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Hardware Wiring Guide

Connect NodeMCU (ESP8266) and Pro Micro (ATmega32U4) via serial communication. NodeMCU is powered by Pro Micro - only ONE USB cable needed.

Connected Hardware Example

Connection Table

Core Connections (Required)

NodeMCU Pin Pro Micro Pin Wire Color Description
Vin VCC Red Power (5V)
GND GND Black Common ground
TX RX (Pin 0) Yellow/White Serial TX→RX
RX TX (Pin 1) Orange/Green Serial RX→TX

Important: TX/RX must be crossed (not straight-through)!

Optional Display Connections

Display Pin NodeMCU Pin Wire Color Description
VCC 3.3V Red Power (3.3V)
GND GND Black Common ground
SDA D3 (GPIO4) Blue/Green I2C data
SCL D4 (GPIO5) Yellow/White I2C clock

Don't use D0 - GPIO16 doesn't support I2C!

Wiring Diagram

Core Connections

Pro Micro          Wire Color        NodeMCU
─────────          ──────────        ───────
VCC (5V out)  ───────[RED]─────────> Vin (5V in)
GND           ──────[BLACK]─────────> GND
TX (Pin 1)    ─────[ORANGE]────────> RX
RX (Pin 0)    <────[YELLOW]───────── TX
    │
   USB
    │
 Computer
(Power + HID)

Optional Display Connections

NodeMCU           Wire Color        OLED Display
───────           ──────────        ────────────
3.3V          ───────[RED]─────────> VCC
GND           ──────[BLACK]─────────> GND
D3 (GPIO4)    ─────[BLUE/GREEN]────> SDA (I2C Data)
D4 (GPIO5)    ────[YELLOW/WHITE]───> SCL (I2C Clock)

Step-by-Step Instructions

Core Setup (Required)

  1. Disconnect both devices from USB
  2. Connect 4 wires:
    • Red wire: Pro Micro VCC → NodeMCU Vin
    • Black wire: Pro Micro GND → NodeMCU GND
    • Yellow wire: NodeMCU TX → Pro Micro RX (Pin 0) (crossed!)
    • Orange wire: NodeMCU RX → Pro Micro TX (Pin 1) (crossed!)
  3. Double-check connections - especially that TX/RX are crossed
  4. Connect Pro Micro to computer via USB - powers both devices

Optional: OLED Display Setup

If using a 128x64 I2C OLED display, connect 4 additional wires:

  • Red wire: NodeMCU 3.3V → Display VCC
  • Black wire: NodeMCU GND → Display GND
  • Blue/Green wire: NodeMCU D3 (GPIO4) → Display SDA
  • Yellow/White wire: NodeMCU D4 (GPIO5) → Display SCL

Important: Use 3.3V (not Vin/5V) to power the display!

Power Notes

  • Single USB cable powers both devices (Pro Micro → computer)
  • NodeMCU powered via VCC→Vin connection
  • Total consumption: ~350-400mA (safe for USB 2.0/3.0)
  • Use quality USB cable for reliable power
  • If power issues occur, try USB 3.0 port or powered hub

Setup Options

  • Breadboard: Easy to modify, good for testing, no soldering
  • Direct wiring: More compact, fewer components
  • Permanent: Solder connections, use perf board, add case

Common Mistakes

❌ TX/RX straight-through - Must be crossed (TX→RX, RX→TX) ❌ Missing GND - Communication won't work without common ground ❌ Missing VCC→Vin - NodeMCU won't power on ❌ Using 3.3V instead of VCC - Insufficient power ❌ Both USB cables connected - Only Pro Micro needs USB ❌ Wrong serial pins - Use Pro Micro pins 0 (RX) and 1 (TX), not USB serial

Troubleshooting

  • NodeMCU won't power on: Check VCC→Vin connection. Try different USB port/cable.
  • No communication: Verify TX/RX are crossed. Check GND connection. Upload code to both devices.
  • Intermittent issues: Usually power-related. Try USB 3.0 port or powered hub.
  • NodeMCU resets randomly: Insufficient power. Use better USB cable or powered hub.

Safety

  • Disconnect USB before changing wiring
  • Never connect output pins together (VCC to VCC)
  • NodeMCU may get warm during WiFi operation (normal)
  • If components get hot, disconnect immediately

See SETUP.md for software setup instructions.