[dorkbotpdx-blabber] Making a stationary racing machine

Trystan Cobbett trystan.cobbett at rapha.cc
Thu Jun 19 12:05:22 EDT 2008


Hmmm, that could work too, I need the magnetic sensor to read about 6  
feet from the circuit board so I was planning to convert it to Cat 5  
cable. This is how the prototype was built and seemed to work well, I  
think you're right in that a simple enough cyclometer would do the job.

Trystan Cobbett

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On Jun 19, 2008, at 9:04 AM, Paul Stoffregen wrote:

> A few years ago I used one of those little sensors.  It was already  
> installed on the bike.  The trip computer part had long since been  
> removed, but the magnet on the wheel and sensor on the frame were  
> still there.  I had absolutely no information about it.
>
> It had 2 wires, which would short together when the magnet passed  
> under the sensor.  I believe it was a tiny reed relay.  I used a 10K  
> pullup resistor to 3 volts.  It did not matter which polarity I  
> used, and I did try reversing the wires and it worked either way, 3  
> volts without the magnet, almost exactly 0 volts with it.  I did not  
> see ~0.2 volts as a bipolar transistor would have, or something  
> higher like a diode drop.  When shorted, it was almost exactly  
> zero.  It remained a short indefinitely if I held the magnet in  
> place, so I do not believe it was a hall effect or other active  
> sensor, as it was only 2 wires and had no way to get power during  
> that time.
>
>
> -Paul
>
>
>
> Dread Pirate Kermit wrote:
>> On Wed, Jun 18, 2008 at 10:22 PM, dan p <gunterhausfrau at gmail.com>  
>> wrote:
>>
>>> sure, lots.
>>>
>>> a typical bike computer uses a magnet and a "sensor" I believe  
>>> usually a
>>> coil and counts the number of times the magnet passes the coil  
>>> (pulses from
>>> the coil, magnet on the wheel).
>>>
>>
>> I think they typically use a Hall effect sensor, but close enough.
>> Whenever the magnet passes the sensor, a pulse get's sent to the
>> 'brain'. X pulses/sec = Y MPH. Most modern motorcycle spedometers  
>> work
>> almost exactally the same.
>>
>>
>
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