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--- pm:prj2026:theodor_ioan.buliga:catalin.manole1211 [2026/05/04 19:39]
catalin.manole1211 [Bibliografie/Resurse]
+++ pm:prj2026:theodor_ioan.buliga:catalin.manole1211 [2026/05/27 04:29] (current)
catalin.manole1211
@@ Line 1: / Line 1: @@
-====== Walkie Talkie With Print Verification ======
+====== Secure Communication Terminal ======
 ===== Introduction =====
-The **Walkie Talkie With Print Verification** project is a fully digital, hardware-secured wireless communication terminal. Unlike a classic radio station, the device allows real-time voice capture, P2P transmission, and playback only if the user passes a **biometric authentication** filter. The system integrates a permission-based access hierarchy (Admin vs. User) and is controlled by an ESP32 microcontroller.
+The **Secure Communication Terminal** project is a digital, secured wireless communication device. Unlike a classic radio station, the device allows real-time voice capture, P2P transmission, and playback only if the user passes a **biometric authentication** filter. The system integrates a permission-based access hierarchy (Admin vs. User) and is controlled by an ESP32 microcontroller.
 **What is its purpose:**
@@ Line 10: / Line 10: @@
 **What was the starting idea:**
 The idea stemmed from the main vulnerability of conventional analog radio stations: lack of security. Anyone owning a station on the same frequency can listen or transmit. I thought about how I could implement a fundamental principle of cybersecurity (*Access Control* based on "Something you are") directly into the physical environment, transforming a simple communication station into a strictly restricted data terminal.
 ===== General Design =====
-To illustrate the architecture of the **Walkie-Talkie with Print Verification**, I have created a block diagram highlighting the hardware components and the data flow (communication protocols) between the peripherals and the central processing unit.
+To illustrate the architecture of the **Secure Communication Terminal**, I have created a block diagram highlighting the hardware components and the data flow (communication protocols) between the peripherals and the central processing unit.
 {{:pm:prj2026:theodor_ioan.buliga:diagramdrawn.jpg?700|}}
 ==== User Roles & Access Control ====
-The Walkie-Talkie supports two types of users: **Admin** and **General User**.
+The terminal supports two types of users: **Admin** and **General User**.
   * The Admin fingerprint is permanently stored and cannot be modified or overwritten.
   * Only the Admin has the authority to enroll or remove a General User's fingerprint.
@@ Line 30: / Line 29: @@
 If the device is unlocked (a user is logged in), the incoming audio is actively played through the speaker. Once authenticated, the user can receive and transmit freely for a **2-minute session** before the system automatically times out, locks itself, and requires re-authentication.
-The reset button must be held for 5 seconds to perform a full reset of the system. The user data is lost upon resetting.
+The reset button must be held for 5 seconds to perform a full reset of the system.
 ===== Hardware Design =====
 | Component | Quantity | Description | Interface |
-| **ESP32 DevKit V1** | 2 | Main Microcontroller (Dual-core, Wi-Fi/BT) | - |
+| --- | --- | --- | --- |
-| **AS608 Sensor** | 2 | Optical/Capacitive Biometric Sensor | UART |
+| **ESP32 DevKit V1** | 2 | Main Microcontroller (WROOM-32) | - |
-| **INMP441 Mic** | 2 | Digital I2S Microphone | I2S |
+| **AS608 Sensor** | 2 | Optical Biometric Fingerprint Sensor | UART |
-| **MAX98357A Amp** | 2 | I2S DAC + Class D Amplifier | I2S |
+| **INMP441 Mic** | 2 | Digital Omnidirectional Microphone | I2S0 |
+| **MAX98357A Amp** | 2 | I2S DAC + Class D Audio Amplifier | I2S1 |
 | **SSD1306 OLED** | 2 | 0.96" Monochrome Display (128x64) | I2C |
-| **Mini Speaker** | 2 | 8 Ohm, 3W | Analog |
+| **Mini Speaker** | 2 | 20x30mm Rectangular Speaker (1W) | Analog |
 | **Tactile Buttons** | 6 | PTT, Admin Mode, Reset | GPIO |
+| **Battery Holder** | 2 | 4 x AA Slots Enclosure | Power |
+| **NiMH AA Batteries** | 8 | 1.2V Rechargeable Cells (4.8V pack per terminal) | Power |
+| **Custom Enclosure** | 2 | 3D Printed Case & Breadboard Assembly | Mechanical |
+| **DuPont Wires** | Set | Male-to-Male / Male-to-Female Jumpers | Wiring |
-**Description:**
+**System Architecture & Power Management:**
-The hardware architecture centers on the ESP32, managing biometric security via UART and real-time audio through the I2S protocol. Digital peripherals (INMP441 and MAX98357A) ensure high-fidelity communication, while the OLED display and tactile buttons provide a responsive user interface for secure, peer-to-peer wireless transmission.
+The hardware architecture centers on the ESP32, managing biometric security via UART and real-time audio through concurrent I2S buses. A critical design decision was made to ensure portability and prevent brownout resets during high-current audio playback.
+The system is powered by a 4-cell AA battery holder utilizing NiMH rechargeable batteries (providing a stable ~4.8V). This power source is connected directly to the ESP32's ''VIN'' pin and the MAX98357A amplifier. This maximizes the audio output volume (staying safely below the amplifier's 5.5V absolute maximum rating) while allowing the ESP32's internal 3.3V regulator to safely power the logic-level peripherals (OLED, Mic, Fingerprint Sensor) without being overloaded by audio transients.
+**Detailed Pin Mapping & Motivation:**
+^ Component ^ Peripheral Pin ^ ESP32 Pin ^ Signal Type ^ Design Motivation ^
+| **Power Supply** | Plus (+) Bat. | VIN | Power (4.8V) | System power. Feeds Amp directly and ESP32 regulator. |
+| ::: | Minus (-) Bat. | GND | Ground | Common reference ground. |
+| **Fingerprint (AS608)** | Pin 3 (Green) | 3V3 | Power (3.3V) | Safe operating voltage for the sensor. |
+| ::: | Pin 4 (Yellow) | D16 (RX2) | UART TX | Dedicated hardware UART2 for reliable biometric data. |
+| ::: | Pin 5 (Black) | D17 (TX2) | UART RX | Dedicated hardware UART2. |
+| **Microphone (INMP441)**| VDD | 3V3 | Power (3.3V) | Native digital power. |
+| ::: | L/R | GND | Config | Tied to GND to configure transmission on the Left Channel (Mono). |
+| ::: | WS | D33 | I2S Clock | Allocated to standard output-capable pins for I2S0 Master mode. |
+| ::: | SCK | D18 | I2S BClock | ::: |
+| ::: | SD | D32 | I2S Data | ::: |
+| **Amplifier (MAX98357A)**| VIN | VIN | Power (4.8V) | Powered directly from batteries to prevent ESP32 brownouts. |
+| ::: | LRC / WS | D26 | I2S Clock | Allocated to the secondary I2S1 bus for independent audio output streaming. |
+| ::: | BCLK | D27 | I2S BClock | ::: |
+| ::: | DIN | D14 | I2S Data | ::: |
+| **Speaker** | Positive (+) | Amp OUT+ | Analog | Driven directly by the Class D Amplifier for high-efficiency output. |
+| ::: | Negative (-) | Amp OUT- | Analog | ::: |
+| **OLED (SSD1306)** | VCC | 3V3 | Power (3.3V) | Standard logic power. |
+| ::: | SDA | D21 | I2C Data | Native hardware I2C pins for maximum compatibility with the Wire library. |
+| ::: | SCL | D22 | I2C Clock | ::: |
 ===== Software Design =====
-TBD
+The project's software is built around a robust **Finite State Machine (FSM)** architecture, utilizing **FreeRTOS** capabilities for multitasking and asynchronous interrupt processing. This allows the separation of time-critical tasks (audio streaming) from low-priority tasks (UI updates).
-===== Results =====
+==== Libraries Used ====
-TBD
+* **esp_now.h:** Chosen over classic Wi-Fi or Bluetooth to eliminate router dependency and ensure ultra-low latency, which is essential for voice transmissions (Voice-over-Radio).
-===== Conclusions =====
+* **driver/i2s_std.h (ESP32 IDF):** Used for direct control of the I2S bus. Unlike a standard analog ADC/DAC, I2S allows pure digital reading of the microphone and digital control of the amplifier, ensuring vastly superior audio quality free of circuit interference.
+* **Adafruit_Fingerprint.h:** Chosen for the efficient abstraction of UART communication with the AS608 sensor, greatly simplifying the complex mathematical operations involved in storing and matching biometric matrices.
+* **freertos/queue.h:** Vital for decoupling. It allows the separation of the radio reception process (ISR) from the audio playback process, using a memory queue to guarantee continuous voice playback without blocking.
-===== Download =====
+==== Finite State Machine (FSM) and Logic Flow ====
-<note warning>
+The application backbone runs through transitions between 4 distinct states:
-O arhivă (sau mai multe dacă este cazul) cu fişierele obţinute în urma realizării proiectului: surse, scheme, etc. Un fişier README, un ChangeLog, un script de compilare şi copiere automată pe uC crează întotdeauna o impresie bună ;-).
-Fişierele se încarcă pe wiki folosind facilitatea **Add Images or other files**. Namespace-ul în care se încarcă fişierele este de tipul **:pm:prj20??:c?** sau **:pm:prj20??:c?:nume_student** (dacă este cazul). **Exemplu:** Dumitru Alin, 331CC -> **:pm:prj2009:cc:dumitru_alin**.
+* **STATE_LOCKED / ST_LOCKED:** Default state. The system is completely isolated. The I2S output is muted, and the system polls the AS608 sensor via UART.
-</note>
+* **STATE_UNLOCKED / ST_UNLOCKED:** Reached after a valid fingerprint match. A timer is started (2 minutes).
+* **STATE_WAIT_ADMIN / ST_ADMIN:** An intermediate state triggered when the Admin ID (ID 1) is recognized. Enables 'Enroll' and 'Delete' functions via the Action Button. Features an automatic 5-minute timeout.
+* **STATE_LIVE_STREAM / ST_TRANSMIT:** The "Walkie-Talkie" communication mode. Triggered by the PTT button (GPIO Interrupt), the station switches between Receiver and Transmitter modes (Half-Duplex). Audio is sampled via I2S and sent through ESP-NOW.
-===== Journal =====
+To avoid needing excessive physical buttons, **temporal multiplexing** is used for the Action Button:
+  * **Short Press (< 2s):** If in ''ST_ADMIN'', it triggers the `fingerprintEnroll()` function to add the General User via a 3-step software routine.
+  * **Long Press (> 5s):** If in ''ST_ADMIN'', it triggers `fingerprintDelete(USER_ID)` to wipe the database.
+==== Hardware-Level Encryption (AES-128) ====
+To prevent unauthorized interception of the radio traffic (packet sniffing), the system implements ESP-NOW's native **AES-128** encryption at the MAC layer.
+  * **Symmetric Keying:** A 16-byte secret key (''secretKey'') is hardcoded and shared between the ALPHA and BRAVO terminals. This acts as both the Primary Master Key (PMK) and the Local Master Key (LMK).
+  * **Secure Payload:** By setting ''peerInfo.encrypt = true'' during the peer registration phase, the ESP32's Wi-Fi hardware automatically encrypts the outgoing 240-byte audio payloads and decrypts them upon arrival. This zero-overhead hardware encryption ensures that the P2P voice stream remains strictly confidential.
+==== Communication Protocol & Audio Flow ====
+A major technical challenge was the limitation of the **ESP-NOW** hardware protocol, which strictly supports **250 bytes per payload**.
+System calibration was achieved by reading the microphone stream (which is natively 32-bit) and truncating/packing it into a buffer of exactly **120 samples of 16-bit**. The result is a packet of exactly **240 bytes**, maximizing the available audio bandwidth without hitting the ceiling that would cause packet loss.
+Received packets are captured through an interrupt routine (''OnDataRecv'') triggered asynchronously by the hardware, using the ''xQueueSendFromISR'' command to safely place the data into the playback buffer.
+==== Critical System Optimizations ====
+* **Where:** On the I2C bus (OLED Display).
+* **How:** The ''display.display()'' command was strictly restricted only to the moments when the device changes its state (e.g., transition from TX to RX).
+* **Why:** I2C is a much too slow bus compared to the frequency of the incoming radio packets (dozens per second). Updating the screen for every packet would have led to "CPU starvation", severely fragmenting the audio playback fluency.
+* **Where:** Background Noise Management (I2S Speaker).
+* **How:** In the absence of a valid radio signal in the FreeRTOS queue, the system constantly injects an array of zeros into the amplifier.
+* **Why:** This hardware method completely eliminates electrostatic hiss and white noise while in standby, maintaining absolute "digital silence" until the next transmission.
+===== Results =====
+Demo Link : https://youtube.com/shorts/ny9w-C_flPQ?is=Uj0ZvqpBS-vCuD1a
+===== Download =====
+Project files can be found here:
+https://github.com/Catalin951/Secure-Communication-Terminal/tree/main
-<note tip>
-Puteți avea și o secțiune de jurnal în care să poată urmări asistentul de proiect progresul proiectului.
-</note>
-===== Bibliography/Resources =====
-<html><a class="media mediafile mf_pdf" href="?do=export_pdf">Export to PDF</a></html>