Some time ago I embarked on a project to build an Arduino-based energy monitor. Many of these have been described on the internet, but I wanted to do it slightly differently. However, after many struggles, trying to get a lot of functionality in a single box (computing running averages, LCD screen with fancy menu system, SD card data logging with RTC time-stamps, record temperature from other sensors connected through RFM12b), I realised that it was getting too complex. Added to that, I short-circuited the VCC and GND, causing the Arduino nano to toast. I managed to remove the nano from the perfboard with a Dremel. After connecting a new Arduino nano I realised it was not the only part that was broke… time to move on!
I decided to take a completely new approach, starting from all things that I had leafed in the process. The RFM12b modules are especially useful, as they allow me to measure and broadcast climate measurements for almost a full year on a single 18650 3.7V LiPo battery. My new design is therefore modular, using RFM12b modules to communicate, and utilises 3.3V where possible. Furthermore, I discovered http://thingspeak.com as a much easier and more user friendly way of data logging and user-interface. I don’t have to walk to the cellar closet to look at the LCD, instead I simply check the current usage on my smartphone.
The new design therefore consists of a single relay station, which receives sensor data on a RFM12b module and forwards it every minute to http://thingspeak.com. Multiple sensor modules are scattered across our house, each recording from a sensor and transmitting a few parameters every minute to the relay station.
Here is a short description of the modules I currently have. In the near future I will post more details, including some photo’s and the source code.
Module 1: Arduino Uno with an Ethershield, connected over i2c to an Arduino pro mini. The pro mini is connected to an RFM12b board and receives data packets from each of the sensor modules. The reason for splitting this over two Arduino’s is that both the Ethershield and RFM12b use SPI. The Ethershield (version 1) does not play nicely with another SPI module. More details are posted here.
Module 5: Arduino pro mini (5V) with a RFM12b and a pair of CNY70 reflective sensors to measure the rotation of the disk of our Ferraris kWh meter and of the last digits of our gas meter. More details are posted here.
Module 6: Arduino pro mini (3.3V) with a RFM12b and a pair of DS18B20 temperature sensors to measure the temperature of the outgoing and returning water of our central heating system. More details are posted here.
I am planning to reimplement the relay module 1 in the near future. I discovered the ESP 8266 wifi module, which is available for around $3.50 on Ebay. Since it has a serial interface, it should not pose any problem combining with an RFM12b.