Previously, I used a couple of Arduino Unos to make a sensor network in my home, measuring temperature and humidity. Unfortunately, the Unos use a lot of power and are completely unsuitable for battery-powered operation. Fortunately, there are many other options available and I will discuss two today: the Arduino Pro Mini, and the JeeNode.

Arduino Pro Mini

I bought two 3.3V Minis , aiming for a similar setup as with the Unos. One Mini is the receiver connected to my RaspberryPi, and the second Mini is installed in my bathroom with a DHT22 sensor attached to it. I also changed the wireless modules from the 433MHz modules to 2.4GHz modules, because there were a lot of lost packets with the 433MHz modules, as well as some interference from my neighbour’s wireless doorbell.

Below is a picture of the Mini that is to be installed in my bathroom. The top left shows the battery holder with space for two AA batteries, attached to the Mini with the black and red wires. There are eight wires connecting the 2.4GHz module (bottom) to the Mini (center). At this point, the DHT22 is not attached yet, but it also takes up three pins, and in order to load the software I have to connect a USB-TTL converter to the five pins sticking out of the front of the Mini. Working with this setup is incredible cumbersome, and I quickly got fed up with it. And that is not all, because the Pro Mini still has a LED and a linear regulator eating up a lot of power. It is possible to remove these two elements, but all in all the process is just to involved for my taste. Time to call it quits!

mini_24ghz

JeeNode

After some searching on the internet I came across the JeeNode. It is an Arduino-compatible board with a 868MHz wireless module onboard. The same line of products includes an AA power board with a boost regulator, and a USB-stick type ‘sink’ that I can use as a receiver. In addition, there is a vibrant community and several ready-to-use libraries.

I bought a JeeNode V6, a JeeLink (the sink), and an AA power board and had my network running in no time. Below is a picture of the setup. You can see the wireless module (in green), mounted on the JeeNode without the need for any wires. The power board with the battery is now attached ‘in series’, but can be installed in different ways. The DHT22 is located on the outside of the plastic container.

jeenode

The JeeNode has been running for a while now, and the battery lasts about 6 weeks. I still use the LowPower library, and measure temperature and humidity every 5 minutes. However, if there is no significant change in values compared to the previous reports, then I do not send the measurement (code can be downloaded here). Currently, I’m waiting to see how long the second battery lasts. I should probably buy some device to measure power consumption, so that I can measure how long a battery will last 😉 For now I am reasonable satisfied, although ideally I would like to increase the battery life to several months. More on that later!

Edit: the second experiment also gave a battery life of 6 weeks. I will investigate more later to find out where all the power goes.