This is a simple solution to a simple problem that I’ve been having at work. We have a small, basic server room with air conditioning that is somewhat broken but in a weird way that no one knows how to fix, so far. The air conditioner sometimes decides to shut down with an obscure error code and the room temperature then rises very quickly.
With this project, I wanted to have some sort of temperature measuring at two locations – top and bottom of the rack and have it connected to the network, so that using our information system (and possibly zabbix) we could monitor the temperature, log it, draw pretty charts and most of all send us a message whenever then air conditioner shuts down again (indicated by the rising temperature).
Also the thing should have a small screen showing relevant information on it for times when it can’t be reached through LAN and for a quick glance when I visit the server room. Also it has a small UI to set things up.
For this I used a WEMOS D1 microcontroller and a 16×2 LCD screen. I made the box for it from laser-cut plywood and for probe connections I used 3.5mm audio jacks. Of course after assembly it needs to be calibrated against a known constant temperature (such as boiling water). Calibration values are then put into the device using its web UI.