ATtiny85 Based Weather Sensor

Short introduction

This project describes how to build more compact temperature and humidity wireless sensor that can transmit the signal to the self made home weather station like this one. Unfortunately this sensor is not compatible with Oregon weather station, despite of it was created using the Oregon protocol documentation. On the other hand, not all Oregon sensors are compatible with Oregon stations. Yet, you can build the weather station using this sensor in several days and the price would be lower than the original Oregon station has.

First of all, the humidity sensor si7021 has shown perfect results, so I recommend this sensor one more time: it has great accuracy, small form-factor and low power consumption.

Second, again we need low power platform that can run on the batteries for a long time. We can run ATtiny85 chip at 1 MHz and put it in sleep mode for about all the time. The power consumption of this system is about 5 micro Amps!

Third, we can use the same software library for sending the signals using Oregon v2.1 protocol. This library is based on the software created by Domonique Pierre, the author of software, emulated Oregon V2.1 protocol.

At the beginning, I tried to use pure library written by Domonique Pierre. Unfortunately, the controller speed is not sufficient to send the data in the time limits required by the protocol. To make the library faster, direct port manipulation was implemented in the new version of the library. In the ATtiny85 controller there is just one output port, B. So you can use the library written for atmega328p IC. There are direct port manipulation functions to send "one" and "zero" signal according by the Oregon protocol that allows to speed-up the signal transmission.

To program our sketch into ATtiny85 you can use Arduino UNO like said here.

Conclusion

I hope, you can enjoy building you own compact weather sensor on ATtiny85. Also, you can investigate this micro controller as well as Arduino. As to a budget of the project, you can evaluate the price of all components:

• ATtiny85 chip - $1, 3 (if you buy one chip)
• Industrial si7021 sensor - $2, 60
• 433 MHz receiver/transmitter kit - $1
• 2xAA battery case - $1
• All small components (capacitors/resistors) - $2

Total: $8. But who can evaluate the fun?