Witness Camera circuit

The Witness Camera operation is conceptually simple, but involves many ingredients. Some are physical components, the others are software blocks. To make things clear, I will introduce them gradually, according to the operating mode.

The most important hardware component is the ITC328 camera module. It consists of a VGA (640×480) CMOS colour sensor and a JPEG-compression chip. The compression engine includes a serial interface at 3.3V levels that can be connected directly to a microcontroller’s UART. Issuing the appropriate commands you can take snapshots as JPEG-compressed byte streams. The camera comes in a handy module with everything including the lens, and a 4-pole connector for power and data.
The most important software component is the AVR-DOS file system. It is a library for driving mass storage devices, like SD and MMC cards, CompactFlash, and even hard disks connected to the AVR microcontroller. It provides an high-level programming interface for accessing disks formatted according to FAT16 or FAT32 specifications, which means its files are directly compatible with PCs. By linking AVR-DOS to your program you can create and open files, write and read data, create and change directories with simple commands, like you would do on a PC. Restricting read/write access to one file at a time, the FLASH and RAM footprints are minimal (8kB and 1.3kB), making it possible to use a small 8-bit AVR device like the Mega32 for tasks usually accomplished by 16- or even 32-bit processors.

These two blocks are the foundation and starting point of the Witness Camera design. With the aid of the simplified block diagram of Figure 1, let’s see how these block interoperate during normal operation as a time-lapse recorder.[...]