Analog signals are those signals having values without any restrictions (for example: 1.5 Volts, -5.06 Volts or 2.3 Volts)
Most signals in nature are Analog. That is audio signals are analog, temperature values are analog, speed of a motor is analog.
We need to read analog signals in Arduino to know their exact values to let Arduino take action about it.
For example, if you have a circuit to control temperature in a room, you must be able to read this room temperature to control it.
Also, if you are building a water level controller in a water tank you need to read water level in the tank.
And so on.
In the early days of electronics and Microcontrollers, designers had to put extra ICs called A/D converters (Analog to Digital Converters). That's because Microcontrollers only understand and process digital signals.
But in these days, Microcontrollers come with built in A/D converter which makes design more efficient in code and power usage.
Arduino also comes with internal A/D converters so it can read analog signals with no extra hardware. All you need is writing code(or calling the ready written libraries) for analog input.
This circuit is simply built with Arduino connected to potentiometer to make a variable voltage input(Analog Input) to Arduino.
When Arduino detects a change in analog input, it changes the rate at which the built in LED at pin 13 blinks.
This is the code that runs it:
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