Some of you may remember this from June — my dad and I built a CO₂ planter that looks more like home decor than a sensor. This time I'm sharing the firmware, wiring and everything you need to get the electronics up and running yourself.

My first version was basically a pile of jumper wires on my desk. It worked perfectly — my wife just didn't want it in the living room. 😄

So my father, a retired mechanical engineer, helped me turn it into a proper enclosure, my brother designed the polygonal shell, and eventually it became something that actually looks at home on a shelf.

This is **murCO** — an open-source Home Assistant device that happens to look like a little planter. 🌱

It measures **CO₂, temperature and humidity**, but the fun part is what happens when you connect it to Home Assistant.

The CO₂ level is easy to understand at a glance — just look at the colour. Even my kids can tell when the air is good and when it's time to open a window.

**And it talks.**

The speaker shows up as a native Home Assistant media\_player, so it's not limited to CO₂ alerts. Through HA automations it can announce pretty much anything you want — notifications, reminders, doorbells, washing machine finished… whatever you come up with.

The LED has adjustable brightness and day/night settings, and it can also remind you when the Tillandsia needs watering. 🌿

In Home Assistant you also get the sensor values plus controls for the speaker, LED brightness, day/night behaviour, watering interval, temperature alerts and more.

The large front diamond doubles as a physical button for quick local controls.

And that ended up being the whole point of the design:

**I wanted a DIY smart-home device that I'd actually be happy to leave in the living room.**

Something you can build at home, put on a shelf, and maybe even have a neighbour ask "Where did you get that?" instead of "What's that ugly sensor?" 😄

I've now open-sourced the firmware and electronics side of the project under the MIT license.

The GitHub repo includes the commented ESPHome YAML, ready-to-flash firmware, BOM, wiring, a quick-start flashing guide and Home Assistant automation examples:

[https://github.com/Murco-design/murco-planter](https://github.com/Murco-design/murco-planter)

It runs on an M5Stack AtomS3 Lite with a Grove connection, so no soldering is required. My sons build-tested it too — the goal was to make this something another maker could actually build in an evening, not just a pretty prototype.

I also documented some of the things I learned along the way, including SCD40 self-heating inside an enclosure, calibration, LED brightness and a few ESPHome state-machine mistakes that I wish I'd avoided the first time. 😅

The printable shell and full build guide are available separately for anyone who wants to build it exactly like the one in the photos.

I'm curious where this idea could go next:

**What Home Assistant sensor or device would you love to hide inside something that actually looks good?**

Presence? Temperature? Air quality? Something completely different?

Maybe the planter needs a sequel. 🌱

I built a talking CO₂ sensor with enough WAF to stay in the living room