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Issue #202 May 2007
The Witness Camera
Build a Self-Recording Surveillance Camera
Grand Prize Atmel AVR Design Contest 2006
by Alberto Ricci Bitti
If burglars try to break into Alberto’s house, all of their movements will be recorded by his self-recording camera system. This is no ordinary alarm detector. The well-designed system silently starts recording when it senses movement.
Start | Solid-State Recording | Full Interaction | Complete Picture | Basic Instinct | Filled To Capacity | Speech Preparation | Circuit Implementation | Concept To Prototype | Picture Inspection |Design Evolution | Sources & PDF
I always wanted a video recording system to monitor my house, but commercially available surveillance systems didn’t meet my needs. Price tag aside, most aren’t designed for home use. Very few houses have a burglarproof place for the time-lapse recorder and monitor. In addition, wires running to the cameras can ruin your décor. RF-linked cameras are not an option if you care about your privacy and your Wi-Fi network. Even network cameras, when used for continuous recording, can easily eat up most of your wireless bandwidth.
The Witness Camera is my solution to these problems. It is a combination of a VGA CMOS camera, a passive infrared movement sensor, a gigabyte-class Secure Digital (SD) card, and an Atmel ATmega32 microcontroller implementing a solid-state time-lapse recorder (see Photo 1). My prototype looks like an ordinary alarm detector, but when it detects movement, it silently starts recording. An external trigger or an interval timer can also start the recording process, or it can be continuous.
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| Photo 1—The Fantastic Four: the VGA-JPG camera, the 1-GB flash memory card, the ATmega32 microcontroller, and the PIR movement sensor. There are also “invisible” software parts, like the AVR-DOS file system that drives the card. |
I designed the camera to be a complete, compact, self-contained surveillance system (see Photo 2). It is designed with home users in mind. The hardware, which is surprisingly simple and affordable, requires only a handful of inexpensive parts and can be installed in minutes wherever there is a mains plug. An IR remote and interactive voice prompts allow easy set up and operation, even when the camera is concealed or installed in places like ceiling corners.
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| Photo 2a—The prototype looks great. I placed it in a standard 100 x 130 mm DIN rail-switch enclosure. b—The PCB protrudes slightly out of the box walls for card extraction. A detector switch senses lid openings, terminating pending disk writes, and activating the tamper relay. When the green LED fires, it’s safe to remove the card. |
Equipped with a 1-GB card, the system can take about 50,000 color pictures at 320 × 200 pixels (comparable to VHS-CCTV recorders) or 25,000 at 640 × 480 pixels. A new frame is taken every 2 to 5 s. When the card is full, new pictures automatically replace older ones.
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