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Optical flow sensor · FD-FLOW-LITE
Fiodel Optical Flow Lite
Optical flow and a laser rangefinder on one 20 × 16 mm board, for position hold without GPS.
Expected price
Coming soon — in development
Not on sale yet. Its specifications are from the design and may change before release.
Tell me when it is readyOn WhatsApp. We will message you when pre-orders open.
- PixArt PMW3901 optical flow sensor, works from 80 mm up
- ST VL53L4CX laser rangefinder, up to 6 m indoors
- STM32G431 at 170 MHz runs both sensors
- One UART for Betaflight, iNav, ArduPilot and PX4
- Mode button and green status LED
- Firmware updates over the same 4-pin plug
- 20 × 16 mm, ships in a printed case
Questions about it? Ask us on WhatsApp
Overview
The Fiodel Optical Flow Lite is a downward-facing sensor for holding position where GPS cannot help: indoors, under cover and close to the ground. A PixArt PMW3901 watches the ground move beneath the drone, and an ST VL53L4CX time-of-flight laser measures the height above it. Together they tell the flight controller how far the drone has drifted and how high it is.
An STM32G431 reads both sensors and sends their data to the flight controller on one UART through a 4-pin JST-SH plug. It is being designed to run one firmware for Betaflight (2026.6 and newer, through its built-in UPT1 driver), iNav (MSP) and ArduPilot and PX4 (MAVLink). A button on the board selects the mode, and Betaflight switches it over by itself when it connects.
The board is 20 × 16 mm, six layers, with both optics on one face. It takes 5 V from the flight controller (a 4.5 V serial-socket supply is enough) through reverse-polarity and surge protection, and it ships in a printed case marked with its pins and the forward direction.
Layout
Top side
- AControllerSTM32G431
- BMode button
- CFlight-controller plugJ1 · JST-SH 4-pin, 1.0 mm
- DStatus LED
Bottom side
- ALaser rangefinderVL53L4CX
- BOptical flow sensorPMW3901
Specifications
Optical flow
| Sensor | PixArt PMW3901 |
|---|---|
| Working distance | 80 mm and up |
| Field of view | 42° |
| Maximum speed | 7.4 rad/s |
| Minimum light | 110 lux |
Rangefinder
| Sensor | ST VL53L4CX time-of-flight, 940 nm |
|---|---|
| Range, white target | Up to 6.0 m indoors, 1.8 m outdoors under an overcast sky |
| Range, grey target | Up to 2.5 m indoors, 1.3 m outdoors under an overcast sky |
| Closest | 10 mm |
| Accuracy | ±3 % indoors above 110 mm |
| Measurement time | 33 ms |
Controller and output
| Processor | STM32G431, 170 MHz Cortex-M4F |
|---|---|
| Interface | UART, 4-pin JST-SH |
| Flight software (planned) | Betaflight 2026.6 and newer, iNav, ArduPilot, PX4 |
| Protocols (planned) | Betaflight UPT1, MSP (iNav), MAVLink (ArduPilot and PX4) |
| Mode | Set with the button, or by Betaflight automatically |
| Firmware update | Over the 4-pin plug |
Power
| Input | 5 V (runs from a 4.5 V flight-controller rail) |
|---|---|
| Protection | Reverse-polarity diode and TVS on the input |
| Regulators | TI 3.3 V and 1.9 V LDOs |
| Operating temperature | 0–40 °C |
Board
| Size | 20 × 16 mm |
|---|---|
| Construction | 6-layer, 1.0 mm, ENIG finish, black solder mask |
| Mounting | 4 × M2 holes |
| Housing | Printed case, pins and forward arrow marked |
| Indicators | Green status LED |
Pinout
J1Flight-controller plugJST-SH 4-pin, 1.0 mm
| Pin | Signal | Detail |
|---|---|---|
| 1 | 5 V in | |
| 2 | GND | |
| 3 | TX | Sensor → flight controller RX |
| 4 | RX | Sensor ← flight controller TX |
Questions
- Which flight controllers will it work with?
- Any that runs Betaflight 2026.6 or newer, iNav, ArduPilot or PX4 and has a free UART. On Betaflight and iNav it uses four wires; ArduPilot and PX4 take it on a telemetry port in MAVLink mode.
- Does it work in the dark?
- The rangefinder does. The optical flow sensor needs at least 110 lux on the ground beneath it, about the light of a dim room.
- How is the firmware updated?
- Over its own 4-pin plug: holding the button while powering up puts it in update mode.
- When can I buy it?
- The board is designed and its firmware is being written. The price shown is what we expect to charge. Ask us on WhatsApp and we will tell you when pre-orders open.
Goes with this board
Flight controller
Fiodel F405 Flight Controller
STM32F405 · ICM-42688-P · 6S · 30.5 mm
Plugs into one of its 4-pin serial sockets with a straight cable.
