Printed Circuit Board (PCB) Design, Fabrication, and Assembly
Project Working Video

Published October 17, 2023 © GPL3+

XIAO ESP32C3 Portable Weighing Scale, Battery level Indicator

XIAO ESP32C3 Weigh-n-Charge: Portable scale for weight measurement with a built-in battery indicator, ideal for on-the-go use.

BeginnerFull instructions providedOver 1 day489

XIAO ESP32C3 Portable Weighing Scale, Battery level Indicator

Things used in this project

Hardware components

Seeed Studio XIAO ESP32C3

DFRobot Monochrome 0.91”128x32 I2C OLED Display with Chip Pad

Texas Instruments bq27441

SparkFun Load Cell Amplifier - HX711

HX711

Adafruit STEMMA QT

Micro slide switch

Right Angle Tactile Button

Seeed Studio Polymer Lithium Ion Battery - 2200mAh 3.7V

Software apps and online services

Arduino IDE

KiCad

seeed studio PCB/PCBA Services

Hand tools and fabrication machines

Hot Air Station, Industrial

Solder Wire, Lead Free

Soldering iron (generic)

Solder Flux, Soldering

Story

1 / 4

The portable weighing scale is designed with flexibility in mind. It currently has a maximum load capacity of 5 kilograms. However, the load cell can be easily replaced with load cells of different capacities to meet user requirements, whether higher or lower capacity load cells are needed.

Due to the scale being used in an open space, it's important to account for potential variations in measurements. It's expected that there may be fluctuations of 1 to 3 grams in the measured values compared to the actual weight due to environmental factors and conditions. These variations are typical in open environments and are considered in the scale's design and performance specifications.

1 / 2 • Components Identification.

OLED Dispaly info

The portable weighing scale incorporates a Battery Management System (BMS) with integrated Wi-Fi and Bluetooth Low Energy (BLE) connectivity. To ensure precise monitoring of the battery's status and performance, a Battery Fuel Gauge (BFG) based on the BQ27441 chip is employed. A cost-effective solution with an array of features, the seeed Xiao ESP32C3 serves as the project's primary microcontroller.

Block Diagram

The BQ27441 Battery Fuel Gauge provides detailed information about the battery's charging and discharging processes. It accurately measures parameters such as state of charge (SoC), state of health (SoH), and other vital performance metrics. By utilizing the BQ27441, the portable device can maintain an accurate and real-time record of the battery's condition, enhancing the overall reliability and functionality of the product.

The seeed Xiao ESP32C3 module features an internal battery charging system, eliminating the necessity for external circuitry to charge a lithium battery. This integrated charging system streamlines the design and simplifies the power management of devices utilizing the seeed Xiao ESP32C3 module, making it a convenient choice for battery-powered applications.

The device incorporates a sliding switch that allows users to easily power it on and off. Additionally, user-defined switches and LEDs are integrated into the printed circuit board (PCB) to serve as a user interface. These switches and LEDs can be customized and utilized to provide user-friendly controls and status indicators for the device. This user interface design enhances the overall usability and interaction with the portable weighing scale.

The current project does not currently make use of any connectivity features. However, it's important to highlight that Bluetooth Low Energy (BLE) or Wi-Fi connectivity can be easily integrated into the device should such functionality be required in the future. During testing, a 500mAh battery was employed, and it demonstrated a noteworthy battery life of up to 5 hours of continuous operation without the need for recharging. This battery capacity provides a satisfactory amount of usage time, making the device well-suited for various portable applications.

Printed Circuit Board (PCB) Design, Fabrication, and Assembly

The project showcases a tailored PCB (Printed Circuit Board), painstakingly designed with precision using Kicad design software. This meticulous design process takes into account various aspects such as dimensions, shapes, and weight to ensure optimal performance and functionality.

The PCB has been fabricated, and the components have been assembled using Seeed PCB/PCBA services. For information regarding PCB production designs, please feel free to contact me.

1 / 3

Two separate codes are required to create the project.

1. Calibrating the Load Cell Code: Prior to developing the weight scale code, it's imperative to determine the calibration factor. The calibration factor is essential for ensuring accurate results, as it eliminates the need for users to spend excessive time fine-tuning the measurements.

Calibration Factor = (Reading )/ (Known Weight Placed)

In the context of calibrating the Load Cell Code, the term "Reading" typically refers to the numerical value or measurement displayed on the screen when the code is executed. This "Reading" represents the output of the load cell sensor and indicates the weight or force being measured by the scale. Users can use this reading to calibrate the scale and ensure accurate weight measurements.

"Known Weight Placed" refers to the weight that is placed on the system or scale during the monitoring process. This known weight serves as a reference or standard for calibration and is used to verify the accuracy of the scale's measurements when objects of known weight are placed on it.

Example: The code displays a reading of 20105 when a 50-gram known weight is placed on the sensor.

Calibration Factor = 20105/50

The Calibration Factor is 402.1

2. Weight Measuring code: after the calibration factor is calculated this code is executed as the main code, by including the calibration"Weight Measuring Code: After calculating the calibration factor, this code is executed as the main program, incorporating the calibration factor details." factor details in the code.

Project Working Video

Schematics

Code

#include <SparkFunBQ27441.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include "HX711.h"
#define calibration_factor 402.1 //sensor2
#define LOADCELL_DOUT_PIN  D0
#define LOADCELL_SCK_PIN  D1
#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 32 // OLED display height, in pixels
int led = D10;
// Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)
#define OLED_RESET     4// Reset pin # (or -1 if sharing Arduino reset pin)
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// Set BATTERY_CAPACITY to the design capacity of your battery.
const unsigned int BATTERY_CAPACITY = 500; // e.g. 850mAh battery
HX711 scale;


void setupBQ27441(void)
{
  lipo.begin();
  // Use lipo.begin() to initialize the BQ27441-G1A and confirm that it's
  // connected and communicating.
  if (!lipo.begin()) // begin() will return true if communication is successful
  {
    // If communication fails, print an error message and loop forever.
    Serial.println("Error: Unable to communicate with BQ27441.");
    Serial.println("  Check wiring and try again.");
    Serial.println("  (Battery must be plugged into Battery Babysitter!)");
    while (1) ;
  }

  Serial.println("Connected to BQ27441!");
  lipo.setCapacity(BATTERY_CAPACITY);
}

void printBatteryStats()
{
  // Read battery stats from the BQ27441-G1A
  unsigned int soc = lipo.soc();  // Read state-of-charge (%)
  unsigned int volts = lipo.voltage(); // Read battery voltage (mV)
  int current = lipo.current(AVG); // Read average current (mA)
  unsigned int fullCapacity = lipo.capacity(FULL); // Read full capacity (mAh)
  unsigned int capacity = lipo.capacity(REMAIN); // Read remaining capacity (mAh)
  int power = lipo.power(); // Read average power draw (mW)
  int health = lipo.soh(); // Read state-of-health (%)

  // Now print out those values:
  String toPrint = String(soc) + "% | ";
  toPrint += String(volts) + " mV | ";
  toPrint += String(current) + " mA | ";
  toPrint += String(capacity) + " / ";
  toPrint += String(fullCapacity) + " mAh | ";
  toPrint += String(power) + " mW | ";
  toPrint += String(health) + "%";

  display.clearDisplay();
  display.setTextSize(1);             // Normal 1:1 pixel scale
  display.setTextColor(SSD1306_WHITE);        // Draw white text
  display.setCursor(0, 15);
  display.print("Battery Level:");
  display.print(soc);
  display.print("% ");
  display.setCursor(0, 25);
  display.print("Battery Volt:");
  display.print(volts);
  display.print("mV");

  display.setCursor(30, 0);  
  display.print("Weight:");// Start at top-left corner
  display.print(scale.get_units(), 1);
  display.print(" g");
  display.display();      // Show initial text
  display.display();      // Show initial text
  Serial.println(toPrint);
  Serial.print("Reading: ");
  Serial.print(scale.get_units(), 1);//scale.get_units() returns a float
  Serial.print(" Grams"); //You can change this to kg but you'll need to refactor the calibration_factor
  Serial.println();

  
}

void setup()
{
  pinMode(led, OUTPUT);
  Serial.begin(9600);
  setupBQ27441();
  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
  scale.set_scale(calibration_factor); //This value is obtained by using the SparkFun_HX711_Calibration sketch
  Serial.println("Readings:");
  scale.tare(); //Assuming there is no weight on the scale at start up, reset the scale to 0
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // Address 0x3C for 128x32
    Serial.println(F("SSD1306 allocation failed"));
    for (;;); // Don't proceed, loop forever
  }
  display.display();
  delay(2000); // Pause for 2 seconds
  display.clearDisplay();
}

void loop()
{
  printBatteryStats();
}

// Calibrating the load cell
#include "HX711.h"

// HX711 circuit wiring
const int LOADCELL_DOUT_PIN = D0;
const int LOADCELL_SCK_PIN = D1;

HX711 scale;

void setup() {
  Serial.begin(9600);
  scale.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
}

void loop() {

  if (scale.is_ready()) {
    scale.set_scale();    
    Serial.println("Tare... remove any weights from the scale.");
    delay(5000);
    scale.tare();
    Serial.println("Tare done...");
    Serial.print("Place a known weight on the scale...");
    delay(5000);
    long reading = scale.get_units(10);
    Serial.print("Result: ");
    Serial.println(reading);
  } 
  else {
    Serial.println("HX711 not found.");
  }
  delay(1000);
}

//calibration factor will be the (reading)/(known weight)

Credits

vinay y.n

25 projects • 40 followers

An electronic product engineer with 8 years of experience in the field. The passion for electronics began as a hobby 11 years ago.

XIAO ESP32C3 Portable Weighing Scale, Battery level Indicator