Editorial Solution

If we analyze the task carefully,
- We need a varying voltage source. For that, we will use a potentiometer from the range of 1k to 10k Ω.
- To print voltage we will use Serial Monitor.
The circuit is connected as shown in the diagram below.

Connection

Let us write the code for this voltmeter setup. It is very straightforward :
- Read analog value
- Convert analog value to voltage
- Print on Serial monitor

Code

// Pin for analog input
const int analogPin = A0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  // Read the raw ADC value (10-bit resolution: 0 to 1023)
  int adcValue = analogRead(analogPin);
  
  // Convert the ADC value to voltage
  // 5V reference, voltage = (adcValue * 5.0) / 1023
  float voltage = adcValue * (5.0 / 1023.0);

  // Print the ADC value and corresponding voltage
  Serial.print("ADC Value: ");
  Serial.print(adcValue);
  Serial.print(" | Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  
  // Wait for a short time before taking another reading
  delay(500);  // 500ms delay
}

Code explanation

We will be using an A0 pin for voltage measurement.
The code performs the following tasks, which are listed with their respective functions:
- analogRead(analogPin): reads ADC value.
- float voltage = adcValue * (5.0 / 1023.0) : converts ADC_value to voltage.
- Serial.print: print ADC_value and Voltage.

Output

The circuit connection is as follows

The output of the voltmeter readings is as follows

As we can see in the video, the Voltage change is successfully detected and printed on the Serial monitor.

Limitations

Our voltmeter can measure with the accuracy of +- 4.88 mV. To improve voltmeter accuracy we need to use ADC with higher resolution.
The potentiometer output pin produces 0V (GND); it is not exactly 0V. Some current flows and ADC readings randomly shift from 0 to 1 (around 5 mV fluctuations).

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