Knock-Knock Gumball Machine

In this Instructable I am going to teach you how to make a Knock-Knock Gumball Machine. It isn't too complicated, but there are quite a bit of parts and the programming can get very complicated very quickly. The original instructions on the Make Magazine were not that clear and in the pictures it was very hard to see exactly what was going on. Unfortunately, I wasn't taking pictures as I went along with building the gumball machine or wiring up the Arduino, but I promise to give you better pictures of what some of the parts look like. Below is a list of parts you will need and how much you will need to make the gumball machine.

Plywood1/4" thick, or 3/16 " clear acrylic, 2' x 4': 1

Wood stock, 1/2" square, 64" long: 1

Clear plastic light globe, 8" diameter w/ 4" opening: 1

Wood screws: #8 3/4" long (100 screws): 1

Wood Screws: #12 1-1/4 (5/4)" long (25 screws): 1

T-nut, 3/8": 1

Bolt, 3/8", 1-1/4 (5/4)" long: 1

Washers, 3/4" OD, 3/16" ID5Brass tube, 7/32" diameter, at least 2" long: 1

Arduino Uno microcontroller: 1

Servomotor, small, high-torque: 1

Male breakaway headers, 40x1 pin: 1

Perf board, 0.10" pitch, at least 15x20 holes: 1

LEDs, 5.5mm: red: 1

LEDs, 5.5mm: green: 1

LED holders, panel mount: 2

Piezo buzzer, 1" diameter: 1

Resistors 100Ω: 2

Resistors 150Ω: 2

Resistors 10kΩ: 1

Resistors 470KΩ: 1

SPST momentary push-button, panel mount: 1

Potentiometer, 10kΩ linear trim: 1

Power jack, 5mm x 2.1mm coaxial (size M), panel mount: 1

9V DC power supply w/ 5mm x 2.1mm center-positive plug: 1

Insulated solid-core wire, 22 gauge, multiple colors, around 8' total length: 1

Stick-on rubber feet: 8

Small cable ties: 8

Wood screws, round head, #2, 1/2" long: 6

Machine screws, round head, #4-40, 1/2" long: 2

Nuts, #4-40: 2

The first step to making the gumball machine is to get the templates of each piece of the gumball machine. The link below is to each piece that is needed in the making of the gumball machine. It has the dimensions that you need, so if you make each piece by manually cutting with a wood saw, then you can do that. It is much easier to laser cut the pieces, so I will also be attaching the fusion files of each piece for if you have access to a laser cutter. Make sure, before you make the gumball machine out of wood, that you make it out of cardboard so you can see if everything fits correctly and you don't need to change anything. It may make the whole process longer and give you more work, but it is mandatory so you complete the gumball machine without having to restart late into project. Also, just in case you did want to laser cut the parts, I have attached the Fusion 360 files under the template so that you can laser cut/3D print anything you need. The number in the parenthesis next to the name of the part is the amount of pieces you need (Ex: Side (2) means you need 2 side pieces). Another thing, if you get lost or confused or anything like that, under the link to the templates is the link to the original instructions in Make Magazine 25 on page 92.

https://cdn.makezine.com/make/25/secret_knock_gumball_plans.pdf

http://www.blog.neutrino.es/book/Make%20Magazine%20-%2025%20-%20Join%20the%20Arduino%20revolution.pdf

Now that you have all of your parts made out of cardboard, you should put it together using tape or glue. First, tape the two sides to the bottom panel. Then, tape the back panel to the sides and bottom. After this, attach the front panel to the bottom and side panels so you kind of have a base of the gumball machine. Next, you're going to make the gumball funnel, which means you will need to attach the top and bottom rails to each funnel piece. After that, attach the funnel side pieces to the funnel ends and be sure to put the rails on the outside of the funnel. Then, once you put the funnel together, attach the funnel to the top plate. For this next part, I would suggest you find a 3D printer because it makes building the dispensing wheel a lot easier. If you have a 3D printer: Follow the same dimensions in the template, but instead make the thickness about 15 mm, then make a 1" deep hole along the round part of the dispensing wheel. Once you print this, make sure that a 1" gumball fits in the whole. If you don't have a 3D printer: You will need to cut 5 of the dispensing wheel center pieces and sandwich them together. Then, you are going to need to put one stir plate on each side, rotated at about 30° from the center pieces. After this, you will need to drill a 1" deep hole along the round part of the dispensing wheel using a Forstner bit. Drilling will be much harder to do on the cardboard, so just do the best you can. Then, attach the dispensing wheel right and left side to the dispensing wheel rails. These rails go in the bottom corners so they can stabilize the wheel when it rotates. I put three in mine to make sure that the dispenser doesn't fall apart. After you attach the rails to the sides, put the wheel in between with the right and left dispensing wheel side on their respective sides. The right side will have a rectangular hole which is for the servo motor. You don not need to worry about this right now. The last thing to make is the gumball tray. I 3D printed the gumball machine, so I'm not really sure how to make it out of wood. I left all of the Fusion 360 models in the previous Step, so if you want to print it then you have the dimensions that I used (I ended up taking an inch off of the tray part, so just take an inch off the tray if you are printing). Now that you have made all the parts out of cardboard, you can finish your prototype. You just have to make sure the dispensing wheel fits when you put the knock plate (goes on tip of the front panel and smaller part of the side panels) and access panel (goes in front of the side panels and just behind the knock plate). After this, you just have to tape the top on top and you are done with your prototype.

Now that you have finished your prototype, you are going to start the programming portion of the project. For my project, instead of soldering, I used an Arduino and breadboard to wire everything together. This schematic up above was the best thing I found to use for the wiring of the gumball machine. It was pretty confusing at the beginning, but if you take it step by step, it makes everything much easier. For every time you see a line on the schematic diagram come out from a number (or a letter and number; Ex: A0), you want to put a wire in the hole that corresponds to that number (or a letter and number). You can ignore the two white LEDs unless you are making it out of acrylic. After you put the wire in the hole corresponding to the numbers (or letter and number), put it anywhere you want on one side of the breadboard (except the wire coming out of number 7). After you put the wire on one of the sides, then you are going to use the resistor that the schematic says to use (except for wires coming out of holes A1). After this, you are going to plug one end of a wire into the 5V hole and the other end into the long strip on the breadboard that has a + at the top (plug it in high up so that you can plug other wires into the same column when needed). Then, plug another wire into the GND hole and put the other side in the column with a - on top. Now you will have to follow the schematic diagram and my wiring to finish your wiring. Some things I had trouble with are the piezo and the potentiometer. You just need the potentiometer for the beginning to turn the blinking light down. After that you don't really need it, which is why I took it out. The piezo is very sensitive and very important. If you strip the wire poorly or wrong the green light won't work. It will continuously blink and the knocks just won't work at all. This took me weeks and even months to figure out. Make sure it's in very good condition and is able to plug into the breadboard. The final step is to get the USB that is compatible with the Arduino and download the Arduino Uno Software. After you download the software, copy the code provided to you by the link below (just copy and paste onto the Arduino Uno Software).

https://cdn.makezine.com/make/25/secret_knock_gumball_machine.pde

Now that you have the programming working and the prototype made, you are good to start making it out of wood. Pretty much just follow the same steps as for making the prototype out of cardboard. This time instead of using tape you're going to want to use hot glue and/or wood screws. There are some instances that will require you use screws, for these instances you will use a rail similar to the ones that I used on the dispensing wheel sides. They should be a maximum of about 1/2" x 1/2". This is so you can drill the top and knock plate down so they don't move. You are going to glue the rails like they are shown above. After you use wood glue and glue them on, let it dry and you will be all good for drilling. If needed, make any adjustments. In mine, I had to add a couple pieces of cardboard so that wheel dispensed the gumball high enough and it wouldn't fall out in the machine. Another thing I had to adjust was cutting male to male wires or using male to female wires so that I was able to extend the LEDs and piezo to get them in their respective place.

That's it. I hope you enjoyed the Instructable and I hope it didn't take you nearly as long as it took me. I also hope you enjoyed making the gumball machine and that it works to perfection so you can show it off to everyone. The video above is more or less how it should have turned out.