Document Camera

Overview

A document camera is the modern replacement for the overhead projector: a video camera on an arm, pointed down at the desk, sending a live image to a projector, display, or computer. Unlike a flatbed scanner it shows things as they happen, handwriting, dissections, circuit boards under test, a watch movement being assembled, and unlike a transparency projector it images any opaque object.

The signal chain is short. The Camera Head captures the scene on a 13 MP CMOS Image Sensor behind a zoom Lens Assembly; the Main Processing Board turns raw sensor data into corrected 4K video; the Video Output Board hands that video to the outside world over HDMI and USB. The Articulated Arm and weighted Base Unit are what make it usable: the head holds any pose over the desk and the whole unit folds flat for a briefcase.

Camera head

The head packs the optics of a small camcorder. The 1/2.7-inch CMOS CMOS Image Sensor sits behind an IR-Cut Filter, without the filter, infrared leaking through the lens would tint paper magenta and shift ink colours. The Lens Assembly provides modest optical zoom, extended losslessly in the digital domain by cropping the 13 MP frame, for about 10× combined. Focus is continuous: the Autofocus Actuator drives the focusing group whenever the contrast metric drops, so the image stays sharp as the presenter swaps a flat page for a 30 cm object.

The Head Housing rotates with detents at 0° and 90°, letting the same camera shoot the desk, the room, or the presenter. An electret Microphone in the head picks up narration for USB recording and conferencing.

Arm and base

The Upper Arm Segment and Lower Arm Segment are hollow aluminium extrusions joined by three Friction Hinge units. Each hinge is a preloaded clutch-washer stack delivering constant torque: stiff enough to hold the head against gravity at full 40 cm extension, loose enough to reposition one-handed, with no levers to lock. The Head Swivel Joint at the end adds independent pan and tilt. The camera harness, a Wire Bundle carrying sensor data at multiple gigabits per second, runs inside the arm, held by Cable Clips positioned so the cable bends at the hinge axes rather than being stretched across them; this is what survives thousands of fold cycles.

All of that cantilevered mass is balanced by the Base Casting, a steel-weighted plate of about a kilogram on Anti-Slip Feet. The base also carries the controls: a Control Button Membrane for autofocus trigger, image freeze, rotation, and lamp control, plus the Zoom Rocker and Power Button.

Lighting

Room light is the enemy of a downward-facing camera, the presenter's hand and the arm itself throw shadows across the page. The LED Lighting panel solves this with a row of high-CRI white LEDs (LED Array) beside the lens, shining down the same axis the camera looks along, so shadows fall away from the lens line of sight. The LED Diffuser spreads the output to prevent specular hot spots on glossy textbook pages, and a Power MOSFET driver steps brightness from the membrane panel. Colour temperature near 5600 K keeps white balance consistent whether the room is lit by daylight or fluorescents.

Processing and output

On the Main Processing Board, a video Compute SoC Module runs the image signal processor: demosaicing, lens-shading correction, auto exposure, auto white balance, and the autofocus loop. Document cameras add modes a camcorder lacks, a text-enhancement curve that crushes paper texture and sharpens strokes, one-touch 90°/180° rotation for upside-down documents, and image freeze so the presenter can swap pages without the audience watching. A small Microcontroller supervises power, buttons, and the LED driver.

The Video Output Board presents the outputs on the rear panel through standard Connector hardware: HDMI out to the projector, an HDMI passthrough input so a laptop can share the same projector without recabling, and USB-C. The USB port enumerates as a standard UVC webcam, so the device works in any conferencing or recording application with no driver. Power arrives through a 12 V barrel jack from the external Power Supply, or over USB-C PD when driving only the USB output.