# 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 + optional TTP223 touch button alternative)

> Notes:
> - Always connect **all grounds together** (ESP32 GND, LCD GND, sensor GND, LED GND).
> - Verify your **XIAO ESP32‑C3 SDA/SCL pins** in the Seeed pinout; the sketch uses the board default I²C pins.
> - **Important:** The **10 kΩ pull-down resistor on GPIO 9 is mandatory at all times** (even if the presence sensor is not connected).
> - Button input is on **GPIO 4**. You may use either a **mechanical pushbutton** (default) *or* a **TTP223 touch module** (alternative), but not both in parallel unless you know what you’re doing.

---

## 1) Wiring overview (diagram)

```mermaid
flowchart TB
  MCU["Seeed XIAO ESP32-C3"]:::mcu

  LCD["20x4 I2C LCD 2004<br/>PCF8574 backpack<br/>I2C addr 0x27"]:::lcd

  %% Button input options (GPIO 4)
  GPIO4["GPIO 4 node<br/>(buttonPin input)"]:::io
  BTN["Mechanical pushbutton<br/>default option<br/>active LOW to GND"]:::btn
  TTP["TTP223 capacitive touch<br/>optional alternative<br/>OUT is HIGH when touched"]:::touch

  %% Presence-sensor input stage (GPIO 9) - always present
  GPIO9["GPIO 9 node<br/>(presencePin input)"]:::io
  RPD["10k pull-down resistor<br/>GPIO 9 to GND<br/>MANDATORY"]:::res
  PRES["RCWL-0516 presence sensor<br/>optional"]:::pres

  LED1["White indicator LED<br/>optional"]:::led

  PSU5V["5V supply<br/>USB-C or regulated 5V"]:::pwr
  V33["3.3V rail from XIAO"]:::pwr
  GND["Common GND"]:::gnd

  %% Power
  PSU5V -->|"5V"| MCU
  PSU5V -->|"5V or 3V3 if LCD supports"| LCD
  MCU -->|"3V3"| V33
  V33 -->|"3V3"| PRES
  V33 -->|"3V3"| TTP

  %% Grounds
  MCU --- GND
  LCD --- GND
  BTN --- GND
  TTP --- GND
  GPIO4 --- GND

  GPIO9 --- GND
  RPD --- GND
  PRES --- GND

  LED1 --- GND
  PSU5V --- GND

  %% I2C
  MCU -->|"SDA (board I2C SDA)"| LCD
  MCU -->|"SCL (board I2C SCL)"| LCD

  %% GPIO 4 button input stage (always)
  MCU -->|"GPIO 4 (buttonPin)"| GPIO4
  BTN -->|"button to GND"| GPIO4
  TTP -->|"OUT to GPIO 4 node"| GPIO4

  %% GPIO 9 presence input stage (always)
  MCU -->|"GPIO 9 (presencePin)"| GPIO9
  GPIO9 ---|"10k"| RPD
  RPD -->|"to GND"| GND
  PRES -->|"OUT to GPIO 9 node"| GPIO9

  %% White LED (single LED, directly from GPIO with series resistor)
  MCU -->|"GPIO 5 (whiteLedPin)"| LED1

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