Gautam BoseLucas Ochoa
Published © Apache-2.0

Wash-A-Lot-Bot! A DIY Hand Washing Timer 🧼

An easy way to make a hand-washing timer, using Arduino.

BeginnerFull instructions provided1 hour7,969

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Schematics

Hand Wash Timer - Wiring Diagram

Code

Advanced Timer Code

Arduino
Works the best in more sinks, but may be more difficult to modify and extend.
#include <NewPing.h> // Provides Accurate, Non-blocking sensor data from the Ultrasonic Sensor
#include <Ewma.h>    // Smoothing library - used to remove jitter from sensor data
#include <cppQueue.h> // Queue Library - used to implment mean subttraction so sensor can work in more sinks. 

#include <Servo.h>

#define TRIGGER_PIN  9  // Arduino pin tied to trigger pin on the ultrasonic sensor.
#define ECHO_PIN     10  // Arduino pin tied to echo pin on the ultrasonic sensor.
#define MAX_DISTANCE 200 // Maximum distance we want to ping for (in centimeters). Maximum sensor distance is rated at 400-500cm.


#define IMPLEMENTATION FIFO //Queue implementation as First in First out
#define OVERWRITE      true //Queue will overwrite oldest value when full


int queue_length = 20;
int num_buffer_frames = 50;
int frames_since_launch = 0;
boolean isFirstLaunch = true;
int difference_threshold = 15; //the amount of deviation from the mean that will trigger the countdown. 



NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);
Servo countServo;
Queue window(sizeof(float), queue_length, IMPLEMENTATION, OVERWRITE);

Ewma adcFilter1(0.05); //filter used to smooth sensor data

void setup() {

  Serial.begin(115200);

  //attach pin 7 to servo and sweep it to indicate that the timer is on
  countServo.attach(7);
  countServo.write(180);
  delay(700);
  countServo.write(0);
  delay(700);
  countServo.write(180);

  //start with a clear queue.
  clearQueue();

}

void loop() {
  delay(50); // Wait 50ms between ultrasonic pings (about 20 pings/sec).

  float filtered1 = adcFilter1.filter(sonar.ping_cm()); //get filtered data from the sensor
  float filtered_mean_removed_value = filtered1 - meanZero(filtered1); //subtract the mean so sensor data is centered around zero.
  //This allows the sensor to adjust to different environments and look for change rather than a preset threshold.

  Serial.println(filtered_mean_removed_value);
  if (isFirstLaunch) {
    frames_since_launch++;
  }
  //If the sensor reads something significantly different from what it's normally seeing (the empty sink)
  //we start the countdown!
  if (filtered_mean_removed_value > 15 || filtered_mean_removed_value < -15) {
    if (!isFirstLaunch) {
      countdownServo();
    }

  }

  if (frames_since_launch >= num_buffer_frames) {
    isFirstLaunch = false;
  }

}


//helper function to calculate a moving mean.
int meanZero(float smoothedVal) {

  window.push(&smoothedVal); //push the most recent reading into the queue

  int retval = 0;

  //iterate through the queue and add values to return val
  for (int i = 0; i < queue_length; i++) {
    float for_mean;
    window.peekIdx(&for_mean, i);
    retval = retval + (int)for_mean;
  }

  //calculate the mean and return.
  int mean = retval / queue_length;

  return mean;
}

void clearQueue() {
  for (int i = 0; i < queue_length; i++) {
    float queue_zeroer = 0;
    window.push(&queue_zeroer);
  }
}

//this moves the servo 4.5 degrees every half second
//to smooth out the movemnt (vs 9 degrees every second)
//for 20 seconds.
void countdownServo() {
  Serial.println("Counting down");
  int halfseconds = 40;

  for (int i = halfseconds; i >= 0; i--) {

    countServo.write((int)(i * 4.5));
    delay(500);
  }

  //reset the servo, clear the queue
  countServo.write(180);
  clearQueue();
  delay(700);
  frames_since_launch = 0;
  isFirstLaunch = true;
}

Simple Timer Code

Arduino
Easy to edit and extend, but may cause many false positives.
#include <Servo.h>

const int trigPin = 9;
const int echoPin = 10;

float duration, distance;

//this is the threshold where the sensor will trigger the 
//countdown. If you are getting extra countdowns or the 
//countdown won't start, you may need to adjust this for your sink
int threshold = 200;
Servo countServo;

void setup() {

  Serial.begin(9600);
  
  //attach pin 7 to servo and sweep it to indicate that the timer is on
  countServo.attach(7);
  countServo.write(180);
  delay(700);
  countServo.write(0);
  delay(700);
  countServo.write(180);
}

void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration * .0343) / 2;
  Serial.println(distance);

  if (distance < threshold) {
    countdownServo();
  }
  delay(100);
}



//this moves the servo 4.5 degrees every half second
//to smooth out the movemnt (vs 9 degrees every second)
//for 20 seconds.
void countdownServo() {
  Serial.println("Counting down");
  int halfseconds = 40;

  for (int i = halfseconds; i >= 0; i--) {

    countServo.write((int)(i * 4.5));
    delay(500);
  }

  //reset the servo, clear the queue
  countServo.write(180);
  delay(700);
}

Credits

Gautam Bose

Gautam Bose

0 projects • 0 followers
I'm a creative technologist by trade, but I've been tinkering with software and electronics since I was young. Started with potato cannons.
Lucas Ochoa

Lucas Ochoa

0 projects • 0 followers
Fiver @ Google Creative Lab

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