In this instructable I am going to explain how to make a bicycle speedometer, in fact I have an old exercise bicycle which its mechanical speedometer was broken a long time ago, and I decided to replace it with an electronic one, but since there are many speedometers reported in instructables and I had no idea which one gave the right result, I decided to make a test rig in which I use a motor gearbox with known RPM(50 RPM) to test the speedometers with different Arduino sketches to see which one gives a better result, furthermore in most of these instructables there was additional components in the circuit, like LEDs and I just needed a dedicated speedometer and odometer, so I had to change those sketches to find the best sketch which was suited to my simple case and my available components, the role of the test rig was also a kind of simulation or emulation and the fact that first be sure the system works well then to assemble it in to a desired container or case, so please read the rest of this report to see how I made a speedometer.
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Step 1: Bill of Materials
Materials and components which are used in this project are as follows:
1- A cream container
2- Two small pieces of perf. board
3- One reed switch
4- Two female jacks
5- One rocking switch
6- One Arduino pro mini
7- Two pieces of female headers
8- A 1.5 k Ohm resistor
9- A 16*2 LCD
10- Three batteries of 18650 Rechargeable Lithium Batteries, salvaged from thrown away laptop battery packs
11- Enough 10 centimeter pieces of bread board wires
12- A push button
13- A 10 k Ohm potentiameter
14- A small piece of electrical duct, say 10 centimeters
15- One and half meters of wire
16- a piece of small magnet
Step 2: Tools Needed
1- Arduino UNO to program Arduino pro mini
2- A geared motor with speed of 50 RPM with appropriate couplings
3- A plastic reel or a circular plastic with known diameter
4- Some pieces of wood to build the test stand of the project
5- Soldering iron and solder
6- Small drill
7- Crocodile clips and attached wires
8- Super glue
9- Power supply
10- Enough bread board wires
11- A multimeter
12- Wire stripper
13- Small and medium size screw drivers
14- Small screws
15- bread board
Step 3: How to Make
First of all making it is easy you can just use the Arduino sketch and an Arduino UNO to program the pro mini, and then by using bread board and following the electronic sketch- Fritzing- to connect all components including Arduino pro mini, LCD , resistor, potentiameter, and reed switch by using bread board wires. after making that and assembling the test rig according to the photos, you can test the circuit, you should insert the perimeter of the test wheel in the program in this case o.52 m, then by multiplying the 50 rpm by the perimeter and converting to km/h check the value with the value that the LCD is displaying. After some adjustments and become sure about the correctness of the circuit and program, the container should be prepared and an opening with the same dimensions of LCD made on the container cap and making the holes for potentiameter and push button - which is already connected to a small piece of perf. board and screw this piece to the container's body, then use female headers for earth and +5 V headers to a piece of perf. board and connecting the 1.5 k Ohm resistor to the ground, then inserting the LCD in to the opening of the cap and inserting batteries- which three of them are packed together in a series connection- , Arduino and other component except the reed switch, and connecting two female jacks and a rocker switch on the casing body then the system would be ready for the final test, after using the test rig for the last time and being sure of every thing, we can insert the perimeter of the exercise bicycle which is 0.82 meters in my case the system is ready to be connected to the bicycle in which reed switch and a magnet is attached to its turning wheel and the pillar, now everything is ready to start exercising and enjoying your speedometer.
Hope you've liked this project.