HX711 and GEDA with MicroPython: A Comprehensive Guide

Table of Contents#

1. Fundamental Concepts
   • HX711 Load Cell Amplifier
   • MicroPython
   • GEDA
2. Prerequisites
3. Usage Methods
   • Hardware Connection
   • MicroPython Code Implementation
4. Common Practices
   • Calibration
   • Error Handling
5. Best Practices
   • Code Optimization
   • Power Management
6. Conclusion
7. References

Fundamental Concepts#

HX711 Load Cell Amplifier#

The HX711 is a precision 24-bit analog-to-digital converter (ADC) designed for weigh scales and industrial control applications to interface directly with a bridge sensor. It has two differential input channels with programmable gain and an on-chip oscillator, which simplifies the design of the weighing system. The HX711 communicates with the microcontroller using a simple serial interface, making it easy to integrate into various projects.

MicroPython#

MicroPython is a lightweight implementation of the Python programming language that is optimized to run on microcontrollers. It provides a high - level programming interface, allowing developers to write code quickly and easily. MicroPython supports a wide range of hardware platforms, including the ESP8266, ESP32, and Raspberry Pi Pico, making it a versatile choice for embedded systems development.

GEDA#

GEDA is a suite of free software tools for electronic design automation. It includes schematic capture, PCB layout, and simulation tools. GEDA can be used to design the hardware circuit for the HX711 and the microcontroller, ensuring that the components are properly connected and the design is optimized for performance.

Prerequisites#

• A microcontroller board supported by MicroPython (e.g., Raspberry Pi Pico, ESP32).
• HX711 load cell amplifier and a load cell.
• Breadboard and jumper wires for prototyping.
• MicroPython firmware installed on the microcontroller.
• A computer with a serial terminal emulator (e.g., PuTTY, Thonny) for uploading and running code.

Usage Methods#

Hardware Connection#

The HX711 has four main pins: VCC, GND, DOUT (data output), and CLK (clock input). The load cell is connected to the HX711's input pins. Here is a typical connection diagram for a Raspberry Pi Pico:

MicroPython Code Implementation#

from machine import Pin
import time
 
class HX711:
    def __init__(self, dout, pd_sck, gain=128):
        self.pSCK = Pin(pd_sck, Pin.OUT)
        self.pOUT = Pin(dout, Pin.IN)
        self.GAIN = 0
        self.OFFSET = 0
        self.SCALE = 1
        self.set_gain(gain)
        time.sleep(1)
 
    def is_ready(self):
        return self.pOUT.value() == 0
 
    def set_gain(self, gain):
        if gain == 128:
            self.GAIN = 1
        elif gain == 64:
            self.GAIN = 3
        elif gain == 32:
            self.GAIN = 2
        self.pSCK.value(0)
        self.read()
 
    def read(self):
        while not self.is_ready():
            pass
        data = 0
        for i in range(24):
            self.pSCK.value(1)
            data = (data << 1) | self.pOUT.value()
            self.pSCK.value(0)
        for i in range(self.GAIN):
            self.pSCK.value(1)
            self.pSCK.value(0)
        if data & 0x800000:
            data -= 0x1000000
        return data
 
    def get_value(self):
        return self.read() - self.OFFSET
 
    def get_units(self):
        return self.get_value() / self.SCALE
 
 
# Example usage
hx = HX711(dout=0, pd_sck=1)
while True:
    value = hx.get_value()
    print(f"Raw value: {value}")
    time.sleep(1)
 
 

Common Practices#

Calibration#

Calibration is essential for accurate weight measurement. To calibrate the HX711, you need to follow these steps:

1. Place a known weight on the load cell.
2. Read the raw value from the HX711.
3. Calculate the scale factor by dividing the known weight by the raw value.
4. Set the scale factor in the code.

# Calibration example
known_weight = 500  # in grams
raw_value = hx.get_value()
scale_factor = known_weight / raw_value
hx.SCALE = scale_factor
 

Error Handling#

When working with the HX711, errors can occur due to electrical noise, improper connections, or other factors. It is important to implement error handling in your code. For example, you can add a timeout when waiting for the HX711 to be ready.

def read_with_timeout(self, timeout=1000):
    start_time = time.ticks_ms()
    while not self.is_ready():
        if time.ticks_diff(time.ticks_ms(), start_time) > timeout:
            raise Exception("HX711 not ready within timeout")
    data = 0
    for i in range(24):
        self.pSCK.value(1)
        data = (data << 1) | self.pOUT.value()
        self.pSCK.value(0)
    for i in range(self.GAIN):
        self.pSCK.value(1)
        self.pSCK.value(0)
    if data & 0x800000:
        data -= 0x1000000
    return data
 

Best Practices#

Code Optimization#

• Minimize the use of blocking functions. For example, instead of using time.sleep() for long periods, use non - blocking timers or interrupts.
• Use efficient data types. For example, use integers instead of floating - point numbers when possible, as floating - point operations are more computationally expensive on microcontrollers.

Power Management#

• Put the microcontroller and the HX711 into sleep mode when not in use to save power.
• Use a low - power load cell and HX711 module if possible.

Conclusion#

The combination of the HX711 load cell amplifier, MicroPython, and GEDA provides a powerful and flexible solution for weight measurement and embedded systems development. By understanding the fundamental concepts, following the usage methods, and implementing common and best practices, you can build accurate and reliable weight measurement systems. Whether you are working on a simple weighing scale or a more complex industrial application, these tools can help you achieve your goals efficiently.

References#

• MicroPython Official Documentation
• HX711 Datasheet
• GEDA Official Website