How to Build a DIY Solid

Solid-state relays offer more efficient switching for smart home automation projects. Build your own DIY SSR by following this guide.

You can buy both mechanical and solid-state relay modules. However, solid-state relays are newer and cost a bit more than the traditional relay switch modules that you might already be using in your DIY smart switches or home automation projects.

In this guide, we will build a solid-state relay from just a few readily available components. You can use these DIY solid-state relays in a production environment and in your home automation or smart switch projects.

Unlike mechanical relay switches, a solid-state relay has no moving parts. It's akin to comparing a mechanical hard drive and a solid-state drive, which is way faster and power efficient.

Similarly, a solid-state relay (SSR) works faster and does not consume any power when not in use or switched off. It works or switches on when the trigger voltage is provided by the connected MCU. Most importantly, a solid-state relay occupies a lesser footprint and does not make any clicking noise when triggered.

An SSR can also be used for inductive load switching. However, you must add a snubber circuit to the SSR to prevent damage to the TRIAC (triode for alternating current). This may not be required in some TRIACS, such as the BTA16.

Also, building a solid-state relay is cheaper than buying one or building a mechanical relay module. We have built a few and have been using them in a production environment for the past few months. They work reliably smoother with no issues to date.

You can choose to build a single-channel, dual-channel, or multichannel solid-state relay based on your requirements. To build a single-channel solid-state relay, you will need the following components:

You will also need to learn how to solder, if you've never done it before, for building this DIY solid-state relay module.

Get the general-purpose PCB board and connect all the components as shown in the following diagram.

It should look like this after assembling and soldering the required components on the board.

To test the DIY solid-state relay, you need a few wires and a 3.3V or 5V power supply. You can use any 3.3V battery or an MCU, such as a NodeMCU, D1 Mini, Arduino Uno, etc., to supply the trigger voltage required for testing the solid-state relay switch.

Testing the solid-state relay and installation involves dealing with a 110V-240V AC power supply. Please proceed only if you know what you are doing. This could be lethal if not done carefully.

When a 3.3V or trigger voltage is supplied to the solid-state relay, the internal LED or IR LED in the optocoupler turns on and starts emitting light to the optical sensor connected to pin 4 and pin 6.

As a result, the resistance between pin 4 and pin 6 goes low, which triggers the TRIAC and switches on the connected AC load. The optocoupler helps to separate the high-voltage and low-voltage circuits, keeping the Arduino or MCU safe from any interference or damage.

You may now connect the solid-state relay to an Arduino or other MCU. Instead of three jumper wires for a mechanical relay, you only need two for the SSR: one for the input signal (3.3V) and another for ground (GND).

Based on the load, you can choose higher load-bearing TRIACs, such as the BTA16, with a heat sink to build solid-state relays for heavy loads (2000W or more). Remember to use a snubber circuit if you are going to use the SSR for inductive load switching, such as for a motor or pump.

You can use these solid-state relay modules in your smart home projects. You can design ESP12-powered smart switch modules with the integrated solid-state relay using the electronics sketching tool Fritzing. Once designed, you can get the PCB printed from a PCB prototyping/manufacturing service provider or just keep using general-purpose PCBs.

You can use this relay to build a smart motion-sensing light switch or Wi-Fi switches and install them in your home or office. Smart devices can help you reduce energy waste to a significant extent besides being convenient to use. Further, you may also set up a Home Assistant server on Raspberry Pi to add automation.

Now that you have learned to build solid-state relays, you can replace your mechanical relays with an SSR for efficient switching and avoid clicking noises. With a lesser footprint when compared to mechanical relays, you can design and build prototypes or smart switches in much smaller 3D printed cases for your smart home project.

Ravi is an expert tech explainer, an IoT enthusiast, and a Linux lover with a background in big data and app development. He's a tech geek with over 7 years of experience in creating DIY tech and how-to guides on data recovery, file repair, Exchange Server, Outlook, Microsoft 365, Windows, Mac, Linux, iOS, and smart home.