ADC Basics: Analog to Digital Conversion

What is Analog to Digital Conversion?

Analog signals are continuous in nature and represent real-world phenomena like temperature or sound. Digital signals, on the other hand, are discrete and represented by binary numbers (0s and 1s). An ADC bridges the gap by converting continuous analog signals into digital values that microcontrollers can process.

How Does ADC Work?

An ADC samples an analog input signal at regular intervals, measures the signal's amplitude, and quantizes it into discrete digital values. The result is typically represented as a binary number, with the precision determined by the ADC's resolution.

Key ADC Terminologies

• Resolution: The number of unique values the ADC can output, determined by its bit depth. For example, a 10-bit ADC has 1024 levels (2¹⁰ = 1024).
• Sampling Rate: How often the ADC samples the analog signal per second, typically measured in samples per second (SPS).
• Reference Voltage (V_ref): The maximum voltage the ADC can measure. Input voltages are scaled relative to this value.
• Quantization Error: The difference between the actual analog value and its digital representation due to the finite resolution of the ADC.

ADC Process Flow

1. An analog signal is applied to the ADC input.
2. The ADC samples the signal at specific intervals.
3. The sampled signal is quantized to a digital value based on the ADC resolution and reference voltage.
4. The digital output is then sent to the microcontroller for further processing.

Example: Reading Analog Values in Arduino

The analogRead() function in Arduino is used to read analog inputs from a pin. Below is a simple example:

// Basic ADC reading in Arduino
int sensorPin = A0;  // Analog pin connected to the sensor
int sensorValue;     // Variable to store the sensor value

void setup() {
  Serial.begin(9600);  // Start serial communication
}

void loop() {
  sensorValue = analogRead(sensorPin);  // Read the analog input
  Serial.println(sensorValue);          // Print the value to the Serial Monitor
  delay(500);                           // Wait for half a second
}
            

Interpreting the Results

The analog value returned by analogRead() ranges from 0 to 1023 for a 10-bit ADC. You can calculate the corresponding input voltage using the following formula:

Input Voltage (V) = ADC Value × (V_ref / ADC Resolution)

For example, if the reference voltage is 5V:

Input Voltage = 512 × (5 / 1023) ≈ 2.5V

Conclusion

ADC enables microcontrollers to interpret real-world analog signals by converting them into digital values. Understanding ADC fundamentals is crucial for designing systems that interact with physical environments, such as sensor-based applications.