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--- pm:prj2026:theodor_ioan.buliga:adrian.vancea [2026/05/27 07:46]
adrian.vancea
+++ pm:prj2026:theodor_ioan.buliga:adrian.vancea [2026/05/27 08:11] (current)
adrian.vancea [Results]
@@ Line 1: / Line 1: @@
-====== Portable MP3 Player ======
+{{:pm:prj2026:theodor_ioan.buliga:portable_mp3_player.zip|}}====== Portable MP3 Player ======
 ===== Introduction =====
@@ Line 283: / Line 283: @@
 ===== Results =====
+The final product is a functional, standalone portable MP3 player built around
+the Arduino Nano and DFPlayer Mini, with a custom OLED user interface written
+entirely without external libraries.
+{{:pm:prj2026:theodor_ioan.buliga:whatsapp_image_2026-05-27_at_08.06.10.jpeg?500|}}
+{{:pm:prj2026:theodor_ioan.buliga:whatsapp_image_2026-05-27_at_08.08.02.jpeg?500|}}
+{{:pm:prj2026:theodor_ioan.buliga:whatsapp_image_2026-05-27_at_08.05.58.jpeg?500|}}
+**Functional features achieved:**
+  * Playback of MP3 files from a microSD card with Play / Pause / Next / Previous control
+  * 3-mode user interface (Track Mode, Volume Mode, Track Select) managed by a state machine
+  * OLED display showing a 16px scaled track number and play/pause icon, a spectrum bar animation, elapsed time, and a volume indicator bar
+  * Volume control (0–10 steps) via long-press + short-press button interaction
+  * Track select menu listing all available tracks (auto-detected from SD card at startup)
+  * Spectrum animation that instantly flattens to a straight line on pause
+  * Portable power supply: 3.7V Li-Po battery with TP4056 charging and protection circuit
+  * Stereo audio output via 3.5mm jack
+**Performance measurements:**
+  * Main loop iteration: ~110ms (10ms active delay + ~100ms I2C framebuffer flush)
+  * Firmware RAM usage: 54.8% (1123 / 2048 bytes) — stable, no stack overflow observed
+  * Firmware Flash usage: 11.4% (3502 / 30720 bytes) — significant headroom remaining
+  * Button response latency: max 110ms (one loop iteration) — imperceptible in practice
+  * Volume range: 0–30 on DFPlayer (mapped from 0–10 user-facing steps)
+**Hypothesis validation:** \\
+The initial hypothesis was confirmed. Offloading audio decoding to the DFPlayer Mini
+allowed the ATmega328P to dedicate its full cycle budget to UI rendering and button
+polling, resulting in a smooth 9 FPS display refresh with no audio glitches.
 ===== Conclusions =====
-===== Download =====
+The project successfully demonstrates a balanced embedded system where dedicated
+hardware (DFPlayer) handles the computationally expensive task (MP3 decoding) while
+the microcontroller focuses on user interaction and visual feedback.
+**What worked well:**
+  * The bare-metal approach (no libraries) gave full control over timing and memory,
+    which was essential given the 2KB RAM constraint of the ATmega328P.
+  * The software UART bit-bang implementation proved reliable for DFPlayer communication
+    and also enabled reading the track count response at startup.
+  * The framebuffer rendering approach (draw everything into RAM, flush once) eliminated
+    partial-update artifacts on the OLED.
+  * The hold-counter button logic (short press vs. long press on the same button) reduced
+    the required number of physical buttons from 5 to 3 without sacrificing usability.
+**Challenges encountered:**
+  * The ''oled_char'' (uses ''='') vs. ''draw_pixel'' (uses ''|='') page conflict required
+    careful layout planning to avoid text erasing pixel graphics in the same page byte.
+  * DFPlayer communication is sensitive to timing — the soft UART bit period (104µs)
+    had to be exact, and any I2C activity during transmission caused corruption.
+  * Power stability: the Li-Po voltage drop under load initially caused resets;
+    resolved by adding a decoupling capacitor near the Arduino VIN pin.
+**Future improvements:**
+  * Replace the simulated spectrum with a real VU meter using the ADC and a signal
+    tap from the audio line.
+  * Add a progress bar using DFPlayer command 0x28 (query current playback position).
+  * Design a custom PCB to reduce size and improve reliability over the prototype board.
 ===== Journal =====
-  * **May 3**: Created the Wiki documentation page and the Block Diagram.
+  * **May 3**: Created the Wiki documentation page and the Block Diagram. Defined project scope and selected components.
-  * **May 10**: Hardware milestone reached: Developed the full system schematic including power management (TP4056) and audio routing. Verified the I2C and UART pin mapping. Added a visual demonstration of the functional prototype showing stable communication between all modules.
+  * **May 10**: Hardware milestone: developed the full system schematic in KiCad including power management (TP4056) and audio routing. Verified I2C and UART pin mapping on breadboard. Confirmed stable communication between Arduino, OLED, and DFPlayer.
+  * **May 15**: Implemented bare-metal I2C driver (TWI registers) and basic OLED framebuffer rendering. First text displayed on screen.
+  * **May 18**: Implemented software UART TX for DFPlayer control. First successful track playback triggered from firmware. Volume and play/pause commands verified.
+  * **May 20**: Added software UART RX and ''dfp_query_tracks()'' to auto-detect SD card track count at startup. Verified fallback behavior when DFPlayer does not respond.
+  * **May 22**: Implemented spectrum bar animation with smooth attack/decay algorithm. Added instant flatten-to-line behavior on pause.
+  * **May 24**: Designed and implemented the 3-mode state machine (Track / Volume / Track Select). Rewrote button logic to support short press vs. long press on the same button using hold counters.
+  * **May 26**: Added ''draw_big_char()'' function for 2× scaled 16px characters. Redesigned the OLED layout: big icon + track number in top 16px, spectrum in the middle, time and volume bar at the bottom.
+  * **May 27**: Final firmware build verified: RAM 54.8%, Flash 11.4%, no compilation errors. Assembled final prototype on PCB board. Completed Wiki documentation.
 ===== Bibliography/Resources =====
@@ Line 299: / Line 362: @@
   * SSD1306 OLED Tutorials
   * Project Schematic: {{:pm:prj2026:theodor_ioan.buliga:proiect_pm_v2.pdf|}}
+  * Project Code : {{:pm:prj2026:theodor_ioan.buliga:portable_mp3_player.zip|}}
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