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

The IoT-PostBox firmware is built using the Arduino-ESP8266 framework and PlatformIO. Depending the ESP8266 module used (ESP-12F or ESP-07S), you will need to select the appropriate board environment. Further instructions and documentation can be found in the Firmware page.

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):