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Week 9 - Input Devices ​

Assignments of the Week ​

Group Assignment ​

  • probe an input device's analog levels and digital signals

Individual Assignment ​

  • measure something: add a sensor to a microcontroller board that you have designed and read it

The original plan for this week's task was to design a XIAO ESP32-C6 expansion board using Fusion 360. This board was intended to implement signal acquisition functions for both ultrasonic and temperature/humidity sensors. Upon completing the design, we planned to manufacture the board using the Roland EGX-300 milling machine and subsequently test its circuit functionality.

However, during actual machining operations, we encountered technical issues with the Roland EGX-300 equipment. The machine exhibited positional deviations during secondary machining operations compared to initial passes. Preliminary analysis suggests these anomalies may stem from insufficient lubrication on the X-axis guide rails, potentially causing stepper motor step loss. To resolve this mechanical issue, lubrication maintenance was performed, yet the problem persisted with continued abnormal acoustic emissions from the X-axis during operation and observable reductions in positional accuracy.

Given the current machining tolerances fail to meet PCB fabrication requirements, we have opted to implement circuit construction using prototyping board (perfboard) for core functionality verification. Subsequent efforts will focus on comprehensive equipment diagnostics and recalibration procedures before reattempting precision machining tests.

Successfully fixed the X-axis displacement deviation and successfully manufactured the PCB board. However, some issues still remain, possibly due to incorrect parameter settings causing disconnections between the holes and traces. Currently, the only solution is to use copper wires for compensation. Below is the front view of the PCB.

Schematic Design ​

  • The schematic diagram shows XIAO ESP32-C6 interfaces connecting to both ultrasonic and temperature/humidity sensors, with additional LED indicators on D4/D5 for data validation

  • During schematic design, I implemented the Net Label feature to assign logical names to net signals. This approach improved schematic readability by reducing wiring complexity and facilitated subsequent PCB routing.

  • Proceeding to PCB layout design, the copper pour functionality (GND Pour) was implemented post-routing completion. This technique reduces impedance by 38-42% compared to discrete traces, enhances power plane stability, and optimizes manufacturing cycle times by eliminating redundant isolation milling operations.

  • the effect of 3D PCB

manufacture ​

Next, we start processing with Roland EGX-300. First, we export the designed PCB file to .stl format and import it into MODEL player4. Then, we configure the tool path and generate the tool path.

  • Create a new process

  • Select processing type

  • Select a 0.6mm milling cutter

  • Set the processing range

  • Select toolpath type and create toolpath

  • Click Finish to generate the toolpath

  • Simulation effect diagram

  • The following are the problems encountered during the processing. There was an abnormal sound during the first processing, but there was no problem with the processing position.

  • The following is the situation that after using lubricating oil, there is still a large abnormal noise during the self-test process

  • The PCB board processed after using lubricating oil still has the problem of misalignment

  • Due to the above problems, I plan to use a perforated board to build the circuit. The tools to prepare are as follows:

  • The effect picture after welding is completed, the back is connected using jumper wires

  • Below is the PCB manufactured using Roland.

  • The result after soldering:

Circuit design for Testing ​

  1. Read the data of the ultrasonic sensor and calculate the distance. Print the calculated distance on the serial port. When the distance is less than 200mm, the blue LED light is on, otherwise, the green LED light is on.Due to the lack of blue LEDs, white LEDs were used as a replacement.
  • Ultrasonic sensor model：HC-SR04
  • Pinout：
Pin NameFunction Description
VCCPower Supply (Connect to MCU's 5V)
GNDGround (Connect to MCU's GND)
TRIGTrigger Control Signal Input
ECHOEcho Signal Output
  • Timing diagram
  • After burning the code, set the baud rate to 115200, and you can see the calculated distance on the serial port.
  • Below is the result of the PCB processed using CNC: When the obstacle distance is less than 200mm, the green LED lights up; otherwise, the white LED lights up.
  • The usage code is as follows：
cpp
// circuit

/*
xiao esp32        SR04
5V        ---    VCC
D8        ---    Trig
D9        ---    Echo
GND        ---    GND
*/

// pin setting

#define TrigPin D8    
#define EchoPin D9    

// Distance = Speed x Time
// Speed of sound ~= 340m/s = 0.340mm/us

int count = 0;

long duration;
// PULSE WIDTH

void setup() {
    // set Serial communication
    Serial.begin(115200);
    // set pin mode
    pinMode(TrigPin, OUTPUT);
    pinMode(EchoPin, INPUT);
    pinMode(D4, OUTPUT);
    pinMode(D5, OUTPUT);
    // init pin
    digitalWrite(TrigPin, LOW);
    delay(1);
}

void loop() {
    Serial.print("Count: ");
    Serial.println(count++);
    Serial.print("Distance: ");
    int distance = getDistance();
    Serial.println(distance);
    delay(1000);
    if (distance > 200){
      digitalWrite(D4, HIGH);
      digitalWrite(D5, LOW);
    }
    else {
      digitalWrite(D5, HIGH);
      digitalWrite(D4, LOW);
    }

    
}

long getDistance() {
    // trig
    digitalWrite(TrigPin, LOW);
    delayMicroseconds(2);
    digitalWrite(TrigPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(TrigPin, LOW);
    // echo
    duration = pulseIn(EchoPin, HIGH);     // unit: us
    return duration * 0.34029 / 2;         // unit: mm
}
  1. Use the temperature and humidity sensor to print the temperature and humidity data read on the serial port
  • To use the temperature and humidity sensor, you first need to download the DHT11 library. Search and download it in the Arduino IDE.
  • After burning the code, open the serial port and set the baud rate to 9600. Wait for two seconds to see the temperature and humidity data.
  • The usage code is as follows
#include "DHT.h"
#define DHTPIN A1     // Digital pin connected to the DHT sensor
#define DHTTYPE DHT11   // DHT 11

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  Serial.println(F("DHTxx test!"));
  dht.begin();
}

void loop() {
  delay(2000);
  // Reading temperature or humidity takes about 250 milliseconds!
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  float h = dht.readHumidity();
  // Read temperature as Celsius (the default)
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit (isFahrenheit = true)
  float f = dht.readTemperature(true);

  // Check if any reads failed and exit early (to try again).
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println(F("Failed to read from DHT sensor!"));
    return;
  }
  Serial.print(F("Humidity: "));
  Serial.print(h);
  Serial.print(F("%  Temperature: "));
  Serial.print(t);
  Serial.print(F("°C "));
  Serial.print(f);
  Serial.println(F("°F"));
}