Using an Arduino, it is easy to make a speedometer/tachometer for virtually any man-powered vehicle. I made one for my skateboard that used a small magnet to count revolutions and utilized an LCD display screen. This Instructable will show you how you can do the same step by step.
You will need a few things before we get started.
1) A man-powered vehicle (I will be using a skateboard)
2) An Arduino
3) A plastic Arduino protective box (pictured)
4) A small magnet (mine is 1/4 inch in diameter and about 0.2 inches tall)
5) A magnetic relay switch
6) A 9V battery and an adapter that connects this battery to the Arduino plug (pictured above plugged into an Arduino)
7) A small LCD screen (16 x 2 character display)
8) 10K and 47 Ohm resistors
10) A soldering iron and solder
11) Gorilla glue, super glue, crazy glue, or some adhesive of the sort
12) 10K Potentiometer