ESP8266 is a very powerful module for building an IoT or WiFi-based project. But since it has only one analog input, you may need to use another microcontroller or circuit to connect multiple sensors and data sources with your ESP8266.
The expander is a 19x14mm board that is powered by a range of 2.7V to 3.6V, features 8 10-bit resolution analog inputs for sensors with an output voltage lower than 3.3V. Allaboutee developed some open source, easy to use libraries and examples:
- VDD – 2.7V to 3.6V (If using with ESP8266 you’ll have to use 3.3V for this pin).
- GND – Ground
- SCL – I2C clock (connect this to GPIO0 of the ESP8266)
- SDA – I2C data (connect this to GPIO2 of the ESP8266)
- A0 -> A7 – Analog inputs (0v to 3.3V)
You can not use two or more boards to have more than 8 analog inputs because the chip’s I2C is factory fixed. If you do not connect a pin to anything, it will be “floating”, that means it’s value is not defined so it can be anything.
This video shows the expander board in action:
“If you were to desire an Arduino based and thus easy to program, WiFi enabled microcontroller, then you could purchase an Arduino WiFi shield for $100+, OR you could instead get an esp8266 w/ breakout board for $6, A 3.3v voltage regulator for $1, the analog input expander $10 and an FTDI to USB 3.3v programmer $3.” – A review by Erol