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May 25, 2025 13:16
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Aliexpress E88 drone Optical Flow module protocol reverse engineering
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| #!/usr/bin/env python3 | |
| import serial | |
| import time | |
| import struct | |
| # ------------------ | |
| # Configuration | |
| # ------------------ | |
| SERIAL_PORT = '/dev/ttyUSB0' | |
| BAUD_RATE = 115200 | |
| SYNC_HEADER = b'\x99\x77\x0e' # 3-byte header | |
| FRAME_SIZE = 13 # total bytes per frame | |
| def extract_frames(buffer: bytes) -> tuple[list[bytes], bytes]: | |
| """ | |
| Extract all 13-byte frames that start with 99 77 0E from 'buffer'. | |
| Returns (list_of_frames, leftover_bytes). | |
| """ | |
| frames = [] | |
| i = 0 | |
| while i <= len(buffer) - FRAME_SIZE: | |
| if buffer[i:i+3] == SYNC_HEADER: | |
| candidate = buffer[i:i+FRAME_SIZE] | |
| frames.append(candidate) | |
| i += FRAME_SIZE | |
| else: | |
| i += 1 | |
| leftover = buffer[i:] | |
| return frames, leftover | |
| def decode_frame(frame: bytes): | |
| """ | |
| Attempt to interpret the 13-byte frame as: | |
| header[0..2] = 0x99 0x77 0x0e | |
| data[3..4] = deltaX (signed 16-bit, little-endian) | |
| data[5..6] = deltaY (signed 16-bit, little-endian) | |
| data[7] = quality? (8-bit) | |
| data[8..12] = always zero in your logs | |
| Returns a dict with the decoded fields. | |
| """ | |
| # sanity check: must be 13 bytes total | |
| assert len(frame) == FRAME_SIZE, "Frame is not 13 bytes" | |
| xr = frame[3:5] # 2 bytes | |
| yr = frame[5:7] # 2 bytes | |
| d3 = frame[7] # 1 byte | |
| qual = d3 / 255.0 | |
| # Little-endian signed 16: | |
| (x,) = struct.unpack('<h', xr) | |
| (y,) = struct.unpack('<h', yr) | |
| xw = x * qual | |
| yw = y * qual | |
| return [x, y, d3] | |
| def main(): | |
| print(f"Opening {SERIAL_PORT} at {BAUD_RATE} baud...\n") | |
| ser = serial.Serial(SERIAL_PORT, BAUD_RATE, timeout=0.1) | |
| buffer = b'' | |
| xsum = 0 | |
| ysum = 0 | |
| print("Reading data and decoding frames (Ctrl+C to stop)...\n") | |
| try: | |
| while True: | |
| chunk = ser.read(ser.in_waiting or 1) | |
| if chunk: | |
| buffer += chunk | |
| frames, buffer = extract_frames(buffer) | |
| for f in frames: | |
| decoded = decode_frame(f) | |
| hex_frame = ' '.join(f'{b:02X}' for b in f) | |
| xsum+=decoded[0] | |
| ysum+=decoded[1] | |
| print(f" Decoded:\t X: {decoded[0]}\t " | |
| f"Y: {decoded[1]}\t\t " | |
| f"Xsum: {xsum}\t\t " | |
| f"Ysum: {ysum}\t\t " | |
| f"?: {decoded[2]}\t ") | |
| time.sleep(0.01) | |
| except KeyboardInterrupt: | |
| print("\nUser interrupted. Stopping...\n") | |
| finally: | |
| if ser.is_open: | |
| ser.close() | |
| print("Serial port closed.") | |
| if __name__ == "__main__": | |
| main() |
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