The PMW3901 is PixArt’s optical-flow chip — a tiny camera + on-chip image processor that outputs motion deltas (dx, dy in pixels per frame) over SPI. The basis for many optical-flow modules including CXOF and the Bitcraze Flow Deck.
Spec card
| Spec | Value |
|---|---|
| Resolution | 35 × 35 px |
| Field of view | 42° |
| Frame rate | up to 121 fps (full mode) |
| Sustained SPI rate | ~30-50 fps |
| Interface | SPI mode 3 |
| Power | 1.8 V (core) + 3.3 V (I/O), ~9 mA |
| Package | 6 × 7 × 2 mm |
Output
The chip provides:
- dx / dy — motion in pixels since last read.
- squal — surface quality (high = good contrast, low = featureless).
- shutter — shutter integration time (longer = darker scene).
To get velocity in m/s, you need altitude (from a rangefinder) and the FOV — velocity = dx × altitude × tan(FOV/2) / image_width / dt.
Where to go next
- Limits — operating envelope
- CXOF — ready module — production-ready alternative
- PMW3901 hub