An Ethernet Relay Board for the IoT

Alasdair Allan
2 min readJul 2, 2018

I see a lot of connected projects, and it’s always somewhat surprised me how infrequently people build projects that connect or control 110V or 240V mains powered things. After all, we spend a good portion of our lives surrounded by mains powered “things.” Surely makers have a burning desire to turn them on, and off, again? However there seems to be a built-in, “that’s too scary,” that kicks in, which means people won’t attempt to connect things to the mains in their projects.

So if you want to get started with controlling mains hardware, and you’re a bit hesitant, I really recommend the PowerSwitchTail. It’s a solid bit of hardware that isolates all the messy mains stuff away from your project and keeps things safe. But sometimes you need something a bit more, and this is where Open Electronics’ Ethernet Relay Board might come in rather useful.

The Ethernet Relay Board. (📷: Open Electronics)

The board is driven by a Microchip PIC18F67J60, and offers a single LAN interface and four relays capable of switching a maximum of 120V at 3 Amps. There are 8 programmable GPIO pins (operating at 5V), and 4 analog pins (operating at 3.3V) with a 10-bit ADC.

The board runs a web server to allow you to control the relays, GPIO, and analog ports via a simple web interfaces or via HTTP GET commands. You can also associate events enabling you to trigger relays or toggle the GPIO when threshold values are reached. So, for instance, you can use a photo-resistor attached to one of the analog inputs to trigger a relay to turn a light on or off.

The board offers a LAN interface, 4 relays, 8 programmable I/Os, and 4 analog inputs. (📷: Open Electronics)

There is a walkthrough of how to use the board on the Open Electronics site, and it can be picked up for €72 (approximately $84).