9.Input Devices

This week, I took into account three sensors to understand how proximity sensors function for my final project.🛸🛸

Group Task:

Group task

What is an analog input?

Any component, often some type of sensor, that can provide you with a range of values, not just on and off.

To get the formulas in my code I had to analyze the sensor data sheet.

Sensor Data Sheet

Inside this sheet I found important values.

Operating Supply Voltage

Symbol	Rating	Unit	Remark
Vcc	4.5 to 5.5	V	-

🔹 Electro-optical Characteristics

Parameter	Symbol	Conditions	MIN.	TYP.	MAX.	Unit
Measuring distance range	ΔL	(Note 1)	4	-	30	cm
Output terminal voltage	Vo	L = 30 cm (Note 1)	0.25	0.4	0.55	V
Output voltage difference	ΔVo	Output change at L change (30cm → 4cm) (Note 1)	1.95	2.25	2.55	V
Average supply current	Icc	L = 30 cm (Note 1)	-	12	22	mA

• Smaller distance - Higher voltage
• Longer distance - Lower voltage

Voltage and Distance Conversion

In this case I relied on the second graph because it is easier and more accurate to convert voltage at a distance.

The XIAO RP2040 has an analog resolution of 12 bits so its values range from 0 to 4095.

Voltage and Distance

Voltage: I am going to take into account the bits that the ADC of the microcontroller has and I am going to pass it to voltage.

To do this I will use a rule of 3 to convert from analog values of 0 to 4095 to 0 to 3.3v.

Formula for Voltage:

The first formula will be:

Actual voltage in volts (VR):

VR = VADC * (3.3 / 4095)

Now I need a formula for the distance.

For this, I will need the value in volts which will be given to me by the sensor.

To do this, I analyzed the second graph and realized that I had to make another rule of three in which I used a value of the real voltage and the distance it gave.

So I obtained this formula that I was going to use for my code:

X = (12.84 / VR) - 0.42

To check, I calculated each voltage and it did match the voltage on the graph.

So I applied these formulas in my code:

			int voltage = SensorValue * (3.3 / 4095);
			int dis = (12.84 / voltage) - 0.42;
				

programming

Now it's time to program 🛸🛸.

#define pinSensor D2  //Define Sensor Pin
#define pinLeds D0    //Define Leds pin

void setup() {
    Serial.begin(9600);
    pinMode(pinLeds , OUTPUT);  //Define pinLeds as an output
    pinMode(pinSensor , INPUT); //Define pinSensor as an input
}

void loop() {
    delay(500);

    // Read the analog read of pinSensor to calculate the voltage
    float voltaje = analogRead(pinSensor) * (5 / 1023.0);

    // Distance 
    float distance = (12.84 / voltaje) - 0.42;

    Serial.print("Distance(cm):");
    Serial.println(distance);

    if (distance < 15 && distance > 4) {
        digitalWrite(pinLeds , HIGH);
    } else {
        digitalWrite(pinLeds , LOW);
    }
}
    

But when I tried the code, my code didn't give the right distance, so I tried to improve it because I remembered that I only accepted voltages between 4.5V and 5V, but my Xiao only has 3.3V, and that could be the problem. To resolve the problem, I changed the formula in the code: VR = VADC * (5 / 1023.0), as it was originally for a 5V system, and curiously, it gave the correct distance. To check my formula, I tested it on an Arduino, and with this code, it gave the correct distance.The right solution is to use a 5V microcontroller.

2

I decided to analize 2 sensors : Ultrasonic Sensor and PIR sensor

• Supply voltage: 2.8 - 5.5V DC
• Signal voltage: 2.8 - 5.5V (same as supply voltage)
• Detection range: 2-450cm
• Current: < 2mA
• Resolution: 3mm
• Sensor angle: < 15°
• Dimensions: 45 x 20mm

Wiring the Sensor

First, I connected the sensor with the correct pins.

In this case, the sensor has 4 pins:

• Vdc: 5 DC
• Trigger: Input, ultrasonic triggering
• Echo: Output, ultrasound repetition or receiver
• GND: Ground

Formula

In the code, I used the formula:

Distance = speed × time

distance = time * 0.034 / 2;

• time =in microseconds
• 0.034 =time-to-distance conversion (cm/µs)
• / 2 =to calculate the one way only

int TRIG = D9;      // pin for the ultrasonic sensor trigger
int ECO = D8;       // pin for the ultrasonic sensor echo
int LED = D0;       // pin that controls the MOSFET for the LED

long time;        // variable to store echo time
int distance;      // variable to store distance

void setup() {
  pinMode(TRIG, OUTPUT);
  pinMode(ECO, INPUT);
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Send trigger pulse
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  // Read echo time
  time = pulseIn(ECO, HIGH);

  Serial.print("Time: ");
  Serial.println(time);

  // Calculate distance (speed of sound: 340 m/s, divided by 2 and converted to cm)
  distance = time * 0.034 / 2;

  // Show distance on the serial monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // If the distance is less than 20 cm, turn on the LED
  if (distance < 20) {
    digitalWrite(LED, HIGH);
  } else {
    digitalWrite(LED, LOW);
  }

  delay(500); 
}
  

I will now analyze the motion sensor(PIR).

Sensor Specifications

• Power supply voltage: 4.5V - 20V DC
• Detection range: 3 to 7 meters (adjustable)
• Detection angle: <100º (cone)
• Delay time: 5-200 seconds (adjustable)
• Working temperature: -20ºC to 80ºC
• The inputs of a PIR sensor (Passive Infrared) are usually the VCC, GND, and OUT pins.5

// Define MOSFET and sensor variables
const int MosfetPin = D0;
const int SensorPin = D4; 
int statesensor = 0;

// Define inputs and outputs
void setup() {
  pinMode(SensorPin, INPUT);
  pinMode(MosfetPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  statesensor = digitalRead(SensorPin);
  
  // Condition: if the sensor detects a non-zero value, the LEDs will turn on
  if (statesensor == HIGH) {
    digitalWrite(MosfetPin , HIGH);
  }
  // If the sensor does not detect, the MOSFET will turn off
  else digitalWrite(MosfetPin , LOW);
  
  delay(300);  // Small delay
  
  // Print the sensor state (0 or 1)
  Serial.println(statesensor);
}

  

Files

• Pir code
• Ultrasonic Sensor code
• Sharp sensor code

Conclusion🛸🛸

This week was enriching because I learned about analog and digital inputs. It was exciting to see how the sensors could act and provide data.