Mini Space Invaders DIY
Some months ago I finished an original Space Invaders restoration project but as you can see was a little big for my daughter.
So the other day I stumbled across a cheap 5.5 inch CTR black and white TV and I decided to make a “mini-me” version for her.
There are many Space Invaders scale models including this world tinniest but… they use LCDs. To make an accurate reproduction you need a CRT.
Also, one of the coolest things about SI is that, instead of seeing directly the monitor, they use a semi translucent mirror, with a moon and a backdrop behind all illuminated by a backlight to create the illusion of depth.
Sounds a little complicated by lets say that the resulting effect is unique and really cool.
The electronics will be, the mentioned TV and for the brains a Raspberry PI, but I will leave the electrocution for the end.
WARNING: CRTs are nasty dangerous devices even at 5.5 inches… I took a lot of shocks in my life but this one can kill you. So if you are going to make this project learn first how to discharge a CRT. Do not do improv here or will be your last act.
And now for the cabinet.
Im going to use 5.5mm MDF so that will dictate the scale. From the original 3/4 to 5.5mm.
Since I have the original machine was easy to get the angles and measurements but I was surprised to find a pretty accurate model in the Sketchup cloud repository that save a lot of time. I remodeled over it, corrected the angles and ended with something really close to original.
You can get the file with all the parts used to make this model here: http://www.thingiverse.com/thing:82583
Then this needs to go to the laser cutter so the next step is to “unfold” and flatten out the model. Most was cut in 5.5mm MDF. I used 3mm for small parts. It took two 60x40cm 5.5mm and one 40x40cm 3mm.
Next we need to glue the parts. Its important to no go to fast here. We need only the basic structure so its easy to mount the electronics. The front and roof will be glued at the very end.
Then it was the turn to dress up the cabinet. I discarded for this project the spray paint and stencils (for the next one!) so I printed decals. The trickiest one was the bezel. I printed in a translucent decal mirrored so I can stick it into the acrylic. Then I masked and spray painted with white the opaque areas. The result was nice.
Now the the side art fitter perfectly and the overall result was nice (not as good if I use stencils but works)
Now for the Coin door and speaker cover the idea was to 3d print them so I started again with Sketchup:
The actual prints resulted far better then expected.
For the bezel illumination I used standard LEDs and some resistors. This will be powered with the 12v TV supply so you ned to do some calculations. Regarding the LEDs, since they create a very narrow spot I used some cotton pads to diffuse them and the actual result was very good.
One importan detail of SI is the black light that illuminates the galaxy backdrop and the moon that goes behind the “one way” mirror.
For the moon I cut the outline in the laser cutter and then printed in a water-slide decal the art. One important detail is to add fluorescent paint so it react with the backlight. I used an Airbrush to get an even finish:
For the Black Light I was thinking in using UV LEDs but incredible enough I found this device to check counterfeited bills . It has a small UV tube that fits perfectly and make it much more accurate:
Then I 3D printed a new black light support similar to the one in the original cabinet. Here is the support and the end result:
One of the distinctive things about SI is that it uses a two way mirror to reflect the actual monitor. Its a really neat feature. The two way mirror is widely use for windows and was easy to get.
The control panel was a little but tricky since I wanted to use the Raspberry GPIO. I used an Arduino proto board to create the board. It really simple, just a few resistors to pull up the pins and protect the PI. You can get info of how to do it here. Then its all about running the service in the PI so it mame can recognize the inputs. (Be careful to not short-circuit or send the wrong voltage to the PI GPIOs or you will fry it).
For control panel plaque I cutter a 1,5mm aluminum plate with the CNC router and combined it with water-slide decal. When the decal dried out it looked like the original silk screen version.
The brain of the machine is a Raspberry PI. You need to install Mame and configure it so it directly launches SI. Also if like me you are going to use the GPIO you need to run a service so PImame detects those inputs. For the output we are going to use the composite video so we can connect it directly to our TV in. Same thing with Audio, from PI audio out to the TV audio in. That´s all you need.
Thats mostly it. Beside this the last trick was to power everything. I used the TV 12v to power the bezel LEDS. The PI uses a hacked Ipad power supply glued to one of the internal walls and the UV tube gets direct 110v volts. At the end all fits inside the cabinet so you have just one power cord coming out.So here is the end result. A Raspberry PI scaled version of the classic Space Invaders.