Simple bike computer tutorial

Posted on Feb 7, 2014

The PCB we have made is big and has plenty of space for cutting and adding other bits and pieces. But if we want the final satisfaction of seeing it working, mounting the lot on a real bike, it is a bit too big. Way back in chapter one, we discussed sensors and I recommended we should stay with the herd and use some sort of hall device. Well now w

Simple bike computer tutorial
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e physically need one to get our hands on. I realise that it is almost impossible to buy a potted sensor +cable as a spare, they all come with a bike computer. Now we could buy a complete bike computer kit and throw the computer away. Or keep it for later as a spare. So we have results similar to the diagram. Similar means there is a measurable resistance change when the magnet is passed over and CLOSE to, he sensor body. How can we check I connected my multimeter on the mA scale across the end of the sensor wire in the handle bar mount shoe ( place where it enters the computer). The reading is of course zero mA. Next I took one of those little kitchen fridge magnets and waved it very close ( 1mm) to the Unknown type ” of sensor. I had to find the best direction to move the magnet over the sensor, but eventually I got a reading of a about 50 uA Well I cheated as I knew it was a coil sensor, but if it hadn`t been a coil sensor, instead some sort of HALL device, then we would have no change at all when the magnet was passed across the sensor body. In that case we would need to condition the pulse output. For those interested, basically a limiting amplifier to ensure that even at the slowest speeds there is enough signal for the PIC to detect at the PORTB input. But this could be tricky, without an oscilloscope, so unless you really have set your heart on making it work, best look for a HALL device type sensor. No panic about...

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