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MONITORING THE REVOLUTIONS

A Pedal Cadence Counter
by Matt Meerian

Start ý The Hardware ý Microcontroller Software ý Desktop Software ý Placement ý Happy Trails ý Sources and PDF

PLACEMENT

The circuit can be mounted just about anywhere on the bike. An easy place for a temporary mount is a wedge-shaped pouch that fits under the seat and is attached by Velcro. For a more permanent mount, the circuit board and battery should be mounted in a small plastic box. The box can be attached to the bike by plastic zip ties found at any local hardware store. Rubberized tape on the bottom of the box makes a nice buffer between the box and the frame of the bike.

The LED should be placed where it is plainly visible, so the rider can see that the circuit is working properly.

I used a piece of a magnet (1ý long, ýý wide, and ýý thick) from an old floppy drive to activate the Hall effect sensor up to ýý inch away. My first attempt at mounting the magnet was a failure. Glue and wire ties do not hold the magnet onto the shank of the pedal. For my second attempt, I used electrical tape, and it worked well.

The shank on my mountain bike is not magnetic. If it were, the Hall effect sensor would have a difficult time being tripped by the magnet. The tricky part was getting the Hall effect sensor close enough to the magnet and still be on a semi-flexible shaft.

The first thing I did was solder three 28-gauge, stranded wires (3ý long) onto the leads of the sensor. I used heat-shrink tubing around the leads to keep them from being shorted together. To keep all the wires and sensor in one package, I used 3ý of ýý heat-shrink tubing over the Hall effect sensor. The heat-shrink tubing also makes mounting the sensor to the bike a little easier.

So, I am left with a Hall effect sensor in the heat-shrink tubing on one end. The other end, 3ý away, has three 28-gauge wires. I used a small plug to attach the three wires to the circuit board.

The Hall effect sensor-magnet combination was actually easier to get working than I anticipated. Except for the first magnet falling off, everything went smoothly.

For testing, I used 3 Ni-Cd batteries wired in series. They generate about 7.5 V and have much more capacity than I need.

Two hours and 8 min. of data logging capability might be limiting for the more serious athlete. For more data logging capacity, an external 8-KB serial EEPROM could be added to store data.

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