Counting Bike Wheel Revs

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Been looking all over the web for ideas.... looking for the absolute
cheapest method, in a mass production environment to count the wheel
revolutions of a pedal bike.

Hall sensors are too much....

Would a small coil of wire on PCB and a magnet be the solution?

Any other ingenious cheap methods?

Accuracy does not need to be 100% so the odd missed revolution is fine.....

Thanks!
Rick.



Re: Counting Bike Wheel Revs
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How about installing a contact pin in a spoke and
a corresponding fixed insulated contact in the
structural tubing nearby, and counting the contact
hits (with bounce suppressed).

--

Tauno Voipio
tauno voipio (at) iki fi



Re: Counting Bike Wheel Revs
This would work, but would not be the cheapest and requires the user to need
to align things too much... needs to be contactless....

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Re: Counting Bike Wheel Revs
snipped-for-privacy@iki.fi.NOSPAM.invalid says...
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They are?   Hall effect sensors are well under $1 each in the DigiKey
catalog--probably less than $0.60  in large quantities.   If you pick
another solution, you could use up that much in signal conditioning
and PC boards pretty quickly.
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OTOH,  you could fasten a playing card so that it hits the spokes.
Add a microphone, amplifier, and DSP chip, and you should be able
to determine wheel speed pretty accurately!  ;-)  The sound effects
should be a good marketing point!



Mark Borgerson



Re: Counting Bike Wheel Revs

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There are two such sensors in each mechanical mouse.  Can't be more
than $1 each.  You just need to make the transfer gears and mounting
stuffs.  You can always buy up all the used mouses for the sensors.

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Re: Counting Bike Wheel Revs

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My Sigma Sport 600 bike speedometer, odometer and trip calculator wa quite
innexpensive as a complete system (approx UKP12.00) and uses a magnet on
the spokes and a reed switch in the fork mounted sensor. A magnet and a
coil would probably do as well.

--
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Re: Counting Bike Wheel Revs
Have you seen the reed switch, I was under the impression it was a hall
sensor most of them....

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Re: Counting Bike Wheel Revs

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No, but I've heard them.

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Perhaps some of the newer ones are using hall-effect sensors,
but I'm pretty sure that a few (e.g. 10) years back they were
pretty much all reed switches.  If you held the sensor close to
your ear and moved the magnet past it, you could year a faint
clicking.

In my experience, hall-effect sensors don't produce much signal
and are rather fussy to interface to.  They require a analog
amplifier and either a comparity or A/D converter.  The output
signals aren't very consistent from one unit to the next.

A reed-switch OTOH, is dead simple to interface to.  All you
need is an input port pin (or IRQ pin) and a pullup resistor.

--
Grant Edwards                   grante             Yow!  Let's send the
                                  at               Russians defective
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Re: Counting Bike Wheel Revs
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They have these things now called "Integrated Circuits"!!  ;-)
The $1 sensors in the DigiKey catalog include a signal conditioning
chip that converts the magnetic signal to a digital output.  Three
pins:  Power, Ground, digital output.
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True. But does it have the same sensitivity, a built-in schmidt
trigger and other features (about which I know little)?

Reed switches are about $0.39 qty 1000 in the Jameco catalog,
but you still need to mount it, make sure it is
oriented properly, and protect it from breakage.  A 3-Pin
SIP Hall sensor might be worth the extra $0.60.

I've used reed switches, but never on the fork of a bicycle,
where shock and vibration might be an issue.  Are those issues
in favor of a Hall sensor?


Mark Borgerson




Mark Borgerson


Re: Counting Bike Wheel Revs

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Darn.  What will they think of next!  Someday I bet they put a
whole computer in one package...

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I would think that either would work fine.

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I don't remember bicycle computers ever having any problems
with them.

--
Grant Edwards                   grante             Yow!  Where does it go when
                                  at               you flush?
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Re: Counting Bike Wheel Revs

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   A reed switch doesn "Schmidtt triggering" naturally, though there
may be a slight problem with contact bounce, that a Hall effect sensor
won't have.

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   Don't you also need to mount a Hall effect sensor, make sure it is
oriented properly, and protect it from breakage? Okay, it's not glass
like a reed switch, but it still needs to be 'adjusted' in relation to
the magnet on the wheel, just as does the reed switch.

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   Reed switches also have the advantage of being totally passive and
not needing power. An integrated-circuit Hall sensor probably takes
(just a swag, I haven't looked at a data sheet lately) 100 or 1,000
times as much power as the average electronic bicycle
speedometer/computer.

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-----
http://www.mindspring.com/~benbradley

Re: Counting Bike Wheel Revs
ben_nospam_ snipped-for-privacy@frontiernet.net says...
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The hall-effect sensors need about 5-10mA.  Depending on the display,
that may be just about as much as the rest of the computer.  A reed
switch with a 10K pullup would certainly be less, though.

Mark Borgerson


Re: Counting Bike Wheel Revs
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Yes it does.  

According to the reed switch data sheets I've seen they do have
hysteresis: the field strength required to close an open switch
is higher than the field strength at which a closed switch
opens.

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True.  Though that's easily ignored by a few lines of code
(assuming it's being interfaced to a uC).

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If the previous guess of several mA for a hall effect sensor is
true, that a lot of current.  I don't know about other bicycle
computers, but a button battery lasts for years in mine (well,
I don't ride a lot so that's not much of a datapoint).

--
Grant Edwards                   grante             Yow!  I KAISER ROLL?! What
                                  at               good is a Kaiser Roll
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Re: Counting Bike Wheel Revs

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Well, you could take a look at how it's done in other absolute
cheapest mass-production products.

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Doubt it.  You'd need some amplifier/filter/interface circuitry
to sense the current induced by the magnet -- probably about
the same price as a hall effect sensor.

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Go the a local bike shop, buy a few computers (cheap ones
aren't much more than 25USD), and take apart the sensors.

I think a magnet on a spoke and a reed switch attached to the
frame is the standard solution.

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                                  at               GAME I want to know your
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Re: Counting Bike Wheel Revs
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That would fail at low speeds, and so probably fail the user
'walk the bike to check' test...

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You don't say what other resource you have ?
Viz: A smarter processor, can often use a dumber sensor.

REEDs have been suggested, and they have a key advantage of
being nominally sealed/waterproof, and have a high KISS rating.

Asian Detect switches are cheaper, but fail the splash proof test.

Do you need to know actual revolutions, or is speed of more interest ?
Would a one-per-spoke signal, give better display results, than
one-per-rev ?

For one per spoke, your choices are optical beam [needs dual cables, one
per fork] and magentic proximity sensing [needs ferrous metal spokes]

-jg


Re: Counting Bike Wheel Revs
Yeah more like one per rev is fine.... I think it looks like magnet and reed
switch testing right now....

VERY KISS!


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Re: Counting Bike Wheel Revs
On Monday, in article

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Attach a wider reflective or even non-reflective item to one spoke and
have a opto sensor attached to one of the forks that detects a longer
pulse (either darker or lighter pulse) than the spokes.

Could even be an infra red led on other side and covers to obscure as
much sunlight a possible. Thus also be useable at night.

Could be placed nearer axle to reduce dirt/mud issues.

--
Paul Carpenter          | snipped-for-privacy@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/ PC Services
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Re: Counting Bike Wheel Revs
Thanks guys! Looks like it will be magnet and reed switch testing right now
as this whole thing I want to make needs to come in around $1.50 to be
feasible!

Let ya know when its done!

Rick.

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Either a magnetic reed switch or count the spokes with an
opto-interrupter. I suspect that the cost of the amp for spoke counting
would offset the cost gains over a cheap Hall sensor though.

Bob

Re: Counting Bike Wheel Revs

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Did anyone suggest a conductive metal flag projecting from the side of the
wheel (or both sides uf balance is critical).  It could close a contact
(soft and/or flexible) and make like a momentary switch.  If there is a
micro involved it could even detect missed hits based on timing.
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(Please pardon any typos.  I am typibg one handed for a while due to recent
hand surgery)

--
Scott



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