The Zap-A-Mole Machine

My interpretation of the whack-a-mole arcade game

(See the full project here!)

With a surprisingly simple premise, i found that this project was deviously hard to construct, from conception to final touches. On top of everything else, this project was a study in miniaturization, mass production from a single design, and consumer/user interface. The whole assembly was constructed from plastic, perf-board, (and part of a coffee can). Interestingly, the primary tool used for this project was a dremel tool - which sufficed perfectly for all the cutting and drilling involved.   The whole project  cost me $14, not counting the arduino- mostly covering the display and its electronics.

Buttons Schematic

Possibly the most important part of the whole zap-amole machine is this humble sheet of paper you see here.  With the arduino i was using, i could only have 12 digital outputs, so after many iterations, i came up with this grid system, which constitutes the core of the zapamole! The grid is basically 16 voltage dividers made up of an LED and a resistor.  By setting the vertical input to 5v, and the horizontal input to 0v (by default, the inputs are reversed so no current will flow through the LEDs), a single LED is lit. Furthermore, when the corresponding button is pressed, a medium voltage is sent to the output.  When the wrong button is pressed, the output voltage is either 5v or 0v. (Ideally, of course). The transistors were added later when i realized sending large currents through the arduino might not be the best idea...

Arudino!

An early test of the arduino I used for this project, except here with a 3x3 matrix. (The Led's are actually all blinking very fast, they looked like a modem here!)

Original Button Design

This is the original design of the button assembly- each column would have its own 'button plate' on which plastic buttons would push on rubber spring contacts, closing a contact on the button plate (just like a calculator). 

In this design LED's would light up the plastic button from the side, through a reflector, ideally scattering light upwards.... As you can see, vertical space is cramped in this design!

Buttons Design

Planning out the buttons before i cut them. (only two columns here, there's actually 4). dimensions of each button are 1.3cm X 1cm, 0.9cm X 0.5cm margin, respectively.  This sheet was hanging over my workbench while i was grinding the buttons/holes hence the notes to self in sharpie.

First 2 Buttons!

First two buttons, cut out of a scrap piece of clear plastic with a dremel tool.

Button Assemblies

Here you see the button plate mentioned in the blueprint, as well as the rubber buttons and plastic ones placed on top of the contacts.

A closer view of the button plate- just a length of perf board with wires soldered carefully to create contacts.  Tricky work.

More Buttons!

7 buttons here, you can also see the scrap plastic they're being cut from. You can also see one is in the process of being cut from the scrap.

Starting to Cut Holes

Starting to mark up the holes for the buttons. Here, i've drilled all the pilot holes, from here i take the grinder bit of the dremel tool and carefully enlarge each hole by hand.

Redesigning the buttons

So after a couple days of testing, i realized that using calculator style buttons just wouldn't work.... They were woefully innacurate and unreliable, required a massive use of force on the delicate reflector cup and on top of everything, i couldn't find a single glue that would bond to the rubber! So- i redesigned the buttons to use pushbutton switches, which were much more reliable, and to also put the LED and reflector directly under the button, making them brighter!

Reflector Cup Testing

Here you see a reflector cup, which is glued to the underside of each button.  I found aluminum foil to be the easiest material, it molded well and was quite reflective! The form is created by pressing an LED into the center of the square, then using a pencil stub to round out the shape.

And here is the reflector cup in action! I was quite pleased with the results- the reflector cup provided  a fairly even distribution of light from the LED across the surface of the plastic buttons.  A cheap and dirty method, but hey- it works!

First two buttons

First two buttons finished! (Only 14 more to go...)  They light up quite nicely, the matte plastic above the reflector cup gives a nice pearly swirl.  Or a rather trashy look... depends on how you see it! These actually look much brighter than they do on the photo.

First button mounted

First hole rounded out to fit a button, and now the button slides in and out nicely.  Hand grinding the holes does lead to pretty organic edges though....

4 buttons mounted

Progress!  1/4 of the way through.  The process for all these holes/buttons is the same, and to an extent, its fairly efficient!

More Finished Buttons

Now i have 2 rows of buttons finished! Almost a handfull. Same can't be said for the holes though... Though these look a tad mismatched, their dimensions are all within 2mm of the original button.

Closeup of the Button Holes

What you see here is a closeup of a hole in the process of being widened. The nearby holes have organic edges, but they accomodate the buttons well, so i'm not too worried. The dremel tool heats up the plastic and partially melts it, creating unique patterns in the plastic.

Low on plastic, plenty of buttons

Meanwhile, i've been running out of the plastic scrap i'm cutting the buttons out of! Thankfully, with a bit of careful cutting, i'll just be able to fit all the buttons on it without any size changes!  Also, as you can see, we now have 2 rows packaged! And 11 finished buttons total.

Electronic buttons

 Now for the actual electronic aspect of the buttons- earlier in the project, i planned on using soft rubber buttons similar to calculators, but as those proved unreliable, i turned to trusty old pushbutton switches (SPST), which i conveniently liberated from a VCR panel....

And here you see the buttons all mounted and soldered in place! This is a generic perf board, originally intended for microchips, but easily adapted for anything else! The strip of metal running throughout the board conveniently acts as the output.

Mounting the Button Assembly

 Finally got around to mounting the first row of buttons! Hot glue is a very versatile tool, and it does its job quite nicely! The button board is put in place to make sure the buttons set correctly and operate well once the board is removed.

And here you see the buttons connected to the board.  This happened to be very finicky wiring job, i wished that i had an third hand many times in the process.

Second Row

Second row is in place! Lots of filing involved in making the buttons fit snugly in the cover plate. Hot glue seems to be working fairly well as a mounting agent.