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HARDWARE_WIRING_DIAGRAM.md

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+# Hardware Wiring Diagram (Seeed XIAO ESP32‑C3 Electricity Price Ticker)
+
+This document depicts the wiring for the **Electricity Price Ticker** project based on the connection instructions in `README.md`.
+
+It includes:
+- Required peripherals (LCD + button)
+- Supported optional peripherals (presence sensor + white LED / LED strip driver)
+
+> Notes:
+> - Always connect **all grounds together** (ESP32 GND, LCD GND, sensor GND, LED driver GND, external PSU GND).
+> - Verify your **XIAO ESP32‑C3 SDA/SCL pins** in the Seeed pinout; the sketch uses the board default I²C pins.
+
+---
+
+## 1) Wiring overview (diagram)
+
+```mermaid
+flowchart TB
+  MCU[Seeed XIAO ESP32‑C3]:::mcu
+
+  LCD[20x4 I²C LCD (2004)\nPCF8574 backpack\nAddr: 0x27]:::lcd
+  BTN[Momentary pushbutton\n(active LOW via INPUT_PULLUP)]:::btn
+  PRES[RCWL‑0516 presence sensor (optional)]:::pres
+  LED[White LED / LED strip control (optional)]:::led
+  RPD[10 kΩ pull‑down resistor\n(required for presence sensor)]:::res
+  MOSFET[MOSFET / transistor driver\n(recommended for LED strips)]:::drv
+
+  PSU5V[5V supply\n(USB‑C or regulated 5V)]:::pwr
+  PSU3V3[3.3V rail\n(from XIAO)]:::pwr
+  GND[(Common GND)]:::gnd
+
+  %% Power
+  PSU5V -->|5V| MCU
+  PSU5V -->|5V (or 3V3 if LCD supports it)| LCD
+  MCU -->|3V3| PSU3V3
+  PSU3V3 -->|3.3V| PRES
+
+  %% Grounds
+  MCU --- GND
+  LCD --- GND
+  PRES --- GND
+  LED --- GND
+  MOSFET --- GND
+  PSU5V --- GND
+
+  %% I2C
+  MCU -->|SDA| LCD
+  MCU -->|SCL| LCD
+
+  %% Button
+  MCU -->|GPIO 4 (buttonPin)| BTN
+  BTN -->|to GND| GND
+
+  %% Presence sensor
+  MCU -->|GPIO 9 (presencePin)| PRES
+  RPD -->|10 kΩ| GND
+  MCU -->|GPIO 9 node| RPD
+
+  %% White LED / strip driver
+  MCU -->|GPIO 5 (whiteLedPin)| LED
+  MCU -->|GPIO 5 (better)| MOSFET
+  MOSFET -->|drives| LED
+
+classDef mcu fill:#e8f0ff,stroke:#2b5fd9,stroke-width:1px,color:#000;
+classDef lcd fill:#fff4e5,stroke:#cc7a00,stroke-width:1px,color:#000;
+classDef btn fill:#eaffea,stroke:#2d8a2d,stroke-width:1px,color:#000;
+classDef pres fill:#f3e8ff,stroke:#7b2cbf,stroke-width:1px,color:#000;
+classDef led fill:#ffe8ef,stroke:#c9184a,stroke-width:1px,color:#000;
+classDef res fill:#f5f5f5,stroke:#444,stroke-width:1px,color:#000;
+classDef drv fill:#f5f5f5,stroke:#444,stroke-width:1px,color:#000;
+classDef pwr fill:#fff,stroke:#444,stroke-width:1px,color:#000;
+classDef gnd fill:#fff,stroke:#000,stroke-width:1.5px,color:#000;
+```
+
+---
+
+## 2) Pin mapping (as used by the sketch)
+
+| Peripheral | Signal | XIAO ESP32‑C3 pin | Notes |
+|---|---:|---:|---|
+| LCD (I²C, PCF8574) | SDA | **Board I²C SDA** | Check Seeed pinout for your board variant |
+| LCD (I²C, PCF8574) | SCL | **Board I²C SCL** | Check Seeed pinout for your board variant |
+| LCD (I²C, PCF8574) | VCC | **5V** (or 3V3) | Many LCD backpacks expect 5V; use 3V3 only if your module supports it |
+| LCD (I²C, PCF8574) | GND | GND | Common ground |
+| Button | input | **GPIO 4** (`buttonPin`) | Sketch uses `INPUT_PULLUP`; wiring is button → GPIO4 and button → GND |
+| Presence sensor (RCWL‑0516, optional) | OUT | **GPIO 9** (`presencePin`) | Requires pull‑down resistor |
+| Presence sensor (RCWL‑0516, optional) | VCC | **3.3V** | Recommended 3.3V |
+| Presence sensor (RCWL‑0516, optional) | GND | GND | Common ground |
+| Pull‑down resistor (required if presence sensor used) | 10 kΩ | **GPIO 9 → GND** | Stabilizes the OUT line |
+| White LED (optional) | control | **GPIO 5** (`whiteLedPin`) | Use series resistor for a single LED |
+| LED strip driver (recommended for strips) | gate/base | **GPIO 5** | Use a MOSFET/transistor + external supply; do not power strips from GPIO |
+
+---
+
+## 3) Practical wiring notes
+
+### LCD (I²C)
+- The sketch instantiates: `LiquidCrystal_I2C lcd(0x27, 20, 4);`
+- If your LCD uses a different I²C address, you must change `0x27`.
+
+### Button (default)
+- Recommended wiring:
+  - One leg of the button → **GPIO 4**
+  - Other leg → **GND**
+- The code reads it as active-low using:
+  - `pinMode(buttonPin, INPUT_PULLUP);`
+  - `int reading = !digitalRead(buttonPin);`
+
+### Presence sensor (RCWL‑0516, optional)
+- Wiring:
+  - `VCC` → **3.3V**
+  - `GND` → **GND**
+  - `OUT` → **GPIO 9**
+  - **10 kΩ pull‑down** between **GPIO 9** and **GND** (required)
+
+### White LED / LED strip output (optional)
+- Single LED wiring:
+  - **GPIO 5 → series resistor (220–470 Ω) → LED anode**
+  - LED cathode → **GND**
+- LED strip / higher current:
+  - Use a logic-level MOSFET (or suitable transistor) and an external PSU.
+  - Ensure **common ground** between PSU and ESP32.
+
+---
+
+## 4) Included peripherals checklist
+
+- [x] Seeed XIAO ESP32‑C3
+- [x] 20x4 I²C LCD (PCF8574 backpack)
+- [x] Pushbutton (or touch alternative using same GPIO)
+- [x] Presence sensor RCWL‑0516 (optional)
+- [x] 10 kΩ pull‑down resistor for presence sensor (required when used)
+- [x] White LED output / LED strip driver (optional)