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How to wire opto switches & opto switch boards in a FAST 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

Since we are just now in the process of creating the wiring guides for the upcoming general availability of the FAST Neuron Controller, this guide is not yet complete.

Opto Basics

Opto switches are a bit more complex than mechanical ones, but still pretty straightforward. An opto switch is made of two parts:

  • An infrared LED (called an "IR emitter") that shines a beam towards an IR detector.
  • An IR detector which operates like a switch which is "on" when the IR beam is hitting it, and "off" when no infrared light is hitting it.

The following drawings illustrate this process. The IR emitter is an LED that's always on, nothing fancy. It's a normal LED except instead of its color being red or blue or green, it's infrared. The IR detector is like a normal transistor, except instead of the base leg being the wire where a little current controls the transistor's "switch" effect, it's a light sensor. That transistor is packaged up as an IR detector by being wrapped in a special translucent plastic that only allows infrared light to pass through. (That's why they look dark purple, like the lens covers on your 1990s VCR.)

When the IR light is hitting the detector, the switch is "on" and reported as active.

When the IR light does not hit the detector, like when a pinball or plastic tab is blocking it, the switch is "off" and reported as inactive.

One thing about opto switches it that they're backwards / inverted (or "normally closed / NC" as you recall from the previous guide on mechanical switch wiring). So an opto shows as open/inactive when a ball is there or a target is down or a button is pushed, and it shows as closed/active when it's actually not being blocked. This is no problem, as you can configure the switch profile to be NC in the FAST hardware or the switch settings in your software and then treat optos like any other switch.

Wiring optos is also straightforward. Since each opto switch is a paired IR emitter and IR detector, we'll cover the wiring of each of them separately.

Wiring your opto emitters

Opto emitters are just regular LEDs that shine infrared light instead of a color humans can see. Nothing special other than that. They are always on. No pulsing or codes or PWM. Machine on = optos on. Easy peasy.

Of course LEDs come in many shapes and sizes which means infrared LEDs also come in many shapes and sizes. Some are the old-school beefy through-hole designs, and others are teeny-tiny surface mount ones which are attached to little boards. Sometimes you'll wire up a single emitter (like for ramp entry detection), and other times you might have a board with a whole bunch of emitters (like a trough opto emitter board).

As with all LEDs, you need to provide them with the proper voltage so they can consume their correct amount of current. If you just hook up an LED to your 5V power supply it will most like explode instantly. (It's fun, like tiny popcorn.) You need to do some math to calculate the watts and ohms for a resistor to add to the circuit to drop the voltage to a suitable level. And then you need a way to mount that resistor, and ... this is the reason the FAST 4-channel constant current opto emitter board exists:

This board takes 12 volts from your 12V bus and then powers up to four IR emitter LEDs. This board is small (about 1.5" square) so you can mount them near your LEDs, and it outputs the proper voltage which it automatically adjusts depending on the LED's current (hence the "constant current"). The output pins are labled "Anode" and "Cathode" (A or K, yes cathode is abbreviated K) which will match the labeling for the IR LED you're using.

Wiring your opto detectors

While the opto emitters are just IR LEDs, the IR detectors are essentially just switches remotely controlled by IR light. IR detectors are wired like any other switch, directly to one of the 11-pin switch headers on a FAST I/O board.

The only "catch" with IR detector wiring is that polarity matters. You must connect the "Collector" (C) to the numbered switch input (orange wire), and the "Emitter" (E) to the shared switch ground return (purple wire). (If you get this wrong, it probably won't break anything--it just won't work.) Other than that, treat an IR detector like a normal switch. You can use the same daisy-chained purple wire to connect multiple mechanical switches and IR detectors (to the "E" pin). Just remember that both leads of the IR detector must go back to the same I/O board!

As mentioned already, IR dectector switches will appear logically inverted, in that they will be active when they are not blocked, and blocking them makes them inactive.

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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