When you are displaying your speed in digital lcd screen you can just show any speed in there, just write the number and it is, but with an analog speedometer you are physically limited by the size or your scale.

In the code you will find a variable called maxSpeed, this number represent the speed when the needle is at the end of the scale and the display can not show any higher speed. If you go faster than this the led will turn on, meaning that you probably should choose a higher value.

In my case I decided to use 36 km/h, is a speed that I won't usually achieve while riding in the city, and I know that if the needle is in the first mark I am at 9km/h, in the second one at 18 km/h and in the third one at 24 km/h. I didn't include any numbers in my scale so I can change my max speed at any time.

For finishing this project print the scale in the image (of any design of your own), glue it on top and then glue a bright color needle in the axe of the servo.

Last words

I hope you liked this instructable, it is my first project using and arduino.

I am from Argentina and I will be glad if you let me know any grammar mistake you find.

Bruno.