While looking for a WiFi shield for Arduino I discovered the ESP8266.
It comes in many different flavours. The first one, I had, was the ESP8266-01 which is a very cheap WiFi module the Arduino can talk to. But not long and the ESP8266 showed itself as a very powerful chip. 80MHz, 4MB flash and lots of IO ports. And it can be easily programmed with the Arduino IDE, using most of the Arduino libraries. So most of the time there is no need to add an Arduino at all.
Now, most of the time I am using a Adafruit HUZZAH ESP8266 Breakout which is around 10 € and offers me almost everything for most of my projects and sensors. Another very interesting board is Sparkfun ESP8266 Thing which gives you an additional rechargeable battery backup.
So why not use all the time and for all projects an ESP8266 board?
Because sometimes you do not need any connection at all. And WiFi is not very battery friendly. This does not mean that the ESP8266 is not good at sleeping, it is, but waking up e.g. every 60 seconds, powering up the modem, establishing a WiFi connection, getting IP addresses, opening a port to a MQTT server and transferring only a few bytes of payload for temperature or humidity is an awful overhead and consumes too much battery. My sensor, using 2 AA batteries, and transmitting every 60 seconds lasted only 2 weeks. My other experiment with 2 baby batteries and 5 minutes interval now lasts 6 month, but is close to dying now. I found this blog helpful.
So for my battery powered sensors, I will use Atmega328 chips and mysensors.org sketches.
For my „The On Allways Sensor Type TOAST“ I am happy to use the ESP8266. With WiFi and MQTT connection it fits perfectly in any house automation.
So here it is, my „The On Allways Sensor Type TOAST„, enjoy.