A portable, battery-powered camera unit contains a programmable digital camera that is implemented on a single chip utilizing active-pixel-sensor (APS) technology, plus circuitry for digital radio communication between the camera and a base station. A laboratory-bench-top version of this digital wireless camera has been demonstrated to function as intended, and continuing development efforts are directed toward miniaturization (see figure). The fully miniaturized unit is intended to serve as a prototype of low-power, long-battery-life, portable, digital, wireless electronic cameras for such applications as surveillance in military and civilian settings, home security, and remote monitoring of babies.

The Digital Wireless Camera will eventually occupy a volume of only about 2 in.^3 (≈33 cm^3).

The APS-camera portion of the circuitry was described in "Active-Pixel-Sensor Digital Camera on a Single Chip" (NPO-20262), NASA Tech Briefs, Vol. 22, No. 10 (October 1998), page 44. To recapitulate: A complementary metal oxide/semiconductor (CMOS) integrated-circuit chip contains a 256 × 256 photogate APS sensor array, 256 on-chip analog-to-digital converters (ADCs) to digitize the pixel data, timing and control circuitry, and four digital-to-analog converters (DACs) to provide the analog references necessary for the imager and ADCs. From an external source (the base station), the chip can be programmed to perform a variety of imaging operations; for example, to obtain a desired exposure time and/or to operate in any of a number of imaging modes to reduce power consumption; for example, windowing, subsampling. The chip can also be programmed to establish a required digital interface configuration; this feature affords flexibility for integration with a variety of base-station digital systems. The total power consumption of this portion of the camera (that is, the camera without the radio-communication portion of the circuitry) is of the order of tens of milliwatts in full operation. After obtaining an image or set of images, the camera chip automatically enters a low-power idle mode where it uses about 40 µW of power. In contrast, a typical charge-coupled-device (CCD) camera circuit with analog output consumes 1 to 2 W when turned on, and cannot be commanded to operate in multiple lower-power modes.

The camera communicates with the base station over a bidirectional radio link, with a range of about 1 km. The camera transmits video data to the base station at a rate of 2.455 Mb/s at a carrier frequency of 2.4216 GHz and receives command data at a rate of as much as 2.4 kb/s at a carrier frequency of 418 MHz. Spread-spectrum modulation is used to reduce the probability of interception. In an attempt to minimize the power consumed by the camera and maximize the communication link efficiency, convolutionally-encoded binary phase shift keying (BPSK) is used for coding and modulation, together with a coherent detection receiver at the base station. By use of half-duplex protocols, the base station can communicate with as many as 254 such cameras. The miniature low-power communication system can be extended to be used with other sensor systems.

This work was done by Martin Agan, Eric Fossum, Robert Nixon, Brita Olson, Bedabrata Pain, Christopher Pasqualino, Ed Satorius, Timothy Shaw, and Gary Stevens of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Electronics & Computers category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to: Technology Reporting Office JPL Mail Stop 122-116 4800 Oak Grove Drive Pasadena, CA 91109 (818) 354-2240 Refer to NPO-20331, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).
Miniature, low-power, digital, wireless electronic camera

(reference NPO-20331) is currently available for download from the TSP library.

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This article first appeared in the March, 2000 issue of NASA Tech Briefs Magazine.

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