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Physical Computing Week 2: Tuesday Labs

Quiz 2:

1. An analog sensor physically outputs variable voltage and allows a microcontroller to read a range of values. An example of an analog sensor is a photocell light sensor. A digital sensor physically outputs on/off or high/low, can only output a certain voltage or no voltage. Digital sensors allow a microcontroller to detect binary state changes. And example of a digital sensor is a push button switch.


3. A pulldown resistor "pulls down" remaining voltage, removing any chance for electrical interference when sensing using a microcontroller. It ensures that there is no floating voltage in any given component that could skew readings and cause undesirable results. It enforces a known state for sensor signals.


void setup() {
  // set the inputs and outputs
  pinMode(2, INPUT); // set pushbutton pin to be an input
  pinMode(3, OUTPUT); //set led 1 to be an output

void loop() {
  // read the pushbutton input:
  if (digitalRead(2) == HIGH) {
    //if push button is closed: LED is ON
    digitalWrite(3, HIGH);
  } else {
    // if push button is open: LED is OFF
    digitalWrite(3, LOW);



byte flag = 0;

void setup() {
  // initialize serial communications at 9600 bps:
  // set inputs and outpus
  pinMode (2, INPUT);

void loop() {
  // when button is pushed, print PUSHED

  if (digitalRead(2) == HIGH && flag == 0) {
    Serial.println ("PUSHED");
    flag = 1;
  //When button is released, print RELEASED

  if (digitalRead(2) == LOW && flag == 1) {
    Serial.println ("RELEASED");
    flag = 0;

Lab 1: Tone

This lab showed us how to hook up the speaker to modulate the volume and/or frequency using an analog sensor.

Tone output using pressure sensor

Here's the code:

void setup() {

void loop() {
int sensorReading = analogRead(A0); //read analog input
float frequency = map(sensorReading, 0, 1000, 500, 1500);
tone(8, frequency, 10);

Tone output with frequency modulation using a potentiometer

Here's the Code:

void setup() {

void loop() {
int sensor = analogRead(A0);
int frequency = map(sensor, 0, 1023, 1000, 5000);
tone(9, frequency);

Lastly, here's me playing with a servo motor, whose angle is mapped to the pressure applied to the sensor.

Here's the code:

#include <Servo.h>
Servo servoMotor;

void setup() {
  Serial.begin(9600);       // initialize serial communications
void loop()
  int analogValue = analogRead(A0); // read the analog input
  Serial.println(analogValue);      // print it
  int servoAngle = map(analogValue, 50,1023,0,179);
  if(millis() % 20<2) {


The labs went pretty well, but I do have a couple of questions after playing with the pressure sensor.

  1. I couldn't find the "pitches.h" file to include for the melody lab on the website, I'm not sure if there's another location of the file so I wasn't able to complete that part of the lab - but I read through and I understand the gist of it.

  2. I noticed that the pressure sensor has some noisy levels when nothing is touching it. I'm guessing it's just really sensitive and maybe registering air pressure, but the readings range from 0-15 with no human pressure applied. I tried using the map function to filter out those lower values, but I'm not sure if it worked.

  3. Follow-up to the last question. I noticed when using the pressure sensor on my servo motor that the servo motor was making a buzzing noise when the sensor wasn't being touched. I again tried to filter out the lower values using the map function but it didn't work and buzzing persisted off and on. I wonder if there's something wrong with my circuit?


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