnet on the spoke a few mm lower, or to the side, but it had absolutely no effect.
What's up with the attitude? People here are trying to help you.

It shouldn't matter, because an identical cyclocomp works fine when placed in that same cradle. If I had done some magnet-related problem, it would have shown with the other (identical) cyclecomp as well, but didn't. So, it's not the magnet-reed relay-cable-cradle assembly at fault (= Occam's Razor).



But if you had read my first post (just to satisfy your curiosity); yes, I have dicked with the magnet, too:

Well, by all means, go for the extremely complex solution to your problem. Cosmic rays ..., whatever.

What's up with the attitude? People here are trying to help you.

No, not wireless.

It shouldn't matter, though, since when I replace the cyclecomp, it works fine. So all parts being the same except for the cyclecomp, the speed measurement is fine - logic / basic debugging dictates that the problem is located in the cyclecomp itself, not the system that brings the rotation signals to it.

So far, I put the most hope in the dying battery theory. That, or it's cosmic rays.

Well, by all means, go for the extremely complex solution to your problem. Cosmic rays ..., whatever.

You know what, this is really simple: you asked whether I tried moving the magnet this way and that way, and I said I did (I said so in the first post in this thread).

OK? Still mad?

Well, if the problem is internal to the computer, you're pretty much screwed..

I guess the one other thing you could check would be the contacts between the computer and the cradle. Again, if one of them was getting an intermittent connection, it could have the same effect as a misoriented reed switch or poor connection down there.

Other than that, time for a new computer.


(oh, and it's not set to km/h is it? :p)

Well, if the problem is internal to the computer, you're pretty much screwed..


I know! Unless it's low battery voltage - but that didn't seem to affect the other cyclecomp while it was still ticking. Hey, I just got an idea: I'll move the battery from the intermittelntly-not-working-correctly citybike cyclecomp, into the MTB cyclecomp (which worked well all the way till the last Coulomb of charge from the battery was dispensed), and see what that does to the MTB cyclecomp. It also could be that the citybike cyclecomp, although exactly the same make and model (even bought the same day), might be more susceptible to low battery voltage.



I guess the one other thing you could check would be the contacts between the computer and the cradle. Again, if one of them was getting an intermittent connection, it could have the same effect as a misoriented reed switch or poor connection down there.


I thought of this, and hence cleaned the contacts on the cradle and the cyclecomp. And then removed and reinserted the cyclecomp dozens of times, but that never helped one bit.

Remember, the problem is intermittent in the way that it will be measuring double speed for a while, then after a couple of hours (maybe because the temperature went down) it would work fine again, and there is no way for me to make it work fine when it's actung up, or make it work wrong when it's working fine.




Other than that, time for a new computer.


Yeah... will try a new battery first.




(oh, and it's not set to km/h is it? :p)

Of course it is :) Km/h all the way. Always has been, always will be (unless I move to the US).

Yeah... will try a new battery first.

Well, my reading comprehension was clearly down when I thought I read this thread last night. Do you think it might be a weak battery? I foolishly assumed that that was the very first thing you tried. Silly me. Well, that's my bad for sure. I apologize to everyone for wasting their time.

Assuming that something as radical as replacing the battery with a new one might not fix your computer problem, you just might try swapping the sensor with your other bike, seeing as how you have an identical setup.

I've got the simple 2 step solution to your problem:
1. Remove cycloputer from bicycle. Apply large hammer to cycloputer.
2. Install new cycloputer.

It sounds like your 'puter has developed the dreaded Digital Alzheimer's Disease, the only cure for which I just described. One Hail Mary you might try first is cleaning the contacts on the back of the 'puter--a couple of quick swipes with 600 grit sandpaper should do it. Couldn't hurt to hit the ones on the mount as well, although since your other one worked fine that pretty much eliminates those. My Blackburn has a problem with moisture uptake into the mount when it's foggy out, which causes display errors similar to what you're describing. They stop as soon as I pull the 'puter and dry the contacts.

I've got the simple 2 step solution to your problem:
1. Remove cycloputer from bicycle. Apply large hammer to cycloputer.
2. Install new cycloputer.

It sounds like your 'puter has developed the dreaded Digital Alzheimer's Disease, the only cure for which I just described. One Hail Mary you might try first is cleaning the contacts on the back of the 'puter--a couple of quick swipes with 600 grit sandpaper should do it. Couldn't hurt to hit the ones on the mount as well, although since your other one worked fine that pretty much eliminates those. My Blackburn has a problem with moisture uptake into the mount when it's foggy out, which causes display errors similar to what you're describing. They stop as soon as I pull the 'puter and dry the contacts.



I thought of this, and hence cleaned the contacts on the cradle and the cyclecomp. And then removed and reinserted the cyclecomp dozens of times, but that never helped one bit.


Regarding the Alzheimer joke: it strikes too close to home. I know you meant it in good spirit, but it just doesn't work for me that way these days.

You need this.
http://img458.imageshack.us/img458/8863/exbx0.jpg

You need this.

Thank you for that, I can always use a good laaff...

Hey, this gives me a new idea; the reason why my cyclecomp shows double speed is... because I AM going at double the speed! Maybe I am possessed by the prince of darkness, giving me supernatural strength!

Regarding the Alzheimer joke: it strikes too close to home. I know you meant it in good spirit, but it just doesn't work for me that way these days.

Sorry, my bad....