9. Input Devices

This week i explored on this two input devices as they are related to my final project.This helped me to know the pin outs of these sensors and the connections with XIAO SAMD21 PCB fabricated board.PIR sensor was mainly used for motion detection.

Assignments for week 9:

1. Group Assignment

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

2. Individual Assignment

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

1. Group Assignment.

Group Assignment link is here

Learnings outcomes from the group assignment:

I haved learned the digital and analog signals displayed by the logic analyzer and oscilloscope where I2C channels were used to interface.This group assignment will help me debugg my program and observe the working of the input devices and compare among the sensors.

2. Individual Assignment.

1) VL53L1X Distance sensor with Arduino IDE.

I have decided to work on VL53L1X Distance sensor.

About VL53L1X Distance Sensor, its specifications and Pinouts

This sensor is a Time-of-Flight ranging module with its range accuracy upto 4 meters and has fast ranging frequency upto 50 Hz.It is controlled through I2C interface with lower power consumption.The brand available was of Wavshare

Specifications

• Operating voltage: 3.3V/5V
• Dimension: 20mm × 24mm
• Mounting holes size: 2.0mm
• anging distance: 40 ~ 4000mm
• Ranging accuracy: ±5%
• Ranging time (min): 20ms (short distance mode), 33ms (medium/long distance mode)
• Field of view: 27°
• Laser wavelength: 940nm
• Operating temperature: -20 ~ 80°C

Pinouts of VL53L1X distance sensor:

• VCC: 3.3V/5V power input
• GND: ground
• SDA: I2C data pin
• SCL: I2C clock pin
• SHUT: shutdown control, connects to IO pin
• INT: interrupt output, connects to IO pin

Here is our reference about VL53L1X Distance sensor

Workflow Using VL53L1X distance sensor.

1. Adding library for VL53L1X distance sensor in Arduino IDE.

For the VL53L1X distance sensor I have referred its library from the Input devices class since the Arduino IDE does not containg library for this sensor.

I had copied the link address and pasted under “preferences”.

After adding the library package, searched for it under the library manager and installed it.

The libabry contains its examples so i haved choosed an example code to try the sensor.

I clicked on ‘Examples’ under ‘Files’, then choosed ‘VL53L1X’ and finally clicked to choose ‘ContinuousWithDetails’ as shown below.

This was the code i have choosed for programming.

#include <Wire.h>
#include <VL53L1X.h>

VL53L1X sensor;

void setup()
{
  while (!Serial) {}
  Serial.begin(115200);
  Wire.begin();
  Wire.setClock(400000); // use 400 kHz I2C

  sensor.setTimeout(500);
  if (!sensor.init())
  {
    Serial.println("Failed to detect and initialize sensor!");
    while (1);
  }

  // Use long distance mode and allow up to 50000 us (50 ms) for a measurement.
  // You can change these settings to adjust the performance of the sensor, but
  // the minimum timing budget is 20 ms for short distance mode and 33 ms for
  // medium and long distance modes. See the VL53L1X datasheet for more
  // information on range and timing limits.
  sensor.setDistanceMode(VL53L1X::Long);
  sensor.setMeasurementTimingBudget(50000);

  // Start continuous readings at a rate of one measurement every 50 ms (the
  // inter-measurement period). This period should be at least as long as the
  // timing budget.
  sensor.startContinuous(50);
}

void loop()
{
  sensor.read();

  Serial.print("range: ");
  Serial.print(sensor.ranging_data.range_mm);
  Serial.print("\tstatus: ");
  Serial.print(VL53L1X::rangeStatusToString(sensor.ranging_data.range_status));
  Serial.print("\tpeak signal: ");
  Serial.print(sensor.ranging_data.peak_signal_count_rate_MCPS);
  Serial.print("\tambient: ");
  Serial.print(sensor.ranging_data.ambient_count_rate_MCPS);

  Serial.println();
}

Above code explanation.

The code above explains that the VL53L1X distance sensor get interface with my fabricated board of XIAO SAMD21.The sensor measures the distance and calculates the time it takes to reflect off an object.The code initializes the sensor which let to configure its settings and continuously reading the distance data and finally gets printed to the serial monitor.

The detailed description of code is below.

#include <Wire.h>
#include <VL53L1X.h>

The ‘Wire.h’ is the library required for 12C communication for VL53L1X sensor to communicate with XIAO SAMD21 MCU.

The ‘VL53L1X.h’ mean the library for VL53L1X distance sensor that will function to interface.

void setup()
{
  while (!Serial) {}
  Serial.begin(115200);
  Wire.begin();
  Wire.setClock(400000); // use 400 kHz I2C

The above setup function explains that serial port gets ready and it initializes the serial communication at baud rate of 115200 which allows the data to be sent to serial monitor.The I2C clock speed is set to 400 kHz.

sensor.setTimeout(500);
  if (!sensor.init())
  {
    Serial.println("Failed to detect and initialize sensor!");
    while (1);
  }```

  This means that the timeout for sensor is set with 500 milliseconds and initializes the sensor.

The sensor is configured to long distance mode upto 4 meters which takes 50 milliseconds to take each measurement.The distance is measured continuously.

void loop() { sensor.read();

Serial.print(“range: “); Serial.print(sensor.ranging_data.range_mm); Serial.print(“\tstatus: “); Serial.print(VL53L1X::rangeStatusToString(sensor.ranging_data.range_status)); Serial.print(“\tpeak signal: “); Serial.print(sensor.ranging_data.peak_signal_count_rate_MCPS); Serial.print(“\tambient: “); Serial.print(sensor.ranging_data.ambient_count_rate_MCPS);

Serial.println(); } ``

The loop function reads a new measurement from sensor in mm and prints to serial monitor.The status of range measurements are converted to readable and printed to serial monitor.

1. Connections of Sensor pins with a PCB board fabricated.

I have connected the SDA pin of sensor to the SDA pin of PCB board, followed by SCL to SCL, VCC to 5V of board, and GND to GND.We have used my fabricated PCB board of week 8

Then followed by compiling and uploading my program into Arduino IDE after selecting board and port. After that clicked on “Serial Monitor”.

Our connection worked showing distances as we move the sensor.

2) AM321 PIR sensor with XIAO SAMD21 board.

About PIR sensor

PIR sensors are used to detect motion within the range.These sensors are small, cheap, low power and easy to use and do not wear out.They are commonly referred as “Passive Infrared” or IR motion sensors.

More details can be found from my reference link about PIR sensor.

I have used AM321 PIR sensor to test with my PCB board fabricated.

Pinouts of AM321 PIR sensor.

• VCC(3.3V/5V) for power supply.
• GND
• OUT(Signal) as output pin.

Workflow for PIR sensor AM321 with XIAO SAMD21 board.

I have referred the codes from chatGPT where i made slight changes.

Next i did the connections for PIR sensor with my board using breadboard, jumper wires and USB cable.Here are the connection details.

pin outs of my PCB board with XIAO SAMD21

• VCC of AM321 PIR sensor to 3.3V of my PCB board
• GND of PIR sensor to GND of my PCB board.
• OUT(Signal) of PIR sensor to GPIO03 OR D3

AM321 PIR sensor work with Seed Studio XIAO SAMD21 for simple signals without library as its signals can be read using “digitalRead()”

Then, i opened Arduino IDE and selected new sketch.I have pasted the code and changed output pin for PIR sensor to D3.

This is the code from chatGPT:

#define PIR_PIN D3  // AM321 PIR sensor output connected to D3

void setup() {
    pinMode(PIR_PIN, INPUT);
    Serial.begin(115200);
}

void loop() {
    static unsigned long motionStart = 0;

    if (digitalRead(PIR_PIN) == HIGH) {
        if (motionStart == 0) {
            motionStart = millis();  // Start timing motion
        }
    } else {
        if (motionStart > 0) {
            unsigned long motionDuration = millis() - motionStart;
            motionStart = 0;  // Reset timer

            if (motionDuration < 1000) {  // Assume <50 cm movement
                Serial.println("Motion detected within 50cm!");
            }
        }
    }
    delay(100);  // Adjust sensitivity
}

From the above code for PIR sensor, the PIR sensor was defined initially as ‘#define PIR _Pin D3’ where i changed pin to D3.For function ‘Void Setup() {‘, it means PIR sensor was configured as input with ‘PinMode(PIR_PIN, INPUT) and serial communication started with 115200 baud rate. Initially motion started with 0 millisecond.Motion detected within 20cm range after each motion stops with a 1 second.

Then, I have connected my board set up above via USB to my computer and proceed to add board and port under the “Tools”.

Now clicked to compile and clicked upload.

I followed to clicked on serial monitor to detect the motion for my connection and it displayed the motion detected.

My Learning outcomes from this individual assignment.

This week i have learned some of the input devices with their connections with the fabricated PCB boards.I have also observed the digital and analog signals interpreted on the I2C channels of logic analyzer and oscilloscope.The Logic analyzer helped to observe the communication between the input sensors and the board used.

Disclaimer :I have used codes for VL53L1X distance sensor from the examples from Arduino IDE and for PIR sensor from chatGPT.However, i have summarized my understanding at end of each workflow.

Program Code Files

1. Code file for VL53L1X distance sensor is here

2. Code file for PIR motion sensor is here