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How to wire the soft power switch & solid state relay in your Neuron-controlled pinball machine

Wiring, high voltage, and electricity can be dangerous. Read this first!

The voltages and electricity discussed here can be dangerous and could cause property loss or death. It is your responsibility to ensure you are aware of these risks and comfortable with these processes. Furthermore your local jurisdiction may have regulations or rules which differ from what we discuss here, including wiring colors, standards, techniques, etc. Although based on broadly adopted methods, FAST Pinball does not employ Professional Engineers and this information is not professional recommendations. There may be errors, omissions, or typos here. Any pinball machine available to the general public should be reviewed by a licensed Professional Engineer in your region. Use this content at your own risk.

If you're planning to use the soft power switch option we discussed in the previous guide, this guide will show you how to wire the pieces you'll need in your backbox. (To review, the soft power switch option allows the Neuron to control your machine's power, rather than using a traditional AC line level switch.)

If you're not using the soft power switch, you can skip ahead to the next guide.

This feature is coming soon

The code for the soft start feature is not currently complete. It will be delivered via a future firmware update for the Neuron. You can design your machine for this and build your hardware now (and just use the regular power switch for the time being), with full soft start and soft power off coming in the future.

What is a solid state relay? (SSR)

The FAST soft power switch feature uses a solid state relay (SSR). An SSR is similar to a standard relay, except it's solid state instead of mechanical. SSRs are everywhere in the industrial automation world, so they're perfectly designed to modernize a pinball machine's power control system too!

Here's an example of an SSR we like, from a vendor we trust: Panasonic AQA221VL (15A, 75-250VAC). It's pretty beefy, since it's carrying the full AC input load of your machine, and it'll need a heat sink and thermal fuse too, but it's designed for this type of use.

The SSR itself is pretty straightforward. There's a low voltage input side (this one can use anything from 4-32V DC), and a high voltage controlled "load" side (this one can take 75-250V AC, up to 15A continuous / 150A surge). Besides the labels, you can tell which side is which because the high voltage AC side has a plastic cover to help ensure people don't touch the high voltage terminals.

If you don't want to use this particular SSR, that's fine, but please don't pick a cheap one from Amazon. They are not safe! We like this SSR because it's from Panasonic, a large global company, and sold via Digi-Key, an electronics supply company whose self-interest is preventing counterfeits and random untested brands, and so we trust that the safety certifications listed in the data sheet are real. While testing the soft power feature, we bought several cheap no-name SSRs from Amazon and took them apart, and did not find any that we can recommend.

That said, if you buy your own SSR, the Neuron's SSR control voltage is about 6 volts, which any SSR should support. Make sure you get one that can support the necessary sustained current on its AC side (the SSR we recommend is 15A), and that it supports your AC input voltage (120 or 240VAC), and that it can support a temporary surge current of whatever the combined inrush is from your power supplies. (The 48-volt and 12-volt supplies we recommend have combined inrush of 100A, which is why our recommended SSR can take a 150A surge.)

Heat sink & thermal protection

Regardless of what SSR you select, you'll need a heat sink. If you're planning to cover your high voltage power area in a metal cover, you can use the cover itself as the heat sink. (Just drill two mounting holes in the metal cover, smear some heat sink compound on there, and run two machine screws through it with nuts on the outside.)

If you're not building a metal cover (or if you don't have one yet), you can buy a heat sink on Amazon. Luckily there's a standard size for SSRs and for this part cheap Amazon ones are fine. So just search for "ssr heat sink" and pretty much whatever comes up is fine. Maybe this one for 8 bucks? If you don't have heat sink compound paste, some heat sinks come with a little tube of it. (Heat sink compound paste is like toothpaste you smear between the SSR and heat sink which ensures a solid thermal bond is created.)

We also highly recommend installing a thermal fuse when using an SSR, as is common practice in professional applications and required by many safety jurisdictions. The thermal fuse is simple: it cuts the power when a certain temperature is exceeded. (125ºC in the ones we like.) They are tiny and only cost a few dollars:

Search Amazon for "ceramic thermal fuse" and make sure you pick one(s) that support the current you need (15A to match the SSR) and a temperature like 125ºC. Also, we HIGHLY RECOMMEND ones with wires attached that you can use with crimp-on connectors. The ones that require soldering will likely blow from the heat of soldering. Those require special soldering irons, skill, and/or spot welding. :)

You'll wire this thermal fuse into the AC hot line going from your power switch to the SSR. Then screw mount this fuse into the metal cover, heat sink, or other location on the SSR.

How does the SSR integrate to the Neuron-controlled pinball machine?

So now that you know what an SSR is, let's look at how it's wired into your FAST Neuron-controlled pinball machine. Here's the same power box diagram from our previous guide on AC power supply wiring, but with some more components added. Specifically, you'll notice the new Solid State Relay and a thermal fuse. The relay's AC outputs are connected into the machine's AC line input wiring, which gives the Neuron the ability to control machine power. (The Neuron will be wired up to the input side of the SSR.)

As mentioned, the SSR needs to be in the covered power box area since it has high voltage AC power connected to it. One of the SSR's AC output terminals is connected to the remaining free lug of your SPDT switch. This is what allows that switch, when in that position, to defer to the SSR to control power to your machine. Instead of running a regular wire from that switch to the SSR, use a thermal fuse with wire leads.

If you trace the other black wire from the output side of the SSR, you'll see that it just goes to the PSUs to power them. In the diagram it uses the other lug of the power switch for convenience, but it could've just as easily gone down to the PSUs themselves.

This can be a bit confusing to envision, so look at the same diagram tracing the AC hot wire path from the line cord to the power supply, with the power switch in the SOFT position:

If you want to bypass the SSR and let your machine power on automatically when power is connected, like in a commercial arcade where a service panel breaker is used to power on all machines, then you can move the switch over to the ON position since that will bypass the SSR. Zooming into the diagram above, the power mode selection switch in the ON position would look like this instead:

If you pick an AC switch with a center OFF position, you can use that position if you want to take the machine out of service, since it will not allow the machine to power on regardless of whether it's plugged in or the cabinet power button is pushed.

Understanding the Neuron's role in the soft power on

The FAST Pinball soft power solution requires a Neuron to work. You connect wires from J3 labeled SSR, pins 1 & 3 on the Neuron to the DC input side of the SSR. Then you connect a low power momentary pushbutton switch to J4 labeled PWR SW pins 2 & 3. This pushbutton will be the main power switch that users will use, so put it wherever you want that to be, most likely in the lower right front corner of the cabinet.

The Neuron requires a 2032 battery to be installed in order for the soft power on function to work. This battery solves the "catch 22" problem of how do you get the low voltage to trigger the SSR when the machine is powered off? Answer: from this battery! This battery is only used when the pushbutton switch is pressed to turn on the machine. Once the machine is on, the Neuron powers the SSR from its own 12 volts (which it gets from the 12V PSU whose input power flows through the SSR. Trippy!) This means this battery should last for years, and if it ever wears out, you can still power the machine on by flipping the AC switch in the backbox from the "soft" to the "on" position.

Here's how the Neuron is wired into the rest of the soft power solution:

The Neuron is also involved in the power off process. When the player presses the soft power button in the cabinet to turn off the machine, that just sends a signal to the Neuron. The Neuron can be configured for different options here, including powering off immediately, or delaying power off by a few seconds to allow for the host PC to shut down cleanly. (The Neuron also has a host PC header which can use to actually hit the power off button on the PC. Actually this can also be used to power on the PC once the machine power is up.)

Power switch location options

If you use the soft power solution, the main power switch will be the low voltage momentary pushbutton in the front right corner of the machine under the cabinet. Pretty simple.

But what about the AC line switch? (This is the one that controls the three modes of operation: ON, OFF, and SOFT.) Where should that switch be located?

In the previous guide, we showed locating the AC switch inside the backbox, in a location that was inaccessible to players and random people walking about. Locating the switch here lets it act like a "mode of operation" switch which controls whether the machine powers on automatically when the wall socket gets power, or whether it uses the soft switch in front, or whether it's off and out of service. We think this is a cool feature!

However, the downside to hiding the AC switch inside the backbox means that if the 2032 battery ever dies then the machine won't be able to start. (It would be like a car with a dead battery.) The workaround, if you don't have a spare battery, would be to flip the switch to the always ON position. But that would require someone with a key, and then also the machine power would be controlled by, what, yanking the power cord out of the wall? Not ideal. (Of course if you replace the battery it would be fine.)

If you don't want to risk a dead battery requiring a key to start your machine, you could instead locate the AC power switch so it was accessible from the outside of the machine. You could still use a 3-way switch with on/off/soft settings, and you could still use the pushbutton switch under the front of the cabinet for most power operations. But if the battery died, then the AC switch in the back could be a backup switch.

It doesn't matter from an electrical standpoint which option you choose. This is purely a future convenience thing to think about.

Shopping list for this step

  • Solid State Relay: Panasonic AQA221VL (15A 75-250V)
  • Heat sink for SSR
  • Ceramic thermal fuse
  • Momentary pushbutton switch for your cabinet
  • 2032 lithium battery for the Neuron

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