Student Turns His Locker Into A Soda Vending Machine

Back in high school, on my summer breaks, ambition was at the bottom of my list. I wanted to hang out with my buddies and do as little as possible. It would never have occurred to me to take on a project. Turns out I could have been doing something cool and setting myself up for the future at the same time. C'est la vie, amirite? 

Instructables user Mistablik had a different idea for how to use his summer break. Headed into his senior year, he wanted to build a soda vending machine for his locker at school. The project would challenge his mechanical engineering and programming skills and take months of planning and building, but in the end he had a unique locker and he was the talk of the school.  

After consulting with some friends about his crazy scheme, Mistablik got down to work, starting with the control panel. He bought an Arduino, coin acceptor, an LCD screen, and a magnetic reed switch, and powered it all with a 21-volt battery.

He figured out how to program it to accept nickles, dimes, and quarters, and to dispense two kinds of soda selected with arcade buttons. 

To make the face of the control panel, Mistablik turned to the school's laser engraver. 

After figuring out where everything would fit behind it, he mocked up his control panel in Photoshop and CorelDRAW, cut some holes for the screen, buttons, keyhole, coin slot, and displays, then put the laser engraver to work on his simple, classic grid design on black acrylic. 

Of course, the control panel wouldn't be complete without some anti-theft measures.

Mistablik cut two boards of the same thickness as the lip that the locker's door rests in, then put a couple of holes in them where a key-driven arm could slide in.  

With the control panel complete, Mistablik made an acrylic box to encase it so it would sit neatly on the lunch box shelf inside the locker.

It holds the battery and the change drawer, and he built in a power switch to turn it off when the locker is closed and a charge switch so he could charge the battery without having to open the whole machine up.

However, when he had all that done, he realized people might be able to cheat his machine...

As it turns out, the way Mistablik had programmed his coin acceptor meant that static electricity could trick the machine into thinking a nickle had been deposited. 

He could have fixed the problem by grounding his control panel, but he didn't want to alter the locker in any way. So he needed a programming solution – changing the number of pulses each coin sent to the coin acceptor meant that one static shock wouldn't be enough to make the machine think a nickle had been put in.

It's hard to believe how much work he had put in before even getting to the can dispenser. 

But of course no vending machine would be complete without it! Mistablik designed the dispenser boxes on Autodesk Inventor before laser cutting the pieces and assembling them with wood glue. Each box holds six cans and has a hole on the side where the single-can dispenser would be mounted.

The C-shaped can dispenser took some trial and error to design and build.

To keep it low-profile, he used a 1:1 gearing ratio and mounted the servo inside the box. 

To this point, almost everything had been done outside the locker. It was time to get the dispenser boxes inside.

He had to put the boxes in one at a time to get them to fit, but they did!

But just getting the parts into the locker doesn't make a vending machine...

The dispenser boxes would work, but they didn't exactly look the part, so Mistablik had to laser-cut another panel to keep with the theme he had started with the control panel.

And of course there's a hole at the bottom just big enough to grab your soda. After a test run, he also decided to put in an extra piece of acrylic at the bottom so the cans didn't come crashing down onto a metal floor.

Good planning kept room between the control panel and the dispenser boxes for some storage space, again accessible with a key.

And, once again, fronted with laser-cut grid-patterned black acrylic.

With the bottom half of the machine more or less done, Mistablik had to consider more anti-theft measures.

He didn't want anybody walking off with all of his hard work, so he cut a few lengths of MDF to act as spacers and jams that would keep everything in place and allow the door to close smoothly.

Mistablik considered taking out the backpack hook for cord management, but again, he didn't want to alter the locker in any way.

Fortunately, there were already two holes in the back of the locker he could run the cables through. 

He's almost done – time for some finishing touches!

Because he had set up the soda machine to turn off when the locker was closed, Mistablik didn't want the door being left open by people buying a soda.

So he installed a 15-inch tension spring to keep it closed and again fortune smiled on him – there were already a couple of conveniently placed points in the locker where he could mount the spring without having to drill his own.

Although he didn't want the door staying open, it wouldn't be good for business if the door locked every time it closed, so Mistablik had to jam it open.

After putting in the combination once and holding the latch open, he jammed the lock with a pencil and taped it in place. The door will latch, but it won't lock.

With everything ready to go, Mistablik prepared a surprise for his first soda sold: a prom invite for his girlfriend.

Talk about smooth!

"After day one, the vending machine was a hit!" he wrote. "On average, 6 cans are sold in just one passing period."

"Although to me, it was far more rewarding to hear "Dude, have you checked out locker 808 yet?" as students passed each other in the hallway."

Check out his full project instructions on Instructables – including some of his code!