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LamaPLC: CJMCU-3901/PMW-3901 compact optical flow sensor module/IC by PixArt with SPI communication
The CJMCU-3901 is a compact optical flow sensor module that integrates the PixArt PMW3901 chip. It is mainly designed for X-Y motion detection and precise positioning in drones and robotics, particularly in indoor or GPS-denied settings.
Key Technical Specifications
- Sensor: PixArt PMW3901MB-TXQT.
- Operating Voltage: 1.8V to 3.6V (typically used at 3.3V).
- Operating Range: 80mm to infinity (no lens adjustment required).
- Interface: 4-wire SPI (up to 2MHz).
- Power Consumption: Very low, typically less than 9mA in active mode.
- Field of View (FOV): Approximately 40°.
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CJMCU-3901 pinout
| Pin Name | Function | Description |
|---|---|---|
| 3V3 | Power Supply | Typically 3.3V (range: 1.8V – 3.6V) |
| GND | Ground | Connect to the common ground of your system |
| MOS | SPI Data In | Master Out Slave In; receives commands from the controller |
| CLK | SPI Clock | Serial clock signal generated by the master |
| MIS | SPI Data Out | Master In Slave Out; sends motion data to the controller |
| CS | Chip Select | Active-low signal to enable the sensor for communication |
| RST | Reset | Optional active-low hardware reset pin |
| MOT | Interrupt | Motion detection output; triggers when new motion is detected |
| VRE | reference voltage output | It provides access to the sensor's internal regulated voltage, which is used as a reference for its internal optoelectronic operations |
Connection Requirements
- Logic Levels: This sensor uses 3.3V logic. If you are using a 5V microcontroller, such as an Arduino Uno, you must use a level shifter to prevent damage to the chip.
- SPI Speed: The module supports SPI clock speeds up to 2 MHz.
- Orientation: Look for a small notch or arrow on the board; this usually indicates the “back” or “front” to ensure correct X-Y coordinate tracking in your firmware.
Arduino wiring
Since the CJMCU-3901 operates on 3.3V logic, you must use a 3.3V Arduino (e.g., Nano 33 IoT) or a level shifter if using a 5V Arduino (e.g., Uno).
| CJMCU-3901 Pin | Arduino Pin (Uno/Nano) | Function |
|---|---|---|
| VCC | 3.3V | Power Supply |
| GND | GND | Ground |
| CS | D10 (or any Digital Pin) | Chip Select |
| MOSI | D11 | SPI Data In |
| MISO | D12 | SPI Data Out |
| SCLK | D13 | SPI Clock |
Arduino code
Need to install the Bitcraze_PMW3901 library via the Arduino Library Manager.
#include "Bitcraze_PMW3901.h" // Using digital pin 10 for chip select Bitcraze_PMW3901 flow(10); void setup() { Serial.begin(9600); // Initialize the sensor if (!flow.begin()) { Serial.println("Initialization of the flow sensor failed"); while(1); // Halt if sensor not found } } int16_t deltaX, deltaY; void loop() { // Get motion count since the last call flow.readMotionCount(&deltaX, &deltaY); Serial.print("X: "); Serial.print(deltaX); Serial.print(" | Y: "); Serial.println(deltaY); delay(100); // Small delay for readability }Operational Notes
- Measurement Units: The sensor outputs unitless “ticks” representing the amount of motion.
- Surface Texture: The sensor requires a textured surface (not solid black or mirrored) to track movement effectively.
- Focus: The built-in lens is typically pre-focused from 80mm to infinity.
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