Week 7

Ideation

Tell us about your assignment's idea for this week. Why do you care about this idea? What inspired you? (Please include images or links to sources of inspiration)

Anti-theft app

For this week’s assignment I’m making a compact anti-theft gadget that lives in your backpack. It’s inspired by a phone app I once used that sounds an alarm when my phone is removed from my pocket. I’m recreating that behavior as a physical device.

I found a similar project on Instructables using Arduino that was also a source of inspiration: https://www.instructables.com/Arduino-Anti-Theft-Device/

Tool Chain

Which software/machines/materials did you use in the assignment? Why?

To simulate the circuit:

To operate the circuit:

Arduino IDE

Electronic Materials:

Arduino Uno & USB cable

Jumper wires

Breadboard

Crocodile wires

220 ohm resistor

Piezo buzzer

ON/OFF switch

LEDs

Ultrasonic sensor

Materials for the enclosure:

Cardboard

Cutter

Masking tape

Design/Preparation Process

Explain the design and/or preparation process of your assignment. How did you use the tool or software to design and/or prepare your assignment before fabrication/implementation?

Planning

Materials needed to build the circuit

Circuit design on Tinkercad:

Connected 5v and GND to rails on breadboard
Connected 2x LEDs to 2x 220 ohm resistors linked to the negative rail

red LED anode: pin 13
green LED anode: pin 12

Connected piezo buzzer to negative rail and pin 10
Connected ultrasonic sensor

VCC to positive rail
GND to negative rail
ECHO to pin 2
TRIGig to pin 3

Connected switch to pin 5 and negative rail

Input components:

ON/OFF switch
Ultrasonic sensor

Action components:

Buzzer
Green LED
Red LED

Wiring on Tinkercad

Development/Implementation Process

Explain the development/implementation process of your assignment. How did you use the machine/tool to manufacture or implement the design of your assignment?

Gathered all materials

Connected 5v and GND to rails on breadboard

Piezo buzzer to negative rail and pin 10

3. connected ultrasonic sensor:

VCC to positive rail
GND to negative rail
ECHO to pin 2
TRIG to pin 3

(this picture was taken before I fixed the TRIG and ECHO to the pins written above)

4. Connected 2x LEDs to 2x 220 ohm resistors linked to the negative rail on breadboard

red LED anode: pin 13
green LED anode: pin 12

5. Connected switch to pin 5 and negative rail using a combination of crocodile wires and jumper wires

Final circuit:

1) Pin declarations

const int trigPin = 5;

const int echoPin = 3;

const int piezo = 10;

const int greenLED = 12;

const int redLED = 8;

const int switchPin = 6;

Defines which Arduino pins connect to which hardware
trigPin and echoPin: ultrasonic sensor
piezo: buzzer/piezo
greenLED / redLED: colour of LEDs
switchPin: switch

2) Variables

float duration, distance;

Variable needed when using an ultrasonic sensor

3) setup()

void setup() {

pinMode(trigPin, OUTPUT);

pinMode(echoPin, INPUT);

pinMode(piezo, OUTPUT);

pinMode(greenLED, OUTPUT);

pinMode(redLED, OUTPUT);

pinMode(switchPin, INPUT_PULLUP);

Serial.begin(9600);

}

Configure pin directions.
INPUT_PULLUP: the switch reads HIGH when open, LOW when closed (pressed)
Serial.begin(9600) opens the serial monitor for debugging

4) loop()

Send ultrasonic pulse (short HIGH on trigPin).
Measure echo time (pulseIn(echoPin, HIGH)).
Convert to distance = (duration * 0.0343) / 2.
Print distance to serial
Read switch (LOW = pressed).
If switch is pressed and object is closer than threshold:
- Red LED + buzzer ON, Green LED OFF.
Else:
- Green LED ON, Red LED + buzzer OFF.

Final working code:

IMG_5567.MOV

Making the cardboard enclosure:

Removed the LEDs from the breadboard and fixed them to the jumper wires using masking tape

Elongated the wires so they can come outside the bag

Made a cardboard box to fit all the components and left some space in the corners for the wires to come out

Final enclosure with USB wire, LEDs, switch and wire to connect to adaptor outside the enclosure

Final working circuit with enclosure:

IMG_5578.MOV

Enclosure in backpack:

IMG_5577.MOV

Overcoming Challenges

When you got stuck, what/who did you turn to? At what point did you have to pause to research or learn more before moving on? What are some mistakes, pitfalls, or challenges that others can avoid if they were doing this assignment?

When I first wrote the code, it was missing the calculations for the ultrasonic sensor, and the serial monitor gave no feedback. I revisited the self-practice videos and compared them with the internet code I had used as a base, which lacked the correct calculations. I then found another code with the right calculations and added the rest of the logic, since I was struggling to start from scratch.

At one point, I also realized I hadn’t added code to make the ultrasonic sensor’s trigger pin LOW at the start of the void loop. I learned this while researching how to use the sensor when it wasn’t working.

Despite this, the ultrasonic sensor kept reading around 1000. After changing pins and troubleshooting with instructors, we concluded the sensor was faulty. I replaced it, and it worked.

Another issue I faced was that my switch was not working. An instructor helped me to test the switch using the serial monitor. When the switch was on, the serial monitor was supposed to send "hello". We came to the conclusion that the switch was not working as the serial monitor was constantly reading "hello". I used a momentary push button and it worked.

Finally, my initial circuit lacked an external power source, which explains why multiple loads were not working at the same time. Since the ultrasonic sensor requires a lot of power, there wasn’t enough for the LEDs, buzzer, and switch. My instructor suggested connecting an external power source to the breadboard with a shared ground (brown wire) and wiring the sensor’s positive and negative to that source.

Connecting an external power source

First draft of code

Assignment Design Files

Code

Circuit on Tinkercad

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