Steve and I had talked about making a tiny arcade machine for his little chibi Street Fighter guys (street fighter guys fighting each other but in their own game – very meta). It would be great a little project to make with the Replicator 2. So I got to thinking that it would be cool to make one, but a static piece of plastic would be too boring.
So while browsing Amazon one day, I noticed an odd little novelty item – keychains with a little 1.5″ screen to use as mini picture frames. Then it hit me – these would be a great bit to stick into my mini arcades – load ‘em up with some screenshots, and presto, nice little desk toy…
On Amazon the screen ran for about $11, but on EBay you can get these ones from HK for about $6; much better. They have their own little 3.7v battery which you can charge via the built in USB plug. So I built a features list:
- Should be easy to reach the USB plug for charging/changing the pictures
- You should be able to change the side/marquee art easily to change the theme of the machine
- All the features of the picture frame (it has a clock, auto off settings etc) should be easily accessible
- It would have little red illuminated coin slots at the front.
The first step was to carefully measure all the non-printed parts (the picture frames, tac switches, magnets and LED). Here are some keychain screens without their casings. Everything is square and therefore easy to print frames and attachments for:
Mostly the breakdown of the parts was based on printability (to avoid overhangs, etc). The sides I would attach with magnets – that would let you have easy access to the USB plug, as well as swap out the cabinet art. To avoid the problem of swapping out marquee art, I designed the machine to have no marquee (although an illuminated marquee would have been awesome too – maybe for V2).
So now off to design. I used OpenSCAD and InkScape again, and this gave me a good chance to learn some more features. They are a very good set of tools. Spending time designing in OpenSCAD pays off big time. Every hour you spend in design saves you two hours of aggravation after printing, kids. Here is the final design:
The cabinet consists of these printed parts:
- LED holder/coin slots (printed with natural PLA which is translucent clear, and works nicely as a light guide)
- shelf for tac switches (with indentations for each tac switch to ensure they are spaced correctly)
- cover/faceplate for the tac switches
- sides with theme art
Once I felt I had the design nailed down, did some test prints to make sure the enclosure would fit together, and find bugs (I write comments directly on the piece when doing this, as it’s easier than describing where the issue is).
There were a good number of issues I didn’t spot in CAD, so back to the design board to get those ironed out. Once they were sorted, I printed another prototype shell (which turned out to have only one bug in it, which I fixed in the production shape). I find natural PLA to be a good material to do prototype prints in, because it is translucent, and so you can see a little of how things interact internally.
But before I this prototype lit up, I had to take care of the electronics. On taking apart the picture frame, everything was fairly simple – there were four buttons to be surfaced on the arcade machine, and you could tap those directly on the PCB (even though they use surface mount – you just need to be a little careful with your soldering iron). I surfaced those conenctions to a little .1″ header, to allow me easier assembly. Here is where to tap the PBCs:
The one cool feature I wanted was a little light illuminating the coin slots. For that I needed to find a 5v source on the PCB. I ended up tapping that from the screen’s back light (which is on the other side of the PCB):
Add a resistor and LED, and you’re good to go. Here is the “electronics package” ready to be inserted into the cabinet. Notice it is running (to test I didn’t fry it during soldering), and also note one end of the header is painted red – that’s to allow me to connect it the right way round to the buttons later (flip it around and you could fry some stuff, so pays to put a little indication of handedness in there):
The next step was to put the switches into the cabinet. I super glued the button spacer piece to the cabinet body, and then hot glued the switches to the spacer (maintaining the correct spacing is important, because there is a little cover piece with holes that goes over the switches, and if the spacing is wrong the buttons will be obscured). I cut the legs of the switches in the following way to allow for better soldering.
All the bottom legs are wired together and then to ground (i.e switch 1 to switch 2 to switch 3 to switch 4 to ground), and then the top connection goes to one of each of the buttons we surfaced to the header in the step above. This part was a bit annoying, because the heat form the soldering iron would cause the hot glue to let go sometimes, resulting in a messy re-glue. I will have to try harder with superglue if I do this again.
The final electronics related step is to insert the LED into the LED ‘lens” which pops out through the coin slots. This is printed in natural PLA so that they light can shine through. I added some black electrical tape around the edges to ensure the light escapes only out of the front of the lens – it ensures a brighter light, and also prevents a weird red glow from seeping from the edges of the cabinet (unless you’re into that sort of thing).
Now the only thing left to do is hot gluing:
- Glue the coin lights to the main body
- Glue the screen to the screen frame
- Glue the screen frame (with electronics now attached) to the main body
- Glue the magnets into the main body receptacles
- Glue the button cover (over the switches) to the main body
- Glue magnets to the cabinet sides
- Glue the artwork to the sides
Here is all the bits glued in place (without the sides for clarity):
The idea of having the ‘quick detach’ sides is to easily change the artwork of your machine, as well as being easy to open for charging. Note that when you do steps 4 and 5 above, you need to be sure the polarity of the magnets is correct, otherwise the main body will “reject” the sides. I thought this magnet based attachment system would be better than having a peg/hole system, because the pegs might snap off; but the truth is hot glue is not great at overcoming the magnetic force, so the magnets will sometimes come off the PLA. If I were to do this again I would either redesign with a peg/hole system, or use one magnet plus metallic surface rather than two magnets (it would be half the force, and presumably the hot glue could hold that).
I had a lot of fun making this thing, so I decided to make a couple (I ended doing six, including the prototype), and give them away as gifts. One of the great things about 3D printing is that you can make multiple copies of anything (provided you have PLA and patience – printing the pieces for a single machine takes more than an hour). It is pretty satisfying, once you’ve figured out how they fit together, to knock out four or five cabinets in a single Saturday.
By loading different screenshots and customizing the side art, I came up with “themes” that the recipients would enjoy. I made a Street Fighter II theme, Classic Arcade theme, The Oregon Trail theme, Duke Nukem 3D theme, and a Classic PC Flight Sims theme. I printed out some instructions for each, added a little USB charging cable and put them in a nice gift bag for delivery. Here is my mini arcade, shortly before they all went off to their respective homes (click each for more sizes).
Here is a list of all the parts used:
- The STL files are available at Thingiverse
- 4x 4.5mm tac switch
- 1x 1.5″ keyring picture frame
- 1x 5mm red LED
- 12x 3mm x 1.5mm round magnet
- 200 Ohm resistor
- Card stock for cabinet art (template for the art is included in the Thingiverse project)
- Natural (transparent PLA) for the coin door light
- Whatever colour PLA you want for the body
- Hot glue
- Superglue (cyanoacrylate) – nothing glues PLA to PLA better.