Subsystems and Subassemblies

We’ve started connecting cables to dedicated PCBs.

From now on, I’m going to use illustrative representatives of some of these components as they are introduced (Figure 6-14). These diagrams show the parts and highlight only the essential ports, headers, and plugs required to wire the arcade.

Figure 6-15 shows what we’ve connected so far: mainly, only dependent connections in between the LCD, driver panel, and button panel.

The HDMI-compatible LCD I’ve chosen is video only. Later versions support audio, but this batch does not. Next is audio.

Figure 6-16 is off-the-shelf 2watt stereo audio amp board. There are many DIY audio amps out there; this is just one. This PCB gives enough audio output to fill a small bedroom (with the right speakers), so this should be plenty for this sized arcade machine. The board also have built-in volume control with buttons and external headers to route volume controls somewhere else.

Matching speakers is easier when you have narrowed down your amplifier choice. This amp is compatible with speakers that have 4 to 8 ohms impedance. The speakers you select should be midrange speakers (Figure 6-17). This means these speakers can reproduce frequencies in (mostly) the full audio spectrum. Full-range speakers do not perform particularly well compared to dedicated speakers for dedicated low (subwoofer) or high (tweeter) frequencies. But we only have room for one pair of speakers, hence the choice for full range speakers. On this scale, this is our first big sacrifice, but you’ll likely won’t notice we skipped out on audiophile sound on 8- or 16-bit soundtracks. So, what speaker should we use? As big as possible. I’d pick the largest speaker (in physical size) you can fit in your cabinet. The size is proportional to the volume it can produce. This cabinet can comfortably fit all these sizes shown in Figure 6-18. Pictured are (from left to right) 3″, 2.5″, and 1-inch-diameter full-range speakers. Cheap speakers sound, well, cheap. The speakers pictured are about $4–$6 each or $8–$12. This is defiantly on the low range of things, but far from the bottom of available options. Considering I am not an audio engineer, I’d just be doing high-end audiophile speakers a disservice.

The 1 inch speakers will fit underthe marquee as we planned. These 1 inch speakers are for those who insist the speakers should be under the marquee. Figures 6-18 and 6-19 show a cross section of how I mounted these 1 inch speakers.

The mounting holes molded into the speaker baffle are ridiculously small; a #2 (~M2) screw doesn’t fit, so I opted for the sandwich method. More measuring is involved, but the mount is cleaner and more versatile if you wish to swap these speakers for say LED rings in the same location. (Hint, we’ll do that too.) The panel highlighted in green slips over the end of each speaker and retains them by being locked into the control panel with the centered nut and bolt.

But what if you want that larger speaker sound?

The 2.5 and 3″-diameter speakers will fit inside this cabinet. They will face the back of the LCD and project to player. Since they are inside mounted the cabinet body, there will be accidental acoustic properties of our cabinet, both good and bad. Some ranges have a richer, fuller bass sound; other ranges will be a bit muffled. I have other plans for the interior space of this cabinet, so instead of using the 3″ speakers, let’s settle on 2.5″. We need to build the subassembly shown in Figures 6-20 and 6-21. This is done by mounting the speakers and amp with machine screws. Don’t forget to solder wires of the left and right speakers and connect them to the respective audio amplifier.

Since we are looking at the rear of this speaker subassembly, the stereo left speaker is actually wired to the right (your directional right) output and vice versa (Figure 6-22).

Don’t forget to mount two standoffs on this assembly. These are 1 inch female/female aluminum standoffs shown in Figure 6-23. These will come in handy later when we need an easy way to fasten the rear panel to cabinet.

Use the two identical brackets shown in Figure 6-24 and mount the speaker subassembly into the cabinet, but don’t actually do it! We still need access to the interior the cabinet, so set this speaker assembly aside for now.

Updating our connection diagram brings us to Figure 6-25.

Control Panel Assembly

It’s time to assemble and wire the control panel for our arcade. There are two routes we can take with the control panel in conjunction with the Raspberry Pi. Because the Raspberry Pi has GPIO pins, we could use some software to poll the GPIO pins and interpret button presses and joystick inputs as keyboard inputs. The other route (and more universal) is using a keyboard encoder. The keyboard encoder is exactly as it sounds; it takes discrete inputs and encodes them to keyboard signals. You press a button, and the Raspberry Pi (or any PC that accepts USB HID devices) see a keyboard key activated. This is simple and essential component to build large-scale Multiple Arcade Machine Emulator (MAME) cabinets. It’s also my recommended way for MAMES with two or more players. I prefer keyboard encoders for single-player RPi cabinets too; that’s more because many of these encoders include wiring harnesses and I hate wiring. We will look at each approach.

In either regard, we need to populate our control panel and assemble the layers. First, mount the joystick (Figure 6-26) with flat head screws and split washers to keep the nuts secure during heavy use.

If you printed, cut it out and place it on the top of the control panel. Place the clear acrylic over and fasten with the binding posts (Figure 6-27).

Insert your buttons of choice. I’m using some smaller general-purpose push button above the arcade to save not just space but cost. You should have something like Figure 6-28 or 6-29 now.

You can place the joystick dust cover (the flat, black plastic disk) on now and screw on the ball top if you like.

Flip the control panel over; now it’s time to wire each input to the keyboard encoder, pictured in Figure 6-30. If you bought your encoder on eBay, hopefully (and usually) it came with a wiring harness.

This takes all the pain out of a rather tedious and repetitive task. Figure 6-31 shows a fully wired control panel. Each button gets a wire pair and plugs into its respective place on the encoder. More arcade keyboard encoders will have some generic wiring labels (button 1, button 2, or K1, K2, K3 in our example) to guide you.

Note the USB type B female connector on this keyboard encoder. The included USB cable will connect the encoder to your Raspberry Pi (Figure 6-32).

We haven’t installed the Raspberry Pi into the cabinet yet and for good reason. Another option for implementing arcade controls is done by wiring directly to the Pi’s GPIO headers. It’s best to do this with easy access to the Pi, before it’s mounted into the cabinet.

The extra software you need is Adafruit’s Retrogame found here at their github repository: https://github.com/adafruit/Adafruit-Retrogame

I recommend following the associated instructions from Adafruit: https://learn.adafruit.com/retro-gaming-with-raspberry-pi

Because this file exists in/boot, you can edit it easily: either locally on the Pi or remotely via SSH.

Wiring the joystick and buttons inputs to the RPi is simple since no pull-up resistor or additional hardware is needed. It is a tedious task to wire ten buttons with four directional inputs, all with a duplicate path that returns to ground. There is something we can do to assist with what goes where.

I’ve wired this before, hundreds of times. And I despise it. So, to ease the pain, I’ve got a few pro-tips or quality-of-life improvements. We’ve already settled on a button/keyboard mapping as defined in the example config file. Trust me, you want to settle on something before continuing.

We are going to make another cheat sheet! Just like the one in Chapter 6, but instead of GPIO numbers, we just put the intended arcade controls on the sheet. See Figure 6-33.

Print this out to scale and smash it onto the RPi’s GPIO headers. Now we don’t need to go back and forth translating what button input is assigned to what GPIO pin. Following the cheat sheet, the “Start” button is wired like in Figure 6-34.

Just repeat the signal and ground wire connection for the rest of your buttons and joystick inputs. Speaking of joystick inputs, this is another one of those mirrored image brain teasers. If you’re looking at the bottom of your Sanwa joystick (you likely are at this step), the directional inputs are arranged like in Figure 6-35.

I usually transcribe this in pencil on the underside of the control panel as I’m wiring. Basically, do as much prep work in advance to avoid wiring something wrong. This is usually (it will happen to you) where a wiring issue will arise.

Keeping with the unfortunate theme of wiring diagrams, if you wire all your arcade inputs to the RPi, it’ll look something like Figure 6-36, but with fewer straight lines. If you are a messy point-to-point wirer, rest assured! We’ll just stuff that mess away in the cabinet to definitely not have to troubleshoot later. My button layout is just that, my button layout. If you want to move placements around or enable hotkeys, do so! Please take some time to stare at this diagram. It’s very helpful and also took too much to draw.

You’ve either got no wires connected to your RPi right now (you’re using a keyboard encoder) or a pile of spaghetti poking sticking out of the Pi’s GPIOs. Either way, the control panel is complete. This is a great time to mount the Pi into the arcade. Place the control panel into the arcade and add the locking bar like in Figure 6-37.

Add two screws into the rear of the control panel cross brace, and loop a rubber band over these around the control panel locking bar (Figure 6-38). I still have not drawn a rubber band here.

This will keep the locking bar in position. Place the long screw through the top of the control panel; fasten with a thumb or nut (Figure 6-39).

Next, focus to the rear of the cabinet (Figure 6-40).

Add the Raspberry Pi riser plate along with four mounting screws (Figure 6-41).

Add nylon spacers (optional) so pressure is transferred into the RPi PCB and not the through components protruding under the RPi. Mount the Pi, add nylon spacers, and fasten with nuts (Figure 6-42).

With the integration of the main control panel, we need to populate and wire the remaining buttons in the cabinet. Figure 6-43 shows some extra hardware needed.

Figure 6-44 shows where we add some extra function buttons under the marquee, two of which we will use for amplifier’s volume up and volume down. The remaining two will be latching switches, of which are placeholders for optional features later on.

First solder wires to the buttons and switch contacts. Feed the wire into the mounting hole followed by the attached buttons and switches (Figure 6-45). Attach the plastic retaining washer from the inside.

The rear of the cabinet has two large access panels (Figure 6-46) to help us wrangle these wires.

The volume buttons are wired like in Figure 6-47, giving us volume control from the front of the cabinet.

With the rest of the hardware placed in the cabinet along with the appropriate controls (on/off switches) installed like in Figure 6-48, it’s time to wire power. These switches will control power, the backlight marquee lights. On the rear of the panel, we also mount the DC input jack, where main power enters the cabinet.

There’s a lot to talk about in the next steps, so new heading!

Animated LED Marquee

First off, the marquee gets an upgrade. Replacing the static backlit graphic panel is an 8x48 LED matrix driven by an Arduino Nano inside. Figures 6-70 and 6-71 show the 8x48 LED matrix segment fitted to a mounting panel and driven with a custom Arduino clone board (not in the arcade). The individual 8x8 matrix segments are MAX7219-based modules, easily found on eBay (about $4 for a series of four connected matrices).

The required Arduino libraries to drive them are MD_Parola and MD_MAX72XX. A future project for me is to drive them with the Raspberry Pi and write a script that scrapes the ROM name currently loaded and pushes the string to the marquee. Someday.

Battery Powered

I mentioned in Chapter 5’s Design Review, this arcade is small enough to make it battery-powered. Let’s give that a try! After all, we have the room and planned for this: the larger cabinet size and the internal storage shelf. I have some Ryobi power tools I use at home, so let’s see if we can utilize a battery pack readily available, the cordless Ryobi battery in Figure 6-72. This can be any drill battery you have or any battery pack that outputs at least 12V.

I rebuilt the inner shelf as a power regular with a custom step-down converter. Since the drill battery is 18v (nominal), we need to step the voltage down to the input power we design the arcade electronics to run off, 12v.

The rebuilt inner shelf shown in Figure 6-73 has a custom 3D printed bracket (Figure 6-74) that contacts the battery’s + and – terminals when inserted. With this battery, I get about 2.5 hours of run time; that’s with normal screen brightness and medium sound volume.

The battery voltage, which varies from 20v to 16V (from fresh to dead charge) is regulated and passed to the arcade. You can see the current voltage of the battery pack in Figure 6-75. I have plans to make a battery level indicator on the outside, rather than having to peak at the number to determine when the battery is near empty charge.

Neo Pixel LED Lighting

My last modification features some Neo Pixel LEDS that add some multicolor glow to the arcade (Figure 6-76). These Neo Pixels are individually addressable, so each LED’s color can be assigned in a stip.

The extra buttons below the marquee toggle if these LEDs are on or off; since now that we have battery power, we want the ability to turn off nonessential features when playing the arcade. With the top access panel in place (Figure 6-77), this gives a dark room a soft glow from the inside LEDs.

Finally, remember our design used the 2.5 inch speakers mounted behind the LCD? I demonstrated how to mount 1 inch speakers below the marquee, but in the end we did not install them. So, what did I do with that space? The same mounting principles applies, but this time I mounted some Neo Pixel LED rings (Figure 6-78).

You might have noticed a multicolored glow earlier; this is the Neo Pixel ring (Figure 6-79).

Keyboard for a Joystick

Retro arcade games work great on arcade joysticks. But what if your fancy is more PC-based? Some retro PC shooters emulated on DOS box perhaps? Compared to a keyboard, an arcade joystick does not have the same feel when playing 1990’s First Person Shooters. Let’s replace that joystick with a keyboard PCB! First, the custom PCB design in Figure 6-80. I’ll refer to this as a key-stick because I can’t think of anything better to call it. I’m still experimenting with the idea at this time.

Next, solder keyboard switches (Cherry MX of course) and resistors for 3mm LEDS in Figure 6-81.

Though optional, you can’t call yourself a gamer unless you have backlight mechanical keyboard keys (professionals have RGB backlit keys). Refer to Figures 6-82 and 6-83 for LED installation and backlight testing. Why red LEDs? It’s what I had. Why orange keycaps? Again, it’s what I had. I didn’t plan for this very well.

You might notice two “Esc” keys. The keycap sample packs I bought only have so many unique keys. Let’s just call it a place holder for now.

The control panel requires an overhaul. I wanted to avoid this looking like a drop in number pad, so I’m only using eight keys plus two offsets. Figure 6-84 shows the rear view of the control panel. This is mounted the same way, with four flat head screws.

Note the two pencil lines. To make this key-stick a nontrivial hardware swap, I wanted the main arrow keys to match the exact same order of the Sanwa-JFL joystick. The arrow keys are wired as such on the PCB. To facilitate that easy swap, the interface needs to match; male 0.1" headers are the choice. I have a right-angle header sticking out of the key-stick in the same fashion as the Sanwa joystick earlier. The pencil line in Figure 6-84 indicates where this header is soldered to the PCB. The header is through-hole and protrudes out of the PCB—same side that needs to mount under the control panel. I have to mill out some wood with a rotary tool; otherwise, the key-stick will not sit flush on the control panel. Figure 6-85 shows the routed channels.

Finished product is shown in Figure 6-86. I think I will move the keypad up about an inch. My wrist could use some more room when using this keypad.

I’m pretty happy with the key-stick as a concept. I just wanted to showcase some ideas that can motivate your arcade to something very custom. You can still incorporate the traditional trackball setup too, but never be afraid to experiment.

Don’t think the custom PCBs are a cost-prohibited accessory. If you ever need to design and layout a custom PCB, try Eagle CAD, KiCAD, or EasyEDA. Getting custom and professional PCBs are surprisingly cheap. These PCBs were about $0.50 plus shipping. Seeed Studio, JLB PCB, and PCBway are cheap, low-quantity manufacturers great for prototype circuit boards.