Raspberry Pi Arcade Machine

Purpose
A fairly inexpensive machine dedicated mostly to playing coin-op games from my childhood. It uses MAME (Multiple Arcade Machine Emulator) to play the ROMS from the original machines. It also can play movies and music using Kodi.
Parts List
This thing wasn't exactly cheap. It could definitely be done cheaper with a smaller monitor and lesser sound system. The total cost for mine was around $275. If you cut back on things you could probably build one for around $125.
1 x Raspberry Pi3, with power supply, HDMI cable, and Micro SD card - $60 https://www.amazon.com/gp/product/B01C6EQNNK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
1 x Plastic tote - $5 or so
2 x Joystick+Buttons kits - $16 each, $32 total - http://us.banggood.com/Wholesale-Wareho ... 39974.html
1 x 10" HDMI Monitor - $115 https://www.amazon.com/gp/product/B01D17GPI4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
1 x Audio Amplifier - $24 https://www.amazon.com/gp/product/B019MBUX40/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1
1 x Pair Car Speakers - $20 https://www.amazon.com/gp/product/B00INA9UBE/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
1 x AC Power Switch/Port - $6 https://www.amazon.com/gp/product/B00ME5YAPK/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
1 x Standard Computer Power Cable - $11 (I bought a really really long one)
1 x Miniature USB Computer keyboard (a bluetooth one would work too). I had one laying around, but I'll call it $10.
Retropie Linux - free - https://retropie.org.uk/
Instructions
Just connect it all together, copy retropi to your MicroSD card, boot it up, configure the joysticks/buttons in MAME, round up your MAME ROMS, and play!
I think it's harder to describe exactly how to build the thing than it was to build it. You'd benefit greatly from some Linux experience, some electrical wiring experience, some basic powertool experience, and you need to own some BIG drill bits. The big buttons require 1-5/8" holes I think. A hand router would probably do the job, too.
Kodi
I have Kodi installed, and with it comes all kinds of multimedia possibilities. Plug up a big USB hard drive with movies on it and it becomes a movie box. Add the Google Music (or spotify or pandora, etc...) addon and it becomes a party music machine.

Audio
I originally had a stereo board amp in it, sticking out the front. It was cheap ($12), but that thing was a pain in the ass. First off, it required 12vac. That's right - 12v AC. That means it can't be easily powered by a 12v LiPo battery should I want to make this thing portable. Also, I think one of the channels blew out after a few days of use.
I ditched the AC amp and sucked it up and paid $24 for a 12vdc-powered enclosed stereo amp. It didn't fit in the area in the front though, so I had to relocate the audio controls to the right-hand side of the tote.

The car speakers I got are two-way with a little tweeter in the center, and they sound very good when compared to your run-of-the-mill bluetooth speaker thing. This amp+speakers also get much much louder than any cheap bluetooth speaker I've run across.
Monitor

I wanted a 10" monitor, but if needed a lot of money could be saved by swapping out a 7" monitor (could probably save $60). The one I got has HDMI and SVGA inputs, but the HDMI input wasn't auto-detecting things from a cold boot. I had a spare HDMI->SVGA adapter, so I came HDMI out of the Raspberry Pi into the adapter, and then used a SVGA cable from the adapter to the monitor. That setup works perfect when power is applied and things boot up.
Joysticks/Buttons

I got the joysticks and buttons and USB gameport adapters from Banggood (USA warehouse). The item linked to in my parts list above is by far the cheapest way I've found to get mechanical joysticks and buttons for an arcade machine. At $15.77 per side (once side=one joystick, lots of buttons and wires, one USB controller board), two of them for $32 cost less than half of what you'll usually find equivalent parts on Amazon.

So, I wound up with two USB game controller things plugged into the Raspberry Pi. They work fine though, and it sees them as two separate joysticks.
AC Power Port

You could definitely omit this AC power port thing and instead use an extension cord or a power strip. I wanted an externally-accessible power button, and I wanted to be able to swap out the cable for a really really long one. I figure at parties you never know exactly where the arcade gaming might want to happen, or where the music might want to be. I got a 25 foot cable, which is super long compared to most computer power cords.
