A Low Cost CCTV System (ET/D, July 1981)

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A front door monitor--and much more!

Closed circuit TV is becoming a consumer product. It is valuable for security purposes, monitoring the front door, the swimming pool, the nursery, anywhere that needs remote watching. Here is ET/D's impression of one of the more inexpensive systems.

Fig. 1. The GBC Look-Out 2000 system, camera, monitor, and intercom speaker.

by Walter H. Schwartz

When ET/D first received product announcements on GBC's Look-Out 2000 CCTV system we were mildly surprised to see a system aimed at the residential market. We asked to be allowed to evaluate one and have found the Look-Out 2000 to be very functional and useful.

The Look-Out 2000 consists of a small CCTV camera and a modified black and white 12 inch television receiver and an intercom speaker signal unit which, in effect, can replace a doorbell. The camera is positioned where it can view anyone who rings the doorbell (weatherproof housings are available) and the speaker unit is mounted where one might position the doorbell button. The monitor is positioned in the kitchen, bedroom, or wherever one wishes to monitor from. The monitor can be used as a conventional receiver; when the intercom button is pushed it switches automatically to monitor, or it can function a monitor continuously.

We used the Look-Out 2000 in a typical sort of installation (your editor's home) and monitored the front door from the workshop and study which are in the back in the basement. It's great! No more running upstairs and through the house to answer the door; just tell the kids that ring the doorbell that there is no one home, from downstairs!

Fig. 2. Schematic of the GBC Look-Out 2000 CC7V camera.

Fig. 3. A camera weatherproof housing.

Fig. 4. The GBC Look-Out 2000 camera internal view. This model differs slightly from the schematic.

The system works very well. It is stable; it uses a crystal controlled sync generator. It has adequate contrast under almost all lighting conditions; room lights or the front door light are quite sufficient lighting.

The camera is straightforward in design and construction (See Figure 2) as the schematic diagram would indicate. IC's are used extensively for much of the video gain, as the sync generator, as the horizontal and vertical pulse formers, vertical output stage, voltage regulator, and a transistor array IC. IC-101, is used as sync amplifier, blanker, clamper, and two stages of video amplification and an IC is used as a temperature control sensor amplifier (in some models). Considerable design effort has apparently been made to make the camera as automatic, as adjustment free as possible. There are no external adjustments other than the mechanical focus of the lens. Vidicon adjustments are internal setup adjustments. Adjustment for changes in ambient light are made by automatically adjusting the target voltage (see Figure 2). Video from pin 8 of IC100 is rectified by D100-D101 and its average level sets the collector voltage of Q100, the ATC (Automatic Target Control) amplifier and thereby the vidicon target voltage.

Most of the camera circuitry is so similar to receiver video and sweep circuitry it needs little explanation.

Sync is developed from a 31.5KHz oscillator driving pulse countdown and shaping ICs. The horizontal sweep and the high voltage use separate driver and output transistors, both systems driven by IC105. The various G2, 5, 3, 6 and focus and target voltages are derived from this scan frequency source. There are no great mysteries here.

Video from the target of the vidicon sees a very high impedance load presented by Q101, a source follower. Q102 and IC-100 are simple video amplifiers. IC101 is a transistor array as mentioned earlier, within it, transistors IC101E and IC101C are differential amplifiers which drive Q102 an emitter follower which can drive a considerable length of coaxial cable to a monitor. Sync is added via D111 and sync amplifier IC101A, horizontal via D106, and vertical via D107.

Now for a little editorial comment.

These inexpensive CCTV systems have broad application. The front door watch is only one of the most obvious.

They can watch a swimming pool, small children playing in a back yard, your prize tomato plants if you are afraid of vandalism, a farmer's prize sow about to give birth, the aisles in your store (or the cash register if you don't trust your clerk), and the price should make the equipment saleable.

This GBC system has a suggested list price of just a little over $400, with a reasonable dealer profit. With immediately available optional equipment up to three cameras can be switched to one monitor. Wide angle and telephoto lenses are available as are mounting brackets and weatherproof housings. And you should be able to both sell and service it; it should fit your business well.

(source: Electronic Technician/Dealer)

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