Tsukure Mad Labs 4-Channel Opto-Isolated Switch Circuit

Opto-Isolated Switching Circuits allow a trigger device to switch secondary devices that use a different voltage.

This particular module has many uses for triggering circuits from a Raspberry Pi or Arduino based micro-controller such as lights and motors.

This project was originally inspired by the need to trigger certain 12 volt circuits for our Artificial General Intelligence (AGI) project, TAU.

The problem; Arduino's and ESP32 microcontrollers user 3-5V trigger signals from their respective output ports. The circuits we wanted to trigger had a 12 volt source and load, the two voltages being very different.

The solution; Use light to isolate both circuits! Yup that sright light, as we know, can induce a small current to flow, just enough in fact to throw a transistor. This could be achieved by using a photo-cell connected to a transistor and LED light source powered by the microcontroller. Messy, but doable.

Thankfully someone else also had the same idea and developed it further creating what we now call an opto-isolator. An opt-isolator is essentially a phot cell and infra-red LED emmitter sealed in a case.

This project uses four opto-isolators to tirgger four transistor switches thus allowing a secondary power source to supply whatever load it is you wish to power.

Components used in this module...

Find out more about the components used in this STEM Module.

Let's Get Started!

Below you will find a list of bits to gather before hand, followed by a detailed schematic. Using a breadboard lay out the components and connect them together as shown. Alternatively you can purchase this module from our shop and simply solder the components in the places indicated on the quality assured printed circuit boards provided.


What You Need...


15 Male Pin Header Connector (Male)
4 EL817 Opto-Isolator
1 Tsukure Mad Labs - 4-Channel Opto-Isolator PCB
4 2N2222 Transistor (NPN)

NB: Any resistor colour codes specified relate to 5 band resistor codes, the 5th band has not been shown intentionally. The 5th band indicates the resistor tolerence, we use only the highest tolerence resistors in our products.

Take a Closer Look!


Let's Get Building!

We to build, so let's get to it! Gather your components as specified in the components list above, or simply order one of our project packs and tip the contents out onto your table or desk.

Solder station warmed up! Snips at the ready! Here we go!


Step 1) Getting Started

Before we begin placing components and soldering we should first place your components in a small tub so that they don't roll off your table or get lost.

Lay the PCB out infront of you and take a close look at all the components we will be using.

Furher explanations and detailed specifications of all these components can be found in our Wiki.

Step 2) The Trusty 2N2222 Transistor

You will find no other transistor so noteworthy as the 2N222, well except maybe that toe rag the BC549. Anyways, this project is designed to isolate a trigger voltage from a driver voltage. This means that we can use a low trigger voltage of just a few volts, say 3V, to drive 12V LED or motor circuits.

In fact you can do this using only 2N22222 transistors, however, this will not isolate your trigger source and requires additional circuitry to protect your trigger source. 

In our case we will be protecting are two circuits using light! For now, insert the four transistors into the board aligning them with the symbols printed on the PCB, then solder them in place.

You may need to bend the outer pins outward, and ensure the flattened side is properly aligned befor soldering.

Step 3) Isolation

We will now place and solder the four Opt-Isolator integrated circuits (IC's). These small chips


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Product Suggestions

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Tsukure Mad Labs - Arduino Nano Companion
Tsukure Mad Labs - ESP-32 DevKit Companion

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