Standalone-electricity-price-ticker/HARDWARE_WIRING_DIAGRAM.md

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.

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1) Wiring overview (diagram)

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;

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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

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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.

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4) Included peripherals checklist

• Seeed XIAO ESP32‑C3
• 20x4 I²C LCD (PCF8574 backpack)
• Pushbutton (or touch alternative using same GPIO)
• Presence sensor RCWL‑0516 (optional)
• 10 kΩ pull‑down resistor for presence sensor (required when used)
• White LED output / LED strip driver (optional)