ADC

1. ADC Overview

ADC (Analog-to-Digital Converter) converts an analog voltage into a digital value. This experiment uses the SAR ADC of the ESP32-S3 to read the voltage on the GPIO4 pin, taking 16 consecutive samples per batch and averaging them, then printing the raw ADC value and the converted voltage (mV) via serial. Averaging filtering effectively suppresses the random noise of a single sample.

Typical application scenarios:

2. Core Concepts

2.1 How the SAR ADC Works

The ESP32-S3 uses a SAR ADC (Successive Approximation Register type). The core idea is binary-search approximation: comparing the input voltage with the DAC output voltage bit by bit from the MSB to the LSB, with 12-bit resolution requiring 12 clock cycles to complete one conversion.

2.2 ADC Attenuation

By default, the ADC of the ESP32-S3 can only measure 0~1.1V. The range can be extended by setting the attenuator:

Choose ATTN_11DB to cover the full 0~3.3V range, which suits most cases.

2.3 ADC Reading and Voltage Conversion

adc.read() returns a 12-bit raw value (0~4095). The conversion formula is:

Voltage formula without attenuation:

Vdata = (data / (2^bitwidth - 1)) × Vref

Voltage formula with attenuation:

xxxxxxxxxx
Vdata = (data / (2^bitwidth - 1)) × Vref / k

The effective precision of the ESP32-S3 ADC is about 11-12 bits; noise in the low bits is normal. This experiment averages 16 samples to reduce noise.

2.4 Averaging Filter

xxxxxxxxxx
sum_val = 0
for i in range(SAMPLE_COUNT):
    sum_val += adc.read()      # 16 consecutive samples
avg_raw = sum_val // SAMPLE_COUNT   # average

Averaging filtering is the simplest digital filter. Averaging 16 samples reduces the standard deviation of random noise to 1/4 of its original value.

2.5 Core API

​x
from machine import ADC, Pin

adc = ADC(Pin(4))            # create the ADC object
adc.atten(ADC.ATTN_11DB)     # set attenuation, range 0~3.3V
val = adc.read()              # read a 12-bit value (0~4095)

3. Hardware Dependencies

In this experiment, you can leave GPIO4 floating to observe the fluctuating reading, or connect an external potentiometer to verify the voltage change.

4. Project Architecture and Flow

xxxxxxxxxx
Script execution (single-file .py)
  │
  ├─ Parameter config: ADC_PIN=4, SAMPLE_COUNT=16, VREF=3300mV
  ├─ adc = ADC(Pin(4))                          // GPIO4 → ADC
  ├─ adc.atten(ADC.ATTN_11DB)                   // range 0~3.3V
  │
  └─ while True:                                // sampling loop (once per second)
       ├─ sum_val = 0                            // clear the accumulator
       ├─ for i in 0..15:                        // take 16 consecutive samples
       │    └─ sum_val += adc.read()             // accumulate the 12-bit values
       ├─ avg_raw = sum_val // 16               // take the average
       ├─ avg_mv = avg_raw * 3300 // 4095      // convert to mV
       ├─ print("ADC_Value=..., Voltage=...mV") // serial output
       └─ sleep_ms(1000)                         // 1s interval

5. Source Code Details

Full source code: 5.Source Code → MicroPython → 1.Basic Peripherals → 6.ADC → 6.ADC.py

5.1 Parameter Configuration and Initialization

xxxxxxxxxx
from machine import ADC, Pin  # ADC and Pin classes
import time                    # delay

# Configuration parameters
ADC_PIN       = 4              # ADC pin (ADC1 CH3)
SAMPLE_COUNT  = 16             # samples per batch
ADC_VREF_MV   = 3300           # reference voltage (mV)
ADC_MAX_COUNT = 4095           # 12-bit full scale

# Init ADC (11dB → 0~3.3V, 12-bit)
adc = ADC(Pin(ADC_PIN))
adc.atten(ADC.ATTN_11DB)

ATTN_11DB extends the range to cover 0~3.3V. adc.read() returns a 12-bit raw value (0~4095).

5.2 Averaged Sampling and Voltage Conversion

xxxxxxxxxx
while True:
    sum_val = 0

    for i in range(SAMPLE_COUNT):
        sum_val += adc.read()       # 12-bit raw value

    avg_raw = sum_val // SAMPLE_COUNT
    avg_mv  = (avg_raw * ADC_VREF_MV) // ADC_MAX_COUNT

    # ADC raw value + voltage (mV)
    print("ADC_Value=%4d, Voltage=%4d mV" % (avg_raw, avg_mv))

    time.sleep_ms(1000)

6. Operation Procedure

6.1 Flashing and Running

Thonny IDE steps: See the 1. Before Development → 3.Thonny IDE chapter.

6.2 Normal Phenomenon

The Thonny Shell prints one line per second:

xxxxxxxxxx
ADC_Value= 636, Voltage= 512 mV
ADC_Value=  83, Voltage=  66 mV
ADC_Value=  75, Voltage=  60 mV
ADC_Value=  71, Voltage=  57 mV
ADC_Value=  77, Voltage=  62 mV
ADC_Value=  85, Voltage=  68 mV
ADC_Value=  95, Voltage=  76 mV
ADC_Value= 102, Voltage=  82 mV
ADC_Value= 103, Voltage=  83 mV
ADC_Value= 101, Voltage=  81 mV
...

• When GPIO4 is floating, the reading fluctuates (normal, pin floating)

  

• Connect 3.3V → the reading is close to 4095, the voltage about 3300mV

Wiring method:

• Connect GND → the reading is close to 0

Wiring method:

6.3 Verification Methods

7. Common Problems