Belimo CRA24-B1P Smart Extension

Introduction

Belimo CRA24-B1P is air ventilation controller ("ovladač rekuperace") which does not support smart homes and only way to control it is through push button.

This sucks as you cannot do any automation with it, luckily there is a way to extend it. I found the way how to attach (solder) 7 wires to original controller and control it fully with microcontroller.

This text is covering just case itself, not the electronics. If you are interested in electronics part (how to wire it, what components are needed and looking for firmware) you can find it on my GitHub.

Features

Firmware I wrote is implementing MQTT, thou it can be adjusted to expose directly as HomeKit device if somebody wants that (I prefer MQTT as I have NodeRed backend in which I am exposing it as HomeKit device, it gives you more flexibility and debugging options). Whatever patch you'll chose, you can later control it with Siri and works great! :) 

• Controller can be fully controlled through MQTT
• Controller is sending any change of status through MQTT
• Controller can have default status (when power goes down, you don't need to press manually button to start it up, but you can just set that for example “high” is default status after power goes down and up again …)

Printing instructions

I tried printing PETG, 15% Infill, snug supports everywhere (there are needed for tiny hooks and can be very easily removed …). I used 0.6 mm nozzle with 0.15 mm layer height and 75% print speed on textured bed plate (you can use higher speed on other bed plates or after first layer is finished …).