Analog-to-Digital Conversion with Arduino

This guide illustrates how to use as best as possible the ADC of Arduino boards, with a focus on the ones based on Atmel ATmega328 microcontroller, such as the popular Arduino UNO. The method to explain is with theoretical references and application examples. In addition, this guide provides a basis for developing projects that are more accurate and improving the existing ones, especially when dealing with acquisition of analog signals.
Reading this guide, you will find answers to questions like the following ones:
─ How many analog signals can an Arduino UNO board acquire "simultaneously"?
─ Is it true that some Arduino boards based on the ATmega328 microcontroller allow two additional single-ended analog inputs?
─ What is the maximum ADC input voltage allowed for an Arduino UNO board? And in the case of an Arduino ZERO?
─ Is it somehow possible to acquire signals larger than the maximum ADC input voltage allowed for an Arduino UNO board?
─ What is the ADC voltage resolution of an Arduino UNO board? And how does the resolution depend on the reference voltage?
─ Can you increase the ADC resolution of an Arduino board?
─ Is it true that the ADC of an Arduino UNO board offers a better resolution than the Raspberry Pi, Particle, Teensy and BeagleBone boards? And compared to boards based on ESP8266EX or ESP32 modules?
─ Is it reasonable to perform voltage measurements with a resolution of microVolts with an Arduino UNO board?
─ How many digits make sense to display the ADC acquisitions?
─ Is it proper to use 1023 or 1024 in the sketch for the voltage conversion formulas?
─ After changing the analog reference voltage with the analogReference() function, how many ADC conversions must be discarded before they can be considered reliable for the acquisition?
─ Is the Arduino UNO ADC more accurate than Leonardo, Yъn or Mega?
─ Using Arduino boards with analog temperature sensors, can you measure temperatures with an accuracy of ±0.1°C?
─ How does the power supply accuracy affect the ADC measurements of an Arduino board?
─ Is it enough to acquire a sample every second to monitor the environment temperature?
─ What is the actual conversion time of an Arduino UNO board?
─ Can you use Arduino UNO board to acquire analog audio signals?
─ What is the oversampling technique?
─ Does it make sense to implement a 13-bit oversampling with an Arduino UNO board?
─ How can you make faster sketches and reduce their size by using the fixed-point arithmetic?