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How to wire the solid state relay and soft power button 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 comfortable doing the things discussed here. Furthermore your local jurisdiction may have regulations or rules which differ from what we discuss here, including wiring colors, standards, techniques, etc. Seek professional guidance from someone local to you if you are unsure of anything you're doing here. Also there could be errors, omissions, or typos here. Use this content at your own risk.

This guide is for FAST Neuron-powered machines only

This wiring guide is for pinball machines powered by a FAST Neuron Controller. If you have a FAST Nano Controller, please see the Nano wiring guide.

The Neuron wiring guides are incomplete works-in-progress

NOVEMBER 2022 UPDATE: We are in the process of creating & updating the wiring guides for FAST Pinball Neuron-based systems. We are publishing our work-in-progress docs to get as much information out as soon as possible. If you have questions or want clarifications, please reach out via email to me (Brian), via

If you're planning to use the soft start 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. The full soft start solution requires the Neuron Controller and a cabinet switch, so for now we'll just focus on AC high voltage pieces you'll need in your power box area of your backbox.

What is a solid state relay? (SSR)

The FAST soft switch option is built around something called a solid state relay (SSR). An SSR is similar to a standard relay, except instead of the input controlling voltage powering a mechanical relay, in a solid state relay, that relay is... solid state! :) So it's an electronic relay, similar in concept to the MOSFETs on FAST I/O Boards which control drivers. (One major difference between a FET and the SSR here is you'll need an SSR which can switch AC voltage.)

Here is an example of an SSR mounted into a heat sink. It's pretty straightforward. There's a low voltage input side (this one can take 3 - 32VDC), and a high voltage control side (24 - 380VAC in this example)

You can select a simple SSR that has two input terminals (where you'll apply low voltage DC to enable the relay), and two output terminals which you connect your AC input hot wire through. (So from the AC side, the SSR is just like a power switch, but it's controlled via low voltage DC from the Neuron instead of a person flipping a switch.) Most SSRs have wide DC input voltage ranges, like 4-32VDC or 3-32VDC or something like that. Any of those is fine.

You will also need to ensure the SSR you select is rated for enough current for the combined inrush current ratings of your two power supplies. This could be a pretty big number, like 100A or 200A. (This is just the initial current spike when the PSUs power on. They use much much less current once they're running.) Most SSRs will have built in heat syncs that you'll need to consider in your power box mounting plan.

How does the solid state relay integrate to the Neuron-controlled pinball machine?

So now you know what a solid state relay is in general, 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.

Starting with the SSR itself, as mentioned, you want to put that in your 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 the that position, to defer to the SSR to control power to your machine. (If you trace black wire from the other bottom terminal of 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.)

If you want to bypass the SSR and let your machine power on automatically when power is connected, like in an 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. If you pick an AC switch with a center "off" position, you can use this 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 start process

The FAST Pinball soft start solution requires a Neuron to work. You connect wires from J3 on the Neuron to the DC input side of the SSR. Then you connect a low power momentary pushbutton switch to J4. This switch 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.

The Neuron requires a 2032 battery to be installed in order for the soft start function to work. This battery solves the "catch 22" problem of how do you get the voltage to fire 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 relay 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.

The Neuron is also involved in the power off process. When the user hits 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 start 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 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 rated for enough amps for your PSU combined inrush current
  • Momentary pushbutton switch for your cabinet

Documentation Feedback? Requests? Confused?

Hi! I'm Brian, and I'm responsible for the documentation at FAST Pinball. If you have any feedback, requests, corrections, ideas, or any other thoughts about this documentation, please let me know! You can email me at Thanks!

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