1. An analog input sensor takes in data from its surroundings and converts it into a value that is represented by a voltage level sent either to an intermediate processor or the microcontroller directly.
2. Analog sensors cannot interface directly with the Pi because all of the Pi's GPIO pins are digital.
3. Two digital interfaces we can use to interface analog sensors with the Pi are I2C and SPI.
4. The two pins (besides ground and power) that an I2C device needs to operate are an SDA (data) pin and an SCL (clock) pin.
5. The sensor object can fire the data event, which means data has been collected, and the change event, which indicates that the data from the sensor has changed.
6. barcli is helpful in processing sensor data because instead of reading hundreds of lines of numbers, you can look at a bar graph and how it changes when you manipulate the sensor.

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