IoT-PostBox v0.x

Legacy technical documentation for IoT-PostBox v0.x series (ESP8266 based). This generation focuses on ultra-low power consumption with hardware wake-up mechanism and basic WiFi connectivity.

Hardware Overview

Top View	3D Rendering	Bottom View

Key Features

Core Platform:

• MCU: ESP8266 (ESP-12F or ESP-07S)
• Connectivity: WiFi 2.4GHz with MQTT support
• Wake-up Method: Hardware reset via CH_PD pin (vs GPIO interrupt in v1.x)
• Power Optimization: Deep sleep with GPIO14 keep-alive mechanism

Power Management:

• Battery Charger: TP4056 with protection circuits
• Single LDO: ME6211 or MCP1700 for power regulation
• Battery Monitoring: ADC-based voltage sensing
• Protection: Overcharge, overdischarge, and overcurrent protection

I/O & Interfaces:

• Switch Sensors: Two hardware wake-up inputs (J1, J2)
• LED Support: WS2812B RGB LED strip (v0.3+)
• Programming: Populated UART and programming pins ready for external TTL-to-USB adapter
• Expansion: Basic GPIO access

Power Management Architecture

Hardware Wake-up System

The v0.x series uses a unique hardware wake-up mechanism optimized for ultra-low power consumption:

Switch Input ──── CH_PD Pin ──── ESP8266 Power Control
     │                                    │
     └──── GPIO14 ──── Keep-Alive Logic ──┘

Wake-up Process:

1. Power Off State: ESP8266 completely powered down (CH_PD low)
2. Event Detection: Switch contact pulls CH_PD high, physically powering on the ESP8266
3. Keep-Alive Activation: Firmware immediately sets GPIO14 high to maintain CH_PD even if switch opens
4. Notification Process: ESP8266 performs WiFi connection and sends MQTT notification
5. Power Down: After configured time/completion, GPIO14 goes low, powering down the ESP8266

Power Management Options:

• Complete Power Down: GPIO14 low after notification (recommended for battery life)
• Deep Sleep Mode: Can be configured instead of complete power down
• Continuous Operation: GPIO14 remains high for always-on operation

Power Consumption:

• Power Off State: ~0μA (ESP8266 completely powered down)
• Active Mode: ~80mA during WiFi transmission
• Battery Life: Months to years depending on event frequency and configuration

Power Input Considerations

• Only one power source can be connected at a time: USB charging, J3 (PowerIn), or UART programming connector
• Connecting multiple power sources simultaneously can damage the board
• This simple design lacks protection against multiple power source conflicts
• Always disconnect one power source before connecting another

Battery Charging Configuration

TP4056 Charger IC:

• Input Voltage: 4.5V to 5.5V (USB 5V)
• Charging Current: Configurable via RPROG resistor
• Protection Features:
  • Overcharge protection
  • Overdischarge protection
  • Overcurrent protection
  • Battery reverse polarity protection

RPROG Resistor Selection:

$$I_{charge} = \frac{V_{PROG}}{R_{PROG}} \times 1200 \quad (V_{PROG}=1V)$$

Programming & Initial Setup

Hardware Requirements

Programming Methods for ESP8266:

Option 1: TTL-to-USB Adapter

• Repository: iot-postbox/ttl_to_usb_adapter
• Purpose: Converts DTR/RTS signals to ESP8266 boot sequence
• Features:
  • Automatic boot mode selection via DTR/RTS
  • CH_PD control via dedicated jumper
  • Works with any FTDI breakout board

Option 2: Integrated USB Bridge

• Alternative: USBtoUART Bridge - Complete USB programming solution
• Advantage: Single device solution with integrated USB-to-UART conversion

Connection: UART pins populated on PCB for direct programming interface

Programming Setup:

Option 1: Using TTL-to-USB Adapter

1. Connect FTDI Breakout: Attach a USB to UART FTDI breakout board to TTL-to-USB adapter
2. Connect to PCB: Attach adapter to ESP8266 UART pins on PCB port
3. Set Boot Mode: Configure adapter jumper for programming mode
4. Upload Firmware: Use Arduino IDE or PlatformIO

Option 2: Using Integrated USBtoUART

1. Direct Connection: Connect USBtoUART bridge directly to ESP8266 UART pins
2. Automatic Boot: Device handles boot sequence automatically
3. Upload Firmware: Use Arduino IDE or PlatformIO

Firmware Configuration

Arduino IDE Setup:

// Board: "Generic ESP8266 Module" or "NodeMCU 1.0"
// Flash Size: 4MB (depending on ESP variant)
// CPU Frequency: 80MHz (recommended for power efficiency)

PlatformIO Configuration:

[env:esp8266]
platform = espressif8266
board = esp12e
framework = arduino

Initial Setup:

1. WiFi Configuration: Set network credentials in code or via captive portal
2. MQTT Settings: Configure broker address and authentication
3. Sleep Settings: Configure deep sleep duration and wake-up conditions

Interactive Bill of Materials

Technical Documentation

3D Model

Detailed Pinout Reference

Switch Sensor Inputs

Event Detection Connectors (Switch_1 & Switch_2):

Connection Notes:

• Connect switch between VCC and GPIO pins
• GPIO detects circuit closure when switch is activated
• Circuit closure triggers CH_PD wake-up sequence

Power & Charging Connectors

Battery Connector (Battery Power):

External Power Input (Main Power):

USB Charging:

• Connector: Micro-USB (depends on version)
• Input: 5V for charging and operation
• Current: Up to 1A charging (RPROG dependent)

LED Strip Connector (v0.3+)

WS2812B LED Strip (LED):

Programming & Debug Interfaces

UART Pins Extension Port (TTL_UART):