Receive weather station data with Arduino

A while ago (to be more specific two years ago) I used software defined radio to capture and decode RF signal from the outdoor unit of a weather station. This allowed me to emulate the protocol with an Arduino and a cheap 433.92 MHz transmitter and send my own data to the indoor station. I can make my own units if the original outdoor unit fails. The outdoor unit uses on-off-keying (OOK) and sends pulse distance modulated bits, explained in detail in the linked post.

But what about receiving data from outdoor unit(s) with an Arduino? One can add an ESP8266 to capture temperature and humidity and publish data to MQTT, Home Assistant or other IoT servers. Capturing and analyzing pulse timings of a signal was a daunting task for me. However it turned out to be easier than I thought, using an interrupt routine. In this post, I'll explain all the steps required to make a pulse distance modulation (PDM) decoder.

Send data to weather station over 433.92 MHz

In a previous post I used a software defined radio (SDR) to analyze and decode data transmission over 433.92 MHz of a simple weather station. As I mentioned then, the indoor unit can receive data from up to three outdoor units. I found that outdoor units use basic OOK modulation to send data to indoor unit. Knowing this I can make my own outdoor unit using a 433 MHz transmitter module controlled by an Arduino.

Obviously, I had to use a temperature and humidity sensor such as DHT11, DHT22, AM2302 to get environment parameters. I emulated full original outdoor unit functionality by adding a display and a push button to trigger immediate transmission of data to indoor unit.

Arduino based data transmission device

Decode 433.92 MHz weather station data

I bought a simple weather station, with temperature and humidity display for indoor and up to 3 wireless outdoor sensors (sold with only one though). Unfortunately, the one I got, had a non-functional outdoor sensor. I took it back to the store and got a replacement for the entire product. The outdoor sensor can be hanged on a wall with a small screw, but it can easily fall down.

Given the facts I initially got a broken sensor, the weather station can receive data from up to 3 sensors and because sensors are exposed to outdoor conditions, I decided to analyze the wireless protocol and maybe build my own device which will be able to emulate this kind of sensor. There is no information about wireless protocol of this weather station (sold by Lidl in Europe under the Auriol brand), except the frequency: 433.92 MHz. That was all I needed. And a software defined radio (I used RTL2832U dongle).