Because life

Touch sensor

https://create.arduino.cc/projecthub/Arca_Ege/how-to-use-a-touch-sensor-81b7f4

The circuit from sensor > arduino
VCC Pin > 5V
GND > GND
OUT > Pin 2
LED pin (short leg (anode) to ground, long leg to Pin 13)

int in = 2; 
int out = 13;  
int state = HIGH;  
int r;           
int p = LOW;    
long time = 0;       
long debounce = 200;
   
void setup()
{
  pinMode(in, INPUT);
  pinMode(out, OUTPUT);
}
void loop()
{
  r = digitalRead(in);
  if (r == HIGH && p == LOW && millis() - time > debounce) {
    if (state == HIGH)
      state = LOW;
    else 
      state = HIGH;
    time = millis();    
  }
  digitalWrite(out, state);
  p = r;
}

Ultrasonic sensor

https://howtomechatronics.com/tutorials/arduino/ultrasonic-sensor-hc-sr04/
https://randomnerdtutorials.com/complete-guide-for-ultrasonic-sensor-hc-sr04/

The circuit from sensor > arduino
+5 > 5V
Trigger > pin 7
Echo > pin 6
GND > GND

const int trigPin = 7; // Trigger Pin of Ultrasonic Sensor
const int echoPin = 6; // Echo Pin of Ultrasonic Sensor

void setup() {
   Serial.begin(9600); // Starting Serial Terminal
}

void loop() {
   long duration, inches, cm;
   pinMode(trigPin, OUTPUT);
   digitalWrite(trigPin, LOW);
   delayMicroseconds(2);
   digitalWrite(trigPin, HIGH);
   delayMicroseconds(10);
   digitalWrite(trigPin, LOW);
   pinMode(echoPin, INPUT);
   duration = pulseIn(echoPin, HIGH);
   inches = microsecondsToInches(duration);
   cm = microsecondsToCentimeters(duration);
   Serial.print(inches);
   Serial.print("in, ");
   Serial.print(cm);
   Serial.print("cm");
   Serial.println();
   delay(100);
}

long microsecondsToInches(long microseconds) {
   return microseconds / 74 / 2;
}

long microsecondsToCentimeters(long microseconds) {
   return microseconds / 29 / 2;
}

Pulse/ Heartbeat Sensor

https://www.hackster.io/Johan_Ha/from-ky-039-to-heart-rate-0abfca — The author converted the signal from the sensor into human-readable beats per minute.

The circuit from sensor > arduino
Signal (S pin) > A0
5V ( + middle pin) > 5V
GND (- pin) > GND

Note: place your finger between the IR led and the light transistor of the sensor. Make sure they are contain in a dark environment to remove noise reflecting from artificial lights. (The reason why the SpO2 probe have opaque protective covers?)

#define samp_siz 4
#define rise_threshold 4

// Pulse Monitor Test Script
int sensorPin = 0;

void setup() {
    Serial.begin(9600);
}

void loop ()
{
    float reads[samp_siz], sum;
    long int now, ptr;
    float last, reader, start;
    float first, second, third, before, print_value;
    bool rising;
    int rise_count;
    int n;
    long int last_beat;

    for (int i = 0; i < samp_siz; i++)
      reads[i] = 0;
    sum = 0;
    ptr = 0;

    while(1)
    {
      // calculate an average of the sensor
      // during a 20 ms period (this will eliminate
      // the 50 Hz noise caused by electric light
      n = 0;
      start = millis();
      reader = 0.;
      do
      {
        reader += analogRead (sensorPin);
        n++;
        now = millis();
      }
      while (now < start + 20);  
      reader /= n;  // we got an average
      
      // Add the newest measurement to an array
      // and subtract the oldest measurement from the array
      // to maintain a sum of last measurements
      sum -= reads[ptr];
      sum += reader;
      reads[ptr] = reader;
      last = sum / samp_siz;
      // now last holds the average of the values in the array

      // check for a rising curve (= a heart beat)
      if (last > before)
      {
        rise_count++;
        if (!rising && rise_count > rise_threshold)
        {
          // Ok, we have detected a rising curve, which implies a heartbeat.
          // Record the time since last beat, keep track of the two previous
          // times (first, second, third) to get a weighed average.
          // The rising flag prevents us from detecting the same rise more than once.
          rising = true;
          first = millis() - last_beat;
          last_beat = millis();

          // Calculate the weighed average of heartbeat rate
          // according to the three last beats
          print_value = 60000. / (0.4 * first + 0.3 * second + 0.3 * third);
          Serial.print(print_value);
          Serial.print('\n');
          third = second;
          second = first;
        }
      }
      else
      {
        // Ok, the curve is falling
        rising = false;
        rise_count = 0;
      }
      before = last;
      ptr++;
      ptr %= samp_siz;
    }
}

Moisture sensor 4 pins to Arduino Uno

A0 > A0 
DO > not used
GND > gnd
VCC > 5V

And in your Arduino code

void setup() {
  // initialize serial communication at the 9600 bits per second
  Serial.begin(9600);

}

void loop() {
  // (A0) Read the input on analog pin 0:
  int sensorValue = analogRead(A0);

  Serial.println(sensorValue);
  delay(100);
}

yeppp! My first project, after waiting approximately 10 days for delivery from China! Bought all the requisites, in twos, and with different sellers, because I was afraid the shipment will break some components or that the particular shipment from the seller is defective. I’m paranoid that way. Heh.

DHT 11 or DHT 22 (3 pins) to Arduino Uno

+out > 5V
middle pin > pin 2
-out > gnd

In your Arduino code, make sure you include library adafruit and DHT sensor for it to work

#include <DHT.h>
#define DHTPIN 2     // Digital pin connected to the DHT sensor
#define DHTTYPE DHT22   // DHT 22 or DHT 11 change DHT accordingly
DHT dht(DHTPIN, DHTTYPE);


void setup() {
  Serial.begin(9600);
  Serial.println(F("DHT22 test!"));

  dht.begin();
}


void loop() {
  // Wait a few seconds between measurements.
  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;
  }

  // Compute heat index in Fahrenheit (the default)
  float hif = dht.computeHeatIndex(f, h);
  // Compute heat index in Celsius (isFahreheit = false)
  float hic = dht.computeHeatIndex(t, h, false);

  Serial.print(F("Humidity: "));
  Serial.print(h);
  Serial.print(F("%  Temperature: "));
  Serial.print(t);
  Serial.print(F("°C "));
  Serial.print(f);
  Serial.print(F("°F  Heat index: "));
  Serial.print(hic);
  Serial.print(F("°C "));
  Serial.print(hif);
  Serial.println(F("°F"));
}

Personal blog to follow my thoughts.

And how to figure things out.