Lately, I've heard a lot of junk. Due to our consumerist lifestyle, we discarded equipment in good working condition to buy the latest release. Thus, we contribute more to the growth of this garbage. My intention was to recycle this type of material and inspire others to do the same.

Materials needed:

- A reader of CD's

- A piece of cardboard 15X30 cm

- An old cd

- Reedswitch a normally open (magnetic drive key easily found in electronics stores)

- A calculator

- 2 screws with washers and nuts (optional)

- Wires

- Glue

- Hot glue

- A rubber band to hold money

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Step 1: Separating Material

Open the reader, highlighting the optics, the engine that runs the cd and the amount of metal is in above the engine, setting the album to him. At the optics, remove the two magnets. Be careful because these two magnets are very strong and can unite, injuring the fingers or hand.

The cardboard was cut into three strips of 25 x 5 cm.

The reed switch was stuck on a small piece of cardboard, the edges with hot glue to be handled because it is very fragile.

Open the calculator and connect a wire to connect each of the SAME button and set aside.

I soldered the wires on a jumper and I fixed it so that no contact from the outside. This way when not in use, simply unplug the wires.

Step 2: Mounting

- Glue the magnets at the ends of the CD so that they are 180 ° from each other

- Paste the strips of cardboard.

- Solder the wires on the Reed Switch

- Determine the amount of cardboard in the engine using two screws with nuts and washers.

- With the help of hot glue, glue the reed switch in the engine mount so that the magnets pass in front of him.

- Plug the wire into the calculator and set it on cardboard with the help of the elastic. Hold the excess wire in the rubber band.

- Program the calculator.

Step 3: Operation

The odometer works as follows:

Every time I pass by a magnet reed switch, it closes the contacts, functioning exactly like a lamp switch. But it just gets closed while the magnet exerting force on it.

By close contact, like the calculator button is triggered, adding the number of turns and thus calculating the distance traveled.

memory calculation:

L / 2 = [2 * pi * r (in meters)] / 2

L / 2 = length of circumference divided by two (because there are two magnets)

pi = 3.1416

r = 3.5 cm = 0.035 meters (radius from the center of the CD to the magnet)

L / 2 = 0.11

The Software is as follows:

0,11 +

Then, just run. Each time the magnet passes the sensor, it should be counted 0.11 m

Note: The more we put magnets, the greater the precision of it. Take care to space them at the same distance from each other. But we should divide the length of the circumference by the number of magnets placed. One should also take care not to turn very slowly because the CD I found that when passing slowly through the sensor, it closes twice, causing a misreading. To minimize the chances of this happening, simply run faster or stick the sensor in the vertical.

Hope you enjoy. Comments are always welcome.

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    9 Discussions


    4 years ago

    Where do you find a reader of CDs ?

    Husham Samir

    6 years ago on Introduction

    Very Nice !!!
    I made similar project when I was in college but I use optical coupler as shown in web site below

    1 reply

    The optical coupler is a cheap and effective solution. However, I decided to use materials I had at home. And the reed switch very well attended. I like your project. Good job.


    Great idea! Although I would suggest rewording a few of the steps as i got confused about how to wire the calculator

    1 reply

    Hello in the calculator, the button "equal" has two contacts like a key open. It is simply solder two wires in such contacts.


    8 years ago on Introduction

    I was working on the same thing for the transform it contest by a shaft encoder from an old mouse and a PIC microcontroller, but you did it first, good luck.

    1 reply

    8 years ago on Introduction

    The basic idea is quite neat, although I would likely make a few modifications if i built one. Ex... more magnets( more precision), rubber rimmed wheel(reduce slipage), and i might go all out and do some microcontroller action but that overkill.

    1 reply

    Reply 8 years ago on Introduction

    Good idea. I thought the same. But the main idea was to make somethig easy to make and faster. thanks to share your idea