In two previous posts (this one and this one) I reported on my progress in building a wireless sensor network in my home. I intend to use this network to monitor temperature and humidity in my apartment, particularly in my bathroom. The ventilation there is woefully underpowered, and the resulting humid air encourages growth of some sort of fungus. By monitoring the humidity, I would like to see what the effect is of opening various doors and windows throughout my apartment, looking for the best ventilation strategy.

My plan, so far, was to use an several Arduino Unos with a DHT22 sensor, and have them reporting to a Raspberrypi via a 434MHz transmitter/receiver. Unfortunately, the Uno is very power hungry and gobbles up a 9v battery in several hours. By using a power-saving library it is possible to extend this a bit, but more than a day of running on a 9V battery is out of the question.

After the experiments described in the previous posts, I bought two 4000 mAh 5V power banks and powered the Unos with those. Annoyingly, these power banks shut down if less than a certain amount of current is drawn from them, so I had to actually increase power consumption on the Unos. To add to my misery, the two (identical) powerbanks have a different shutdown threshold and one behaves a bit erratically.

The setup I have now is not at all what I want to have in the long run, but it does enable me to do the experiments related to humidity in my bathroom. For now, that is enough. I will continue working towards some kind of IoT setup in my apartment in a few weeks – without the Unos this time. It has been an interesting learning experience so far!