Sunset Receipt Printer

Project Overview

In this video, I'm showing the system in demo mode that condenses what is supposed to happen in a day to 30 seconds: the LED strip displays a range of colors corresponding to the time of day. I manually pressed the "print" button on the back panel of the box to print an additional sunset receipt. At the end, I ripped the receipt from the box opening to keep. 

The receipt is printed from an opening on the front panel of the box that is cut to the width of the receipt paper.

Process

Discussion

From ideation to in-class crits to implementation, I learned a lot throughout each step of the process. I found the in-class crits surprisingly helpful because they helped me consider important aspects that I would've otherwise forgotten. For example, Zar mentioned in the 10/29/25 peer feedback session, "You could maybe add a manual override print button that will print out the sunset time even if it’s more than an hour before, so that if you happen to not be near the printer an hour before, you can still check." This comment was extremely helpful because I did not consider the big picture of my day-to-day life while interacting with the system, of when I might have times that I would want a sunset receipt, either to show another friend or have a physical reminder to take with me if I will not be sitting at the studio desk. Another comment that I vividly remembered from the feedback session was when Helios proposed the idea of incorporating "a display to make it a real-time clock while it wasn’t printing." I did not end up taking his suggestion because I believe that adding this feature would take away the tangible and whimsical aspect of the sunset receipt printer, which gives a surprising physical souvenir every day to remind you to be present in the world around us. I feel that incorporating a digital display would not match my original idea and would make it feel more like an existing phone/ digital clock. 

Reflecting on the project, I'm generally happy with how it turned out, especially because it functions without any bugs. It satisfied my primary goal of creating a tangible interaction that encourages me to step outside and connect to the natural cycle of the sun. However, I do feel that I can work more on the fabrication of the container to make it seem more refined. At this stage, I felt that the figure joints felt too raw and not as complete as I would like them to look. If I had more time, I would increase the distance between the LED strips and the acrylic to better diffuse the lights and use a frosted acrylic for a smoother look. If possible, I would also like to experiment with woodworking instead of laser cutting to further customize the look of the box.

Throughout this process, I learned that my workflow can sometimes constrain my creative ideas and often compromises the interaction and fabrication design for technical feasibility. For example, while making a physical container for the electronics, I realized that it takes much longer than I anticipated, especially building the box in fusion, and making consideration of the spacing for each individual component. It is also much more time-consuming because there are physical and timing constraints on when I can use the laser cutter, and going back and forth to reiterate the box dimensions and form. If I could advise my past self, I would consider all aspects of building the project from software to hardware to fabrication equally, and scope it to the limitations while maximizing the creative output. 

For next steps, I plan on iterating on this project by adding more features to the box to make it feel more interactive, rather than a passive printing machine.  I would also hope to work more on creating a better container for the system to make it feel like a polished table add-on that would add to the aesthetic appearance of my studio table.

Technical information

/*

Project Title: Sunset Receipt + LED Time Lamp

 Author: Yutong Zhen

    This project uses a DS3231 real-time clock, a thermal printer, 

    and a NeoPixel LED strip to create a physical "sunset reminder" device.

    Each day, one hour before local sunset in Pittsburgh, PA, the system 

    prints a receipt containing the sunset time. A manual print button and an LED demo mode button are also included. 

 The LED strip visualizes the time of day through a smooth color 

    transition:

      - 6AM → 12PM: Blue → Yellow

      - 12PM → 6PM: Yellow → Red

      - 6PM → 9PM: Orange → Purple

      - Night: Off

    A demo mode switch allows the full 6AM–9PM cycle to play back 

    over 1 minute for quick presentation.

pin mapping:

Arduino pin | role | description

___________________________________________________________________

2 input attached button for printing

3 input attached to button for LED Demo mode 

4 output attached to LED strip

5 output attached to RX of thermal printer

6 output attached to TX of thermal printer

SDA, SCL input attached to RTC: I2C 

Code written by ChatGPT on 11/2/2025

Edited by Yutong Zhen, yzhen2@andrew.cmu.edu

*/

#include <Wire.h>

#include "RTClib.h"

#include "Adafruit_Thermal.h"

#include <SoftwareSerial.h>

#include <Adafruit_NeoPixel.h>

#include <math.h>

// -------------------- Hardware Setup --------------------

RTC_DS3231 rtc;

SoftwareSerial mySerial(5, 6);   // RX, TX for Thermal Printer

Adafruit_Thermal printer(&mySerial);

#define BUTTON_PIN 2              // Momentary button for printing

#define DEMO_SWITCH_PIN 3         // Latching switch for demo mode

#define LED_PIN 4

#define NUM_LEDS 20

Adafruit_NeoPixel strip(NUM_LEDS, LED_PIN, NEO_GRB + NEO_KHZ800);

// -------------------- Pittsburgh Location --------------------

#define LATITUDE 40.44

#define LONGITUDE -79.99

#define TIMEZONE -5.0   // EDT (-5 for EST)

// -------------------- Global Variables --------------------

bool printedToday = false;

int lastDay = -1;

bool lastButtonState = HIGH;

bool demoMode = false;

// --- Demo mode patch variables ---

bool lastDemoMode = false;

unsigned long demoStartMillis = 0;

// -------------------- Date Helpers --------------------

int dayOfYear(int year, int month, int day) {

 static const int monthDays[12] =

   {31,28,31,30,31,30,31,31,30,31,30,31};

 int n = day;

 for (int i = 0; i < month - 1; i++) n += monthDays[i];

 if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)

   if (month > 2) n++;

 return n;

}

// -------------------- Sunset Calculation --------------------

double computeSunsetTime(int n, double lat, double lon, double tz) {

 double rad = M_PI / 180.0;

 double decl = 23.45 * sin(rad * ((360.0/365.0)*(284+n)));

 double B = (360.0/365.0) * (n - 81);

 double EoT = 9.87 * sin(2*rad*B) - 7.53 * cos(rad*B) - 1.5 * sin(rad*B);

 double H = acos(-tan(rad*lat) * tan(rad*decl)) / rad;

 double sunsetSolar = 12.0 + (H / 15.0);

 double lonHours = lon / 15.0;

 return sunsetSolar - (EoT/60.0) - lonHours + tz;

}

// -------------------- Receipt Printing --------------------

void printSunsetReceipt(DateTime now, int sunsetH, int sunsetM) {

 printer.wake();

 printer.justify('C');

 printer.setSize('L');

 printer.println(F("SUNSET"));

 printer.setSize('L');

 printer.print(sunsetH);

 printer.print(":");

 if (sunsetM < 10) printer.print("0");

 printer.print(sunsetM);

 printer.println(" PM");

 printer.println();

 printer.setSize('S');

 printer.println(F("Pittsburgh, PA"));

 printer.print(F("Date: "));

 printer.print(now.month());

 printer.print("/");

 printer.print(now.day());

 printer.print("/");

 printer.println(now.year());

 printer.println();

 printer.println(F("Go take a walk!"));

 printer.println();

 printer.println();

 printer.println();

 printer.println();

  printer.feed(3);

 printer.sleep();

 Serial.println("✅ Sunset receipt printed.");

 Serial.print(now.month());

 Serial.print("/");

 Serial.print(now.day());

 Serial.print("/");

 Serial.print(now.year());

 Serial.print(" ");

 Serial.print(now.hour());

 Serial.print(":");

 if (now.minute() < 10) Serial.print("0");

 Serial.print(now.minute());

 Serial.print(":");

 if (now.second() < 10) Serial.print("0");

 Serial.println(now.second());

}

// -------------------- LED Color Function --------------------

uint32_t timeToColorMinutes(int t) {

 int r, g, b;

 // 6AM → 12PM: Blue → Yellow (360–720)

 if (t >= 360 && t < 720) {

   float p = float(t - 360) / 360.0;

   r = int(255 * p);

   g = int(255 * p);

   b = int(255 * (1 - p));

 // 12PM → 6PM: Yellow → red (720–1080)

 } else if (t >= 720 && t < 1080) {

   float p = float(t - 720) / 360.0;

   r = 255;

   g = 255 - int(p * (255));  // 255 → 120

   b = 0;

 // 6PM → 9PM: Orange → Purple (1080–1260)

 } else if (t >= 1080 && t < 1260) {

   float p = float(t - 1080) / 180.0;

   r = 255 - int(p * (255 - 100));  // 255 → 100

   g = 120 - int(p * 120);          // 120 → 0

   b = int(p * 255);                // 0 → 255

 // Night: LEDs off

 } else {

   r = g = b = 0;

 }

 return strip.Color(r, g, b);

}

// -------------------- Setup --------------------

void setup() {

 Wire.begin();

 rtc.begin();

 mySerial.begin(19200);

 delay(500);

 printer.begin();

 printer.setDefault();

 Serial.begin(9600);

 pinMode(BUTTON_PIN, INPUT_PULLUP);

 pinMode(DEMO_SWITCH_PIN, INPUT_PULLUP);

 strip.begin();

 strip.show();

 Serial.println("System initialized with Demo Mode support.");

}

// -------------------- Main Loop --------------------

void loop() {

 DateTime now = rtc.now();

 // -------- Read demo switch --------

 demoMode = (digitalRead(DEMO_SWITCH_PIN) == HIGH);

 // Detect transition: OFF → ON, reset demo timer

 if (demoMode && !lastDemoMode) {

   demoStartMillis = millis();

 }

 // -------- Compute minutes (demo or normal) --------

 int minutesNow;

 if (!demoMode) {

   // Normal mode = real time

   minutesNow = now.hour() * 60 + now.minute();

 } else {

   // Demo mode = compress 6AM–9PM into 1 minute, starting fresh every time

   unsigned long ms = (millis() - demoStartMillis) % 60000; // 0–59999

   float p = ms / 30000.0;                                  // 0–1 progress

   minutesNow = 360 + int(p * (1260 - 360));                // map 6AM–9PM

 }

 // Track last state

 lastDemoMode = demoMode;

 // -------- Sunset Calculations --------

 int n = dayOfYear(now.year(), now.month(), now.day());

 double sunsetHour = computeSunsetTime(n, LATITUDE, LONGITUDE, TIMEZONE);

 int sunsetH = int(sunsetHour);

 int sunsetM = int((sunsetHour - sunsetH) * 60);

 double printHour = sunsetHour - 1;

 if (printHour < 0) printHour += 24;

 int printH = int(printHour);

 int printM = int((printHour - printH) * 60);

 // -------- Automatic print one hour before sunset --------

 if (!printedToday && now.hour() == printH && now.minute() == printM) {

   printSunsetReceipt(now, sunsetH, sunsetM);

   printedToday = true;

   lastDay = now.day();

 }

 // -------- Manual print --------

 bool buttonState = digitalRead(BUTTON_PIN);

 if (buttonState == LOW && lastButtonState == HIGH) {

   delay(50);

   if (digitalRead(BUTTON_PIN) == LOW) {

     printSunsetReceipt(now, sunsetH, sunsetM);

   }

 }

 lastButtonState = buttonState;

 // Reset for new day

 if (now.day() != lastDay) printedToday = false;

 // -------- Update LEDs --------

 uint32_t color = timeToColorMinutes(minutesNow);

 for (int i = 0; i < NUM_LEDS; i++) {

   strip.setPixelColor(i, color);

 }

 strip.show();

 delay(1000);

}