esp8266-weather-clock-opensource/docs/HARDWARE.md

Hardware Documentation

Device Specifications

Original Product

• Name: ESP8266 Mini Weather Clock Kit
• Model: TJ-56-654
• Source: AliExpress Link
• Price: ~$12 USD
• Dimensions: 40mm x 40mm x 43mm

Components

ESP-01S WiFi Module

• Chip: ESP8266EX
• Flash: 1MB (8Mbit)
• RAM: 80KB total (32KB instruction, 48KB data)
• CPU: 80MHz (can be overclocked to 160MHz)
• WiFi: 802.11 b/g/n (2.4GHz only)
• GPIO: 2 usable pins (GPIO0, GPIO2)
• Voltage: 3.3V (NOT 5V tolerant!)

Display Module

• Model: GM009605v4.3
• Type: OLED (Organic LED)
• Resolution: 128x64 pixels
• Size: 0.96 inches diagonal
• Controller: SSD1306 or SH1106 compatible
• Interface: I2C
• I2C Address: 0x3C (default), 0x3D (fallback)
• Colors: Monochrome (white on black)

Power Supply

• Input: 5V via Micro-USB
• Regulator: Onboard 3.3V LDO (on main PCB)
• Current: ~80-120mA typical

Case

• Material: Transparent acrylic
• Pieces: 6 (top, bottom, 4 sides)
• Assembly: Brass standoffs and M2.5 screws

Pinout

ESP-01S Pin Configuration

┌─────────────────┐
│  ESP-01S Module │
├─────────────────┤
│                 │
│  [antenna]      │
│                 │
│  3V3 │ │ GND    │
│   TX │ │ GPIO0  │  ← I2C SDA (custom mapping!)
│   RX │ │ GPIO2  │  ← I2C SCL (custom mapping!)
│   EN │ │ GND    │
│                 │
└─────────────────┘

Pin Functions

Pin	Standard Use	This Project
3V3	Power (3.3V)	Power
GND	Ground	Ground
TX	UART TX	Serial debug output
RX	UART RX	Serial input (flashing)
GPIO0	General I/O	I2C SDA (data line)
GPIO2	General I/O	I2C SCL (clock line)
EN	Chip Enable	Pulled high (always on)

⚠️ Important: This project uses non-standard I2C pin mapping!

• Typical ESP8266: SDA=GPIO4, SCL=GPIO5
• This device: SDA=GPIO0, SCL=GPIO2

I2C Connection

ESP-01S          OLED Display
─────────────────────────────
3V3      →       VCC
GND      →       GND
GPIO0    →       SDA
GPIO2    →       SCL

Programming Connection (FTDI)

FTDI Adapter     ESP-01S
──────────────────────────
3V3      →       3V3
GND      →       GND
TX       →       RX
RX       →       TX
GND      →       GPIO0  (boot mode - connect only during programming)

Programming Mode:

1. Connect GPIO0 to GND
2. Power on the ESP-01S
3. Remove GPIO0-GND connection
4. Upload firmware
5. Power cycle to run new code

PCB Layout

The main PCB (TJ-56-654) contains:

• ESP-01S socket (8-pin header)
• OLED display connector (4-pin header)
• 3.3V voltage regulator (AMS1117-3.3)
• Micro-USB connector for power
• Bypass capacitors

Memory Map

Flash Memory (1MB)

0x00000000 - 0x00010000  : Bootloader (64KB)
0x00010000 - 0x0007C000  : Firmware (~470KB max for OTA)
0x0007C000 - 0x00080000  : EEPROM emulation (16KB)
0x00080000 - 0x000FA000  : OTA partition (~470KB)
0x000FA000 - 0x000FB000  : WiFi config (4KB)
0x000FB000 - 0x00100000  : System reserved (20KB)

RAM Layout

Total: 80KB
├── IRAM (Instruction): 32KB
│   ├── Used: ~62KB (94%)  ← Critical!
│   └── Free: ~4KB
└── DRAM (Data): 48KB
    ├── Heap: ~40KB free
    ├── Stack: ~4KB
    └── Globals: ~4KB

Power Consumption

Mode	Current	Power @3.3V
Active (WiFi on)	80-120mA	264-396mW
Display on	+15mA	+50mW
Deep sleep	~20µA	~66µW

Note: This firmware does not use deep sleep (clock is always-on).

Hardware Modifications

Optional Improvements

1. External antenna: Solder U.FL connector for better WiFi range
2. Temperature sensor: Add DHT22 or BME280 to GPIO (requires software changes)
3. Buttons: Add physical buttons for display control (requires free GPIO)
4. Battery backup: Add 18650 cell + TP4056 charger for UPS functionality

Pin Availability

ESP-01S has very limited GPIO:

• GPIO0: Used for I2C SDA (can't use for other purposes)
• GPIO2: Used for I2C SCL (can't use for other purposes)
• TX/RX: Can be repurposed (breaks serial console)

For additional peripherals, consider upgrading to ESP-12F or ESP32.

Troubleshooting

Display not working

• Check I2C address: Try 0x3C and 0x3D
• Verify pin mapping: SDA=GPIO0, SCL=GPIO2
• Check power: Display needs 3.3V
• Test with I2C scanner (/api/i2c-scan)

WiFi connection fails

• ESP8266 only supports 2.4GHz (not 5GHz)
• Check power supply: Weak USB port can cause brownouts
• Some routers don't like ESP8266 - try different channel

Bootloop/crashes

• Check IRAM usage: Must be <95%
• Verify flash mode: Should be "DIO" not "QIO"
• Bad power supply: Use quality USB cable

Can't flash firmware

• GPIO0 must be LOW during boot for programming mode
• Some FTDI adapters need DTR/RTS wiring for auto-reset
• Baud rate: Try 115200 (default) or 57600 if errors

Datasheets

• ESP8266EX Datasheet
• ESP-01S Pinout
• SSD1306 OLED Controller

Safety Warnings

⚠️ Do NOT connect 5V to ESP-01S GPIO pins - they are NOT 5V tolerant!

⚠️ Use 3.3V FTDI adapter - 5V will permanently damage the ESP8266

⚠️ Check polarity - Reversing power can destroy the module

⚠️ ESD sensitive - Touch grounded metal before handling board