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There are for sure more methods how to count wheel pulses on a motorbike front wheel and everybody should decide himself what the best and cheapest solution is. We received many e-mails with good designs and would like to thank all motorbike enthusiasts on this way for their input.
In our example and on our machine the
pulse counting is done with the help of a Reed relay. The possibility to design that with the help of a hall sensor could be even more reliable, since no mechanical contact is used. Nevertheless, when we
did this project, I’ve found a BC700 bicycle speedometer reed relay in my accessories box, so we used that.
The reed relay contact is switched by
the magnet installed at the brake disk. These magnets can be purchased at nearly any motorcycle accessories shop or in bicycle stores, since they are used with the bicycle speedometers that are available
on the market. We use a special version that is supplied for the brake disk. The two NAND gates in the
7400 chip buffer the pulse, that is then divided by 16 with the help of the 4024 chip. The counter 74193 counts up. That’s it.
The Conrad Electronics C-control
microcontroller then reads the outputs Qa - Qd and resets the counter after the read cycle on the Clr input. Then the counter starts from zero again. This small buffer circuit is necessary since the
C-control is unfortunately not a real time processing system. The program that runs on the microcontroller reads the input, processes the result and performs several other tasks until it passes by the
loop to read the input again. If the design would have been setup that way, that the microcontroller would have to read the input signal directly, then the maximum speed you would have been able to drive
with the motorbkie would have been 30km/h. Otherwise the system would have lost counts, since this microcontroller is not the fastest one. Using the buffer circuit as we do, allow max. speeds beyond
300km/h easily.
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