The flight controller pinout diagram is the single most important document for a drone build. Read it wrong and you'll spend an afternoon chasing a problem that's actually two crossed wires. This guide walks through every annotation you'll encounter on a modern FC diagram.
Orientation: Which Way Is Up?
Pinout diagrams almost always show the board from the top — the component side. The silkscreen arrow on the board itself indicates the forward direction (positive X axis). Before reading any pad labels, orient the diagram to match the board's physical orientation as it will be mounted in the frame.
Power Pads
Every FC has a primary power input. You'll see:
- VBAT — raw battery voltage in (4S = up to 16.8 V; 6S = up to 25.2 V). Always check the max voltage rating of your FC before connecting a high-cell-count pack.
- GND — battery negative. Often multiple GND pads distributed around the board for current sharing.
- 5V or VOUT — 5 V BEC output. Used to power peripherals. Check the current rating — many FCs provide only 500 mA–1 A, which limits what you can hang off it.
- 4V5 — some FCs expose 4.5 V (USB voltage minus drop). This is NOT a 5 V pad. Don't power a VTX from it.
- 3V3 — 3.3 V regulated output. For sensors and receivers that require 3.3 V logic.
- 9V or 12V — video transmitter supply on some all-in-one stacks.
UART Ports — The TX/RX Convention
This is where most wiring mistakes happen. UART labels are from the FC's perspective, not the peripheral's:
- FC TX → peripheral RX
- FC RX → peripheral TX
The FC is transmitting on TX, so the other device receives it on its RX. Always cross the lines. A GPS module that never locks is often a crossed TX/RX issue.
UARTs are numbered (UART1, UART2, etc.) and may appear as T1/R1, TX1/RX1, or just 1T/1R depending on the manufacturer. Betaflight assigns each peripheral to a UART port in the Ports tab — match the physical UART number to the configurator port number.
Motor Pads
Motor pads are labelled M1–M4 (quad) or M1–M8 (larger configurations). The diagram should show a top-down frame diagram with motor positions. Verify motor order matches your flight controller firmware's expected configuration — Betaflight Quad X, ArduPilot, and KISS all use different numbering.
Special Function Pads
| Pad label | Function | Common connection |
|---|---|---|
| CURR | Analog current sensor input | Current sensor shunt output (0–3.3 V) |
| RSSI | Receiver signal strength (analog) | Receiver RSSI output |
| CAM | FPV camera video input | Camera video signal |
| VTX | Video transmitter video output | VTX video input |
| SA | SmartAudio VTX control | VTX SmartAudio data pin |
| SDA / SCL | I²C data / clock | External GPS compass, barometer |
| BOOT | DFU mode button | Held during power-on for firmware flash |
| LED | LED strip data output | WS2812B addressable LEDs |
| BUZZ | Buzzer output | Passive buzzer for lost model alarm |
Reading the Diagram Top-to-Bottom
A systematic approach when building:
- Find VBAT and GND first — confirm they match your ESC/PDB output pads.
- Identify which UART you'll use for the receiver. Map it in Betaflight before wiring.
- Identify motor pads M1–M4 and confirm the motor order diagram matches your frame layout.
- Find the camera (CAM) and VTX pads — these are usually along one edge.
- Identify any remaining UART for GPS if needed.
- Note which 5 V pad is rated highest — use it for the hungriest peripheral.
The full UART tracing technique is covered in detail in Module 2, Lesson 3 of the course.