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Under the Hood: Surveillance on a shoestring

A recent run-through of my local Fry's Electronics was stretched a bit when I took a walk down the do-it-yourself security aisle. Among an array of products for those wanting self-serve video monitoring, a $99.99 surveillance kit caught my eye.

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A hundred bucks for a two-camera, one-basestation, 2.4-GHz wireless audio/ video monitoring setup–capable of near-zero-light operation, given the product's built-in infrared (IR) illumination ring with each camera–seemed like an impressive deal.

Branded as the SecurityMan NiteCam2, the design is a re-badged product from Shenzhen AEE Wireless.

The product is simple to set up. Each of the two weather-resistant, microphone-equipped bullet cameras needs only an ac outlet for an adapter to transmit audio and color video back to a single basestation.

The industrial, scientific and medical (ISM) 2.4-GHz bands used by the cameras are established via a DIP switch on the base unit, and output from the base is via RCA-jack composite video and monaural audio for use with any TV monitor. A 100-meter range in clear line of sight is claimed, but you can bank on something far less in a real-world installation.

The cameras contain the lensed imager, microphone and RF transmission circuitry, along with a ring of IR LEDs to provide human-invisible flood illumination for nighttime use. AEE claims 5-lux minimum visible-light illumination and 0-lux (with IR on) sensitivity to 7 meters.

Transmission signals come over 2414-, 2432-, 2450- or 2468-MHz center frequencies (18-MHz channel separation) for some combination of multicamera utility and simple interference avoidance.




An Omnivision OV7930 provides 510 x 492 NTSC video output directly, handling everything from raw image collection to gain control, auto color balance and NTSC formatting/conversion.

The camera electronics consist of a BJX (Shenzhen Bojuxing Industrial Development) BJ8P153 8-bit MCU ROM controller and RichWave RTC6701 CMOS 2.4-GHz FM/FSK (frequency-shift-keying) transmitter running at 10 mW of RF output power.

Although the RichWave part supports digital FSK capability, the design uses only the device's simpler analog RF frequency-modulation (FM) function to up-convert the NTSC output of the Omnivision image sensor. A simple wire antenna delivers RF from a stub protruding out the rear of the camera.

With a less-sophisticated FM scheme, there is relatively little protection against outside interferers in the increasingly crowded ISM band. Lacking the ultratight channels, error-correction and/or coding for interference-resistance possible with a more-complex digital radio, the SecurityMan's design leads to some compromise. The pure-analog approach wins out at the expense of radio robustness.

The basestation receiver antenna is an unbalanced dipole antenna (stripped coax, really), which feeds an apparent discrete RF front end. The basestation cycles through each channel selected, affecting changes to the RichWave RTC6503 frequency synthesizer with built-in VCO, whose output mixes with the received signal to get to the 480-MHz intermediate frequency (IF) used in the design.

After the mixer IF output is cleaned up in a surface acoustic wave (SAW) filter, audio and video signals must be further isolated. The former is addressed in an Atmel (Temic) U2860-B dual-channel FM sound demodulator, with only one of two channels needed for the SecurityMan's monaural output.

Baseband composite video is derived in a Zarlink-marked SL1461SA PLL FM demodulator, now seemingly an orphan part, given Zarlink's sale of its tuner and demodulator device business to Intel. Intel no longer lists the product as an active device in its demodulator family.

Outside of the A/V receiver circuits, the primary remaining base unit electronics are a 5-V regulator (LM7805) and another 8-bit microcontroller. Elan Microelectronics' EM78P153 MCU houses its own stash of about 7 kbits of one-time PROM. DIP-switch channel-select, reset, RF module control and blinky-light duties are all handled in this small, 14-pin device.

The electronic design relies on inexpensive, low-integration devices, and the CMOS sensor is arguably the most complex IC present.

I couldn't help but admire the cast-metal enclosures for the bullet cameras. These housings may represent the single most-expensive part of the total hardware bill of materials, surely under $50.

Despite the wireless descriptor, I was overwhelmed by the amount of wired stuff that came in the blister-packed setup. Three ac adapters–one for the base and one for each camera–made for quite a bowl of spaghetti, despite the reliance on RF links. If only we could handle power as conveniently and wire-free as the audio/video feeds seen in the SecurityMan/AEE design.

David Carey is president of Portelligent (www.teardown.com), a CMP company. The Austin, Texas, group produces teardown reports and related industry research on wireless, mobile and personal electronics.

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