Week 6

Embedded Programming

Introduction

This week's assignment was to make and test an embedded microcontroller system that I designed. Building on last week's PCB design, I fabricated the VL53L1X distance sensor board, programmed it, and tested its functionality for my hydration monitoring project.

The focus was on the complete embedded systems workflow: from physical board fabrication through firmware development and hardware-software integration testing.

Completed ESP32-S3 XIAO board with VL53L1X sensor
Fully assembled and tested ESP32-S3 board with VL53L1X Time-of-Flight sensor

Making the Board

PCB Fabrication

Using the design from Week 5, I fabricated the board on the Bantam Tools Desktop PCB mill. The milling process took about 30 minutes:

  1. Secured FR1 copper board to milling bed with double-sided tape
  2. Set tool offset using the automatic probing feature
  3. Milled traces with 1/64" flat end mill (0.010" trace width)
  4. Changed to 1/32" end mill for holes and board outline
  5. Carefully removed board and cleaned edges

Component Assembly

Soldering surface-mount components required careful technique:

  • ESP32-S3 XIAO: Hand-soldered using hot air reflow technique
  • VL53L1X sensor: 0.5mm pitch requires fine tip and flux
  • 0603 capacitors: Pre-tinned pads, then placed components
  • Through-hole headers: Standard soldering for programming interface

Videos showing milling process and testing sensor responsiveness

Programming & Testing

Development Environment Setup

I programmed the ESP32-S3 using Arduino IDE 2.0 with the ESP32 board package: 

// Board: XIAO_ESP32S3
// Upload Speed: 921600
// USB Mode: Hardware CDC and JTAG
// Partition Scheme: Default 4MB with spiffs

VL53L1X Sensor Library

I used the Adafruit VL53L1X library which provides a simple I2C interface: 

#include <Adafruit_VL53L1X.h>

Adafruit_VL53L1X vl53 = Adafruit_VL53L1X();

void setup() {
  Wire.begin();
  
  if (!vl53.begin()) {
    Serial.println("Failed to find VL53L1X sensor!");
    while (1) delay(10);
  }
  
  // Set measurement timing budget (higher = more accurate)
  vl53.setTimingBudget(50);  // 50ms
  
  // Start continuous ranging
  vl53.startRanging();
}

void loop() {
  if (vl53.dataReady()) {
    int16_t distance = vl53.distance();
    
    if (distance == -1) {
      Serial.println("Out of range");
    } else {
      Serial.print("Distance: ");
      Serial.print(distance);
      Serial.println(" mm");
    }
    
    vl53.clearInterrupt();
  }
  delay(100);
}

Testing Results

The sensor performed well across its specified range:

  • ✅ Minimum range: 40mm (4cm)
  • ✅ Maximum range: 4000mm (4m)
  • ✅ Accuracy: ±5mm in short range mode
  • ✅ Update rate: Up to 50Hz
  • ✅ Power consumption: ~20mA during ranging

✨ Integration Testing

I tested the sensor's responsiveness by moving objects at different distances. The videos above show the sensor tracking movement in real-time and responding to hand gestures. This validated that the board was ready for integration into the final hydration monitoring system.

Connection to Final Project

While I initially designed this board for distance sensing (measuring water level), I later switched to a load cell-based approach for more accurate weight measurement in the final project. However, the embedded programming skills from this week—I2C communication, sensor calibration, and real-time data processing—directly transferred to programming the HX711 load cell amplifier.