V851S reference design · $35 class
What’s inside a $35 dashcam?
A 1440p dashcam designed around Allwinner’s V851S camera chip and modelled part by part, down to the capacitors. Each part is tagged with its basis: the chip’s datasheet, the open-source TinyVision board, or a design choice.
- Datasheet
- Reference board
- Design choice
Scroll to take it apart Drag to rotate, click a part for details Swipe sideways to rotate, tap a part for details
Two halves, four screws
The lens and vents face the road and the screen faces you; the buttons, USB-C and microSD sit on the sides. Everything that matters is on one board smaller than a credit card.
Resolution, set by the image processor
An M12 lens sits over a CMOS sensor on its own small board, linked to the main board by a MIPI CSI flex cable. In online mode the V851S image processor (ISP) handles up to 2560 × 1440, so this design records 1440p.
A camera chip in a 9 mm square
One chip runs the whole camera: a Cortex-A7 core runs Linux beside a RISC-V core, a small NPU can run detection models and a hardware encoder writes H.265 or H.264. The datasheet rates the chip for −20 to 75 °C ambient.
The memory is inside the chip
The V851S carries 64 MB of DDR2 in the same package as the processor, so the board needs no separate memory chip. The model draws the package see-through, with one block for the processor and one for the memory: a diagram, not a decapped chip. Firmware sits in a small SD NAND chip; video goes to the microSD card.
Five rails from one USB-C port
The chip’s core, its memory, its IO and the camera sensor need five voltages between them, all made on the board from 5 V; a sixth, 1.8 V, comes from an LDO inside the chip. The two buck converters and two LDOs, feedback resistors included, are the reference board’s. Input protection and the switch-over to the supercaps were added for the car.
Two choices the chip leaves to you
The V851S can drive a small screen; its sibling, the V851SE, has no display output, so picking the chip settles whether there is a screen at all. The open-source reference board is a V851SE board, so the screen is this design’s own. Backup power comes from two supercapacitors in series, which cope with heat better than a lithium cell.
Datasheet, reference board, design choice
Click a part to fly to it, or click any component on the board.
Now you take it apart
Sources: the Allwinner V851S datasheet (v1.2) and the schematic and BOM of the open-source TinyVision board, built on the V851SE.
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