24 Jan 2012

How to Make an Odometer

This is a really interesting calculator hack and this concept can be useful in diverse projects. If you were looking for a means to find out how much you travel on your bike, then this is just the right place. All you need to spare is a dirt cheap calculator and 20 minutes of your free time. 

Materials Required:
  • A calculator
  • A reed switch
  • A powerful magnet (preferably light and small)
  • A couple of wires
  • And a bicycle :P

Tools Required:
  • Soldering iron and solder
  • Double sided tape
  • Duct tape or any strong tape 

Step by step instructions:
Calculator PCB
  • Open up a calculator and locate the equal sign button on the PCB
  • Locate the 2 holes that are linked to this button (tricky)
  • Take 2 wires of lengths depending on the distance from the calculator to the magnet
  • Solder each of the 2 wires to the 2 holes of the equal sign button
  • Twist the other ends of the wires with the legs of the reed switch and solder both the joints
  • Put back the cover of the calculator and switch the device on.
  • Press the '+' button, then  '1' and then bring the magnet back and forth to  the reed switch and the number on the LCD display should keep increasing by one. If you succeed doing this then your odometer is almost complete!
  • Measure the radius of your wheel and calculate its circumference.
  • Now fix the magnet on one of the spokes of your bike close the axle with some tape.
  • Fasten your calculator firmly on your chain guard (or any other flat surface) with the double sided tape
  • Tape the reed switch as close to the magnet as possible yet at a safe distance from the spokes
  • Again switch the calculator on, press the '+' button, insert the 'circumference' of your wheel preferably in meters and RIDE ON!!
Sorry, I couldn't find a cleaner bike!! :P
Every time the magnet comes close enough to the reed switch, the '=' button is shorted and the circumference of your wheel is added to the distance you have traveled. Your bicycle odometer is complete! 

NOTE: At high speeds the reed switch will not always get triggered by the magnet and the odometer might display faulty results. 

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