Coin Dispenser 2024

Introduction: Using the SparkFun Inventors Kit for Arduino Uno our group created a coin dispenser. Using these instructions, you should be able to build and code a coin dispenser. The dispenser can dispense a variety of U.S coins (up to ten of each) based on a user's input. This project can compete in the 4H robotics competition.  

1. 1 SparkFun Inventors Kit 
2. Breadboard 
3. Ardunio Uno 
4. Jumper Wires 
5. 16x2 White-on-Black LCD 
6. 10k Trimpot 
7. 4 buttons 
8. 1 resistor 
9. 1 extra button 
10. 1 extra pack of wires
11. 3 extra servo motors  
12. 4 AA batteries 
13. Cardboard 
14. Thicker Paper of your choice (construction, cardstock, notecards) 
15. Hot Glue Gun 
16. Electric Tape

Link to the sparkfun kit that contains most of the supplies listed above: https://www.sparkfun.com/products/15631  

Cut out four pieces of cardboard that are 3 inches tall and coin diameter wide (the general idea is to create a box where only one coin can sit on the bottom at a time), see pictures one and two. Then hot glue them together to form a rectangular prism as shown in pictures three and four. Repeat this process three more times so that you have four complete boxes when finished.

Using your cardboard, cut out four rectangles that are 2.5 inches tall by 1 inch wide (see picture one), these will be piece one. Next, cut out a shape like the one in picture two that is 4 inches wide at the bottom and 5 inches tall at the tallest point (keep the shorter sides about 4.5 inches tall). This will be piece two; repeat the previous step to make four of these total. Using picture four as a reference, hot glue the side of piece two to the middle of piece one. Once that has dried hot glue the coin holder (picture three) from the previous step to the side of piece one and bottom of piece two. Tip: Feel free to label the pieces physically to make assembly easier!

Next cut out a section of the cardboard in piece two from the previous step. Next cut out a piece of cardboard about 1 inch tall and 0.5 inches wide and attach it to piece two (next to piece one as seen in the images above) using hot glue. Next create a square about 2 by 2 inches using a thinner material than cardboard (we used the carboard from soda boxes). You will then hot glue your servo motor to this 2x2 piece so that when the servo motor spins the cardboard can knock the coins out of the slot. Beneath this piece will be another piece of cardboard that has a cutout for the servo motor, you will then hot glue the servo motor into this cutout as seen in the third image. Essentially you are creating a sandwich of cardboard in which the coins and servo motor sit so that when the servo motor moves it slides the coins out of the slot so they drop down into the container you will build later. Repeat this process for all four Coin Dispenser mechanisms. We included several photos above and we recommend looking at them as a reference. (There are also additional photos included that show the servo motor glued to the cardboard piece before the entire mechanism is put together. You may find these helpful to look at by clicking on see more images).

Next we created the box that holds the coin dispensing mechanisms. This box is 15x15x15 inches big so each piece of cardboard you used to make it will by 15x15 inches in size. The back piece and the two sides will be regular 15x15 pieces of cardboard. The front piece is where the lcd and buttons will be attached. Using the first two images as a reference you will need to cut out a rectangle for the lcd screen to fit in and then five squares below that, evenly spaced, for the buttons to fit in. At the bottom of this front piece include a cut out for a tray to slide into. You will then hot glue all four of these pieces together to create the outer sides of your box. Once you have finished that,

Begin by using hot glue to attach your bread board and Arduino to the box (make sure that your Arduino is fully screwed into the black stand that comes in the sparkfun kit, as well as your breadboard being stuck down securely). Before gluing it down make sure that it is close enough to your lcd cut out that you can then fit the screen into the hole (as seen in the image above). Next you will add the buttons so that they fit through the cutouts with the button for the quarters on the far left and decreasing coin values as you move to the right. The final button on the right should be the button that dispenses the coins.

In this step you will create the tray that the coins fall into, this tray will be a continuous piece that is connected to part of the slide that the coins will move down to end up into the tray. The image above will likely be the most help when it comes to the shape of this piece, but you will need the tray to be the same width as the rectangle you cut out earlier. On the tray par at the bottom create two flaps on the sides that can be folded up to create the walls. Then on the back side of the tray you will be creating a shape that funnels inward as it gets closer to the tray. Next you will cut out a piece of cardboard to be the front wall of the tray. Finally, hot glue all of the walls together at the edges to form the walls of your tray.

Taking the piece from the last step slide it under your box so that the tray sticks out the front of the rectangular hole at the bottom of the box. Then hot glue the end of the funnel to the back half of your box the create a slide that the coins can move down. Next add a 15x15 inch piece of cardboard to the bottom of the box to serve as your floor using hot glue. You will then create two triangular pieces and two rectangular pieces the length of the box. The triangular pieces will be hot glued vertically along the initial slide piece to create a level surface to glue the rectangular pieces to. Once the triangular pieces are glued down attach the rectangular pieces at an angle as shown in the photo so that the side attached to the box is higher up than the side attached to the triangular pieces, this will allow the coins to slide down the rectangular pieces and onto the slide when they are dispensed.

Using the image from above you will then attach all four of the coin dispenser mechanisms that were finished in step three onto the sides of the box. You will hot glue the side of the mechanism that contains the servo motor to the wall of the box, keeping the side that contains the coins on the inside of the box as much as possible. (Tip: Make sure that the cardboard on the servo motor can fully rotate to push the coins out without hitting the wall before you hot glue it down to the wall or it will be much harder to fix after the fact). Attach two coin mechanisms on each wall of the box, making sure that the wires for the servo motors can still reach the breadboard attached to the front wall.

Again using the photo from step eight, you will attach a battery setup to the Arduino board in order to power the coin dispenser. We wrapped ours in electrical tape thoroughly and then used hot glue to attach it to the top right side on the inside of the front wall of the box. Alternatively you can skip attaching the battery pack and just connect the Arduino to a computer.

Lastly, you will create the lid of the box using a 15x15 piece of cardboard (DO NOT fully glue this piece down or you will be unable to refill your coin holders. You can also decorate your box however you like, our group chose to decorate it with Christmas wrapping paper and add a message that says Happy Holidays when dispensing the coins (you can edit the code to add a different message of your choosing if you would like).

Creating this project in TinkerCad first may help you make sure you have properly wired and set up your arduino and breadboard before recreating it using your sparkfun kit.

Link to an explanation of the wiring in the TinkerCad image above:

Link to the code needed for the project:

ME 208 Coin Dispenser Project.docx

Here we included a link to a video detailing the building process step-by-step.

ME 208 Coin Dispenser Construction Guide

We also included a video where we demonstrated the prototype we made of this device.