Input devices

---

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

• Documented what you learned from interfacing an input device(s) to your microcontroller and how the physical property relates to the measured results.
• Documented your design and fabrication process or linked to the board you made in a previous assignment.
• Explained the programming process/es you used.
• Explained any problems you encountered and how you fixed them.
• Included original design files and source code.
• Included a ‘hero shot’ of your board.

Group assignment:

• Probe an input device(s)'s analog and digital signals
• -> A test probe is a physical device used to connect electronic test equipment to a device under test (DUT). To probe means to measure, observe or monitor signals with test probes, for example you could use an oscilliscope or a multimeter.

---

Group Assignment

For this GA Ahmed showed me how to probe an HC-SR04 and a potentiometer using an oscilloscope.
Let's start with the potentiometer:

First, upload this example AnalogInOutSerial code to your board:

							/*
  Analog input, analog output, serial output

  Reads an analog input pin, maps the result to a range from 0 to 255 and uses
  the result to set the pulse width modulation (PWM) of an output pin.
  Also prints the results to the Serial Monitor.

  The circuit:
  - potentiometer connected to analog pin 0.
    Center pin of the potentiometer goes to the analog pin.
    side pins of the potentiometer go to +5V and ground
  - LED connected from digital pin 9 to ground

  created 29 Dec. 2008
  modified 9 Apr 2012
  by Tom Igoe

  This example code is in the public domain.

  http://www.arduino.cc/en/Tutorial/AnalogInOutSerial
*/

// These constants won't change. They're used to give names to the pins used:
const int analogInPin = A0;  // Analog input pin that the potentiometer is attached to
const int analogOutPin = 9; // Analog output pin that the LED is attached to

int sensorValue = 0;        // value read from the pot
int outputValue = 0;        // value output to the PWM (analog out)

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}

void loop() {
  // read the analog in value:
  sensorValue = analogRead(analogInPin);
  // map it to the range of the analog out:
  outputValue = map(sensorValue, 0, 1023, 0, 255);
  // change the analog out value:
  analogWrite(analogOutPin, outputValue);

  // print the results to the Serial Monitor:
  Serial.print("sensor = ");
  Serial.print(sensorValue);
  Serial.print("\t output = ");
  Serial.println(outputValue);

  // wait 2 milliseconds before the next loop for the analog-to-digital
  // converter to settle after the last reading:
  delay(2);
}

						

Moving onto the HC-SR04. First upload the following code to your board. It will initialize the sensor and output the duration with the according distance on the serial monitor.

													
int trigPin = 6;    // Trigger 
int echoPin = 7;    // Echo
long duration, cm, inches;

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

void loop() {
  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  digitalWrite(trigPin, LOW);
  delayMicroseconds(5);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the signal from the sensor: HIGH pulse (duration of the time (in microseconds) 
  // from sending of the ping to reception of its echo off of an object.)
  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);//Reads a pulse (either HIGH or LOW) on a pin. 
          //For example, if value is HIGH, pulseIn() waits
          //for the pin to go from LOW to HIGH, starts timing, 
          //then waits for the pin to go LOW and stops timing.

  // Convert the time into a distance
  cm = (duration/2) / 29.1;     // Divide by 29.1 or multiply by 0.0343 (The speed of sound is: 343m/s = 0.0343 cm/uS = 1/29.1 cm/uS)
 
  
  Serial.print(duration);
  Serial.print("duration, ");
  Serial.print(cm);
  Serial.print("cm");
  Serial.println();
  
  delay(250);
}
						
					

_{End of group assignment}

---

Design and fabrication of the PCB

You can see the documentation for this on my previous weeks' pages: Electronics design & Electronics production

Writing the program

It makes sense to program the microcontroller before connecting other devices, since they might interfere with the upload connection for the code.
The program shown below combines my two codes from Embedded programming / Output devices
It defines the pin connected to the MOSFET's Gate as an output pin as well as all the pins for the HC-SR04 (the input device of this assignment). Everytime the HC-SR04 senses a distance of less than 4cm the pump will activate. The pump gets activated by power that is supplied to the pin, which bridges the connection between the Drain and the Source of the MOSFET, connecting the GND of the pump to the common GND and therefore enabling it to run:

(This code was written with the help of ChatGPT and Rui Santos, https://randomnerdtutorials.com and modified by me.)

int trigPin = 8;    // Trigger 
int echoPin = 7;    // Echo
long duration, cm, inches;
int pumpPin = 9;    // MOSFET Pin for pump control
int minDistance = 4; // Minimum distance for pump activation in cm

void setup() {
	//Serial Port begin
	Serial.begin (9600);
	//Define inputs and outputs
	pinMode(trigPin, OUTPUT);
	pinMode(echoPin, INPUT);
	pinMode(pumpPin, OUTPUT); // Set pumpPin as an output
}

void loop() {
	// The sensor is triggered by a HIGH pulse of 10 or more microseconds.
	// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
	digitalWrite(trigPin, LOW);
	delayMicroseconds(5);
	digitalWrite(trigPin, HIGH);
	delayMicroseconds(10);
	digitalWrite(trigPin, LOW);

	// Read the signal from the sensor: HIGH pulse (duration of the time (in microseconds) 
	// from sending of the ping to reception of its echo off of an object.)
	pinMode(echoPin, INPUT);
	duration = pulseIn(echoPin, HIGH);//Reads a pulse (either HIGH or LOW) on a pin. 
			//For example, if value is HIGH, pulseIn() waits
			//for the pin to go from LOW to HIGH, starts timing, 
			//then waits for the pin to go LOW and stops timing.

	// Convert the time into a distance
	cm = (duration/2) / 29.1;     // Divide by 29.1 or multiply by 0.0343
	inches = (duration/2) / 74;   // Divide by 74 or multiply by 0.0135
	
	Serial.print(inches);
	Serial.print("in, ");
	Serial.print(cm);
	Serial.print("cm");
	Serial.println();
	
	// Activate pump if distance is less than minDistance
	if (cm < minDistance) {
	digitalWrite(pumpPin, HIGH); // Turn on the pump
	} else {
	digitalWrite(pumpPin, LOW); // Turn off the pump
	}
	
	delay(250);
}

Now upload the program to the board as described in the embedded programming assignment.

Connections of the input + output device

Components mentioned:

• 5V regulator LM7805 (Input Voltage: Minimum 7V, Maximum 25V Output Current: 1.5A)
• 12V power adapter
• 12V peristaltic pump

Working HC-SR04 + pump (pumps water when the HC-SR04 gets closer than 4cm to the ground):