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LOOK MA, NO PC!

A $55 Webcam
by Steve Freyder, David Helland, & Bruce LIghtner

Start • Hardware Design • Picking a Camera • Cheap CMOS Cameras • PicoWeb Server Hardware • Firmware Functions • Software Design • PicoWeb Firmware • Java Applet • Smile • Source and PDF

Cheap CMOS Cameras

Finally, there are several inexpensive digital cameras on the market now. These are low resolution color cameras (160 ı 120 pixels) with serial port interfaces that are generally sold as fun cameras for children. The manufacturers include Oregon Scientific (DS3838), Polaroid (FUN 320), and Mattel (Barbie Photo Designer and Nick Click). The two cameras from Mattel appear to have identical electronics inside. These cameras all seem to be based on the VVL300 digital output sensor from STMicroelectronics (formerly VLSI Vision Ltd. of Scotland).

The camera chip used in the Mattel digital cameras seems to be the STMicroelectronicsı VV6301, a highly integrated color camera sensor. A block diagram of this chip is shown in Figure 2. These chips use a CMOS imaging device rather than the typical charge-coupled device (CCD) sensor. The advantage of CMOS-based sensors is that a single silicon process can be used to manufacture the chip and all its ancillary logic. Therefore, most of the elements necessary to make a camera can be collocated on a single die, and manufactured inexpensively.

Figure 2ıThe STM VV6301 gives you everything you need to make a digital camera on one chip, including a full-color CMOS sensor array.

On the other hand, CCD-based cameras require multiple ICs and typically multiple voltages for the different IC technologies involved. The claim is that a single chip CMOS-based imager has lower noise as a result of internal parts that are in close proximity, plus on-board regulators that allow operation from a single 5-V supply. The VV6301 sensor also provides automatic black level calibration and includes a simple 2-wire I2C interface for connection to a microprocessor.

All you need to make a complete camera is a lens, memory for image storage, and a microprocessor to provide the desired camera functionality. The Mattel camera uses an Intel MCS 51 family microprocessor and static RAM for image storage.

One difference between a fun camera and a high-end digital camera is that the former depends on a PC to convert the raw pixel data into something useful (e.g., a JPEG image), and the latter does this inside the camera. Typically, there is no image compression done in the fun cameras. You only get uncompressed, raw image sensor data out the serial port. As you will see, raw pixel data needs a bit of processing to yield an image that can be viewed on a web page.

Mattelıs cameras send a total of 20 KB of raw pixel data per photo. When converted into a compressed JPEG image, this same photo is typically only one-tenth this size.

There was no question that we couldnıt do any useful image processing in the PicoWebıs tiny microcontroller. However, we still had a trick up our sleeves!

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