“In this article is shown how to build your own wireless weather sensor compatible with Oregon weather station using compact attiny85 micro controller. You can buy spare Oregon sensor THGN123N for about $20 or you can build your own wireless sensor that implements Oregon protocol V2.1 for about $9 and have fun! The main component of the sensor is an accurate temperature/humidity sensor that can report the weather condition with high precision (about 0.5 degree of centegrees). The si7021 sensor has shown perfect results, so I recommend this sensor one more time: it has great accuracy, small form-factor and low power consumption. Also, we need mobile platform with low power requirements that can run on the batteries for a long time. The sensor firmware is small and can easily fit into attiny85 micro controller memory. The power consumption of the attiny85 running at 1MHz in sleep mode is about 4 micro Amps! And the last, we need the software library for sending the signals using appropriate protocol. Happily, there is the software created by Domonique Pierre, emulated Oregon V2.1 protocol, that we can reuse.”