ADC

1. ADC Overview

ADC (Analog-to-Digital Converter) converts analog voltage into digital values, allowing the MCU to sense the continuous physical world. This experiment reads analog voltage on GPIO4 and prints the ADC raw value (0~4095) and the calculated actual voltage via serial port. Simply use analogRead() to complete the entire process from sampling to quantization.

Typical Application Scenarios:

2. Core Concepts

2.1 ADC Resolution and Reference Voltage

ESP32-S3 SAR ADC has 12-bit resolution:

Output Range: 0 ~ 4095 (2^12 - 1)
Reference Voltage: 3.3V (Vref)

Voltage Conversion Formula:

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voltage = (ADC_value / 4095) × 3.3V

Example: ADC = 2047 → 2047/4095 × 3.3 ≈ 1.65V (half scale)

2.2 analogRead() Internal Flow

1. Select ADC1 controller and corresponding channel

2. Configure sampling time (default ~2.5μs)

3. Start SAR (Successive Approximation Register) ADC conversion

4. Wait for conversion to complete (blocking, ~tens of microseconds)

5. Return 12-bit result from 0~4095

2.3 Input Precautions

• Input range 0 ~ 3.3V, exceeding will damage the GPIO

• To measure higher voltages (such as 5V, 12V), an external resistor divider circuit is required

• Floating ADC pins read random noise - this is normal, not a bug

3. Hardware Dependencies

For testing, leave it floating to observe noise values, or use a Dupont wire to connect GPIO4 to 3.3V/GND to observe full scale/zero.

4. Project Architecture and Flow

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setup()
  ├─ Serial.begin(115200)      // Initialize serial port
  └─ pinMode(4, INPUT)         // Set GPIO4 as analog input

loop()
  ├─ adc_value = analogRead(4) // Read ADC value (0~4095)
  ├─ voltage = adc_value × 3.3 / 4095  // Calculate voltage
  ├─ Serial.printf(...)        // Print results
  └─ delay(1000)               // Sample once per second

5. Source Code

Complete source: Source Code → Arduino → 1.Basic Peripherals → 7.ADC → 7.ADC.ino

5.1 Pin Macro Definition

pinMode(ADC_PIN, INPUT) disables digital output driver and configures as high-impedance analog input.

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#define ADC_PIN 4

5.2 setup() — Initialization

Only need to initialize serial port and pin mode. ADC peripheral is automatically configured by analogRead.

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void setup() {
  Serial.begin(115200);
  pinMode(ADC_PIN, INPUT);
}

Arduino's analogRead automatically completes ADC clock, resolution, and reference voltage configuration on the first call, no manual initialization required.

5.3 loop() — Sampling and Conversion

Read the raw value first, then convert to voltage using the formula. The f suffix in 3.3f indicates float type, avoiding unnecessary double precision overhead.

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void loop() {
  int adc_value = analogRead(ADC_PIN);
  float voltage = (adc_value * 3.3f) / 4095.0f;

  Serial.printf("ADC Value: %4d | Voltage: %.2f V\n", adc_value, voltage);
  delay(1000);
}

%4d is 4-digit right-aligned formatting for neat numeric column alignment. %.2f keeps two decimal places.

6. Operation Flow

6.1 Build and Flash

Arduino flash process: See Arduino → 1. Before Development → 2. Build and Flash.

6.2 Normal Behavior

Open the Serial Monitor (115200 bps), one line printed per second:

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========================================
     ESP32-S3 ADC Experiment Started
========================================
ADC Value:  841 | Voltage: 0.68 V
ADC Value:  237 | Voltage: 0.19 V
ADC Value:  233 | Voltage: 0.19 V
ADC Value:  377 | Voltage: 0.30 V
ADC Value:  157 | Voltage: 0.13 V
ADC Value:  987 | Voltage: 0.80 V
ADC Value:    0 | Voltage: 0.00 V
ADC Value:    0 | Voltage: 0.00 V

Connected to GND state:

Connected to 3V3 state:

Floating state:

6.3 Verification Method

7. Common Issues