The quest for a Home Monitoring System : Part 3
Sensor Modules for data acquisition
The initial sensor module was done with an Arduino + DS18B20 sensor and a ENC28J60 ethernet chip. It was pretty fast to build a prototype that would send data via ethernet to a server running a LAMP stack.
However, since I want to have sensors trough out the house (including the exterior), it became a problem since I’m unable to pass an Ethernet cable everywhere I might need a sensor module installed.
The cheapest to add wifi capabilities to an arduino based system would be to add an ESP8622 wifi module :
- They are low priced – around 1,7€ a piece on ebay.
- Answer to AT commands via serial communication (thus an arduino board could simply send AT commands to the module with the data).
But upon more reading, it was also noted that the ESP8266 could be used as a stand alone module, without the arduino hardware. This helps drive the cost and assembly complexity of each module down further. A major plus was the fact that the arduino IDE can be used with the ESP8266, work with most libraries already included, without changes to software development workflow.
And since the ESP8266 supports I2C and 1 wire data buses, any sensor supporting those protocols can be added to a ESP8266 module.
Sensor module variants
A total of 3 variants of the ESP8266 based sensor module, as of 17th February, were built:
- A module only using a temperature sensor (the DS18B20), with no RTC on board. Exists in breadboard form only and it is currently in use.
- A module using both a DHT22 humidity and temperature sensor, and also a DS18B20 sensor. Also without RTC support. Module was disassembled and parts used on the PCB version 1.0.
- A module using a DHT22 humidity and temperature sensor, with a DS1337 RTC, as used on my Nixie Clock. This version was built on a PCB designed in KICAD, and it is currently in use.