Category: Main page » RF Circuits

Miniature Black and White TV System

(C) G. Forrest Cook 2005


Mini camera (in vise jaws), modulator and Sony Watchman


Close-up photo of miniature B&W camera

INTRODUCTION

August 30, 2005

Incredibly small video cameras have recently become available at reasonable prices. Small televisions are available for very little money at online auction sites such as eBay. It is now possible to build a miniature short-range wireless video system with off-the-shelf parts. This wireless nature of this circuit is not suitable for long distance operation, the video modulator just provides a simple method for interfacing the video signal to a standard TV. Transmission distance is limited to a few feet.

Theory

The 12VDC supply provides power for the camera and video modulator circuits. The video from the camera is fed into the video input of the modulator circuit. The modulated RF from the modulator is fed into a small antenna. Use of a dipole antenna that is resonant at the frequency of the modulator can extend the signal range. The RF travels across a short distance to the Sony Watchman TV receiver. A black and white image magically appears on the TV screen.

Construction

The camera's video signal is connected to the video modulator with an RCA jumper cable. Power to the camera and video modulator is connected to the 12V power supply. Be careful with polarity, reversing the leads may damage the modulator. The camera that was used had reverse polarity protection built in. The modulator's RF output signal is connected to a small antenna, the antenna can be made with two short lengths of #16 gauge solid wire. Alternately, for long distance wired operation, the RF signal can be fed into a length of 75 ohm coax cable with a 75 ohm terminating resistor across the far end of the cable. Connect the remote center conductor of the cable to the TV antenna through a 330 ohm resistor.

Use

Turn the power for the camera and modulator on, turn on the TV. Tune the TV to the channel of the RF modulator, fine-tune the TV for the best picture. For full-time operation, use the appropriate AC adapter for the watchman. If battery operation is desired, run the TV from its internal batteries and use a 12V battery for powering the camera and modulator. A rechargeable lead acid battery with a series fuse (and a recharging circuit) is recommended.

A fun use for this system would be to create an engineer's view of a model train layout. A loop of wire near the track would make a good receiving antenna. Power could be pulled from the engine motor circuit using a bridge rectifier feeding into an electrolytic capacitor, just make sure not to exceed the camera's 12V maximum supply voltage.

Parts

Source:www.solorb.com


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