ESP8266 ADC with MicroPython: A Comprehensive Guide

Table of Contents#

1. Fundamental Concepts
   • What is an ADC?
   • How does the ESP8266 ADC work?
   • MicroPython and ESP8266
2. Usage Methods
   • Setting up MicroPython on ESP8266
   • Reading ADC values in MicroPython
3. Common Practices
   • Measuring voltage
   • Building a simple sensor application
4. Best Practices
   • Calibration
   • Handling noise
5. Conclusion
6. References

1. Fundamental Concepts#

What is an ADC?#

An Analog - to - Digital Converter (ADC) is an electronic device that converts continuous analog signals (such as voltage or current) into discrete digital values. In the context of the ESP8266, the ADC can measure analog voltages and represent them as integer values within a certain range.

How does the ESP8266 ADC work?#

The ESP8266 has a single 10 - bit ADC, which means it can represent analog voltages as digital values in the range of 0 to 1023. The ADC on the ESP8266 can measure voltages from 0V to 1V. If you want to measure higher voltages, you need to use a voltage divider circuit.

MicroPython and ESP8266#

MicroPython provides a high - level and user - friendly way to program the ESP8266. It allows developers to write Python code directly on the microcontroller, eliminating the need for complex low - level programming. MicroPython has built - in libraries that make it easy to interact with the ESP8266's hardware, including the ADC.

2. Usage Methods#

Setting up MicroPython on ESP8266#

1. Install esptool.py: This is a tool used to flash the MicroPython firmware onto the ESP8266. You can install it using pip install esptool.
2. Download MicroPython firmware: Go to the official MicroPython website and download the latest firmware for the ESP8266.
3. Flash the firmware: Connect your ESP8266 to your computer via USB. Use the following command to flash the firmware:

esptool.py --port /dev/ttyUSB0 erase_flash
esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash --flash_size=detect 0 esp8266-20230426-v1.20.0.bin

Replace /dev/ttyUSB0 with the actual serial port of your ESP8266 and esp8266 - 20230426 - v1.20.0.bin with the name of the downloaded firmware file.

Reading ADC values in MicroPython#

Here is a simple example of reading ADC values in MicroPython:

import machine
 
# Initialize the ADC
adc = machine.ADC(0)
 
# Read the ADC value
adc_value = adc.read()
print('ADC value:', adc_value)

In this code, we first import the machine module, which provides access to the hardware on the ESP8266. Then we initialize the ADC using machine.ADC(0), where 0 is the ADC pin number on the ESP8266. Finally, we read the ADC value using the read() method and print it.

3. Common Practices#

Measuring voltage#

Since the ESP8266 ADC can only measure voltages from 0V to 1V, we need to use a voltage divider circuit if we want to measure higher voltages. The formula for a voltage divider is:

Here is an example of measuring a voltage using a voltage divider:

import machine
 
# Initialize the ADC
adc = machine.ADC(0)
 
# Define the resistance values of the voltage divider
R1 = 10000  # 10k ohm
R2 = 10000  # 10k ohm
 
# Read the ADC value
adc_value = adc.read()
 
# Convert the ADC value to voltage
voltage = (adc_value / 1023) * 1  # The ADC measures 0 - 1V
actual_voltage = voltage * ((R1 + R2) / R2)
 
print('Actual voltage:', actual_voltage)

Building a simple sensor application#

Let's build a simple light sensor application using a photoresistor. A photoresistor's resistance changes based on the amount of light it is exposed to. When the light intensity increases, the resistance decreases, and vice versa.

import machine
import time
 
# Initialize the ADC
adc = machine.ADC(0)
 
while True:
    # Read the ADC value
    adc_value = adc.read()
 
    # Print the ADC value
    print('Light sensor value:', adc_value)
 
    # Wait for 1 second
    time.sleep(1)

4. Best Practices#

Calibration#

The ADC readings on the ESP8266 may not be very accurate due to manufacturing variations and environmental factors. To improve the accuracy, we can perform calibration. One way to calibrate the ADC is to measure a known voltage and adjust the conversion formula accordingly.

import machine
 
# Initialize the ADC
adc = machine.ADC(0)
 
# Measure a known voltage (e.g., 0.5V)
known_voltage = 0.5
adc_value = adc.read()
 
# Calculate the calibration factor
calibration_factor = known_voltage / ((adc_value / 1023) * 1)
 
# Now use the calibration factor in future measurements
new_adc_value = adc.read()
voltage = ((new_adc_value / 1023) * 1) * calibration_factor
 
print('Calibrated voltage:', voltage)

Handling noise#

ADC readings can be affected by electrical noise. To reduce noise, we can use software filtering techniques such as moving average filtering.

import machine
import time
 
# Initialize the ADC
adc = machine.ADC(0)
 
# Number of samples for moving average
N = 10
samples = [0] * N
index = 0
 
while True:
    # Read the ADC value
    adc_value = adc.read()
 
    # Update the samples list
    samples[index] = adc_value
    index = (index + 1) % N
 
    # Calculate the moving average
    average = sum(samples) / N
 
    # Print the moving average
    print('Filtered ADC value:', average)
 
    # Wait for 1 second
    time.sleep(1)

5. Conclusion#

In this blog post, we have explored the ESP8266 ADC with MicroPython. We covered the fundamental concepts of ADC, how to set up MicroPython on the ESP8266, and how to read ADC values. We also looked at common practices such as measuring voltage and building sensor applications, as well as best practices like calibration and noise handling. By following these guidelines, you can effectively use the ESP8266 ADC with MicroPython to build various IoT applications.

6. References#

• MicroPython official website: https://micropython.org/
• ESP8266 datasheet: https://www.espressif.com/sites/default/files/documentation/0a-esp8266ex_datasheet_en.pdf
• Voltage divider calculator: https://www.allaboutcircuits.com/tools/voltage - divider - calculator/