Miniature Black and White TV System


Introduction:
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:

  • Miniature black and white video camera, 12VDC, Model PC-206XP
  • Video modulator block, Jameco 141639CJ or equivalent
  • Sony Watchman miniature TV
  • 12V DC power supply, beware of wall-warts – they often have inaccurate voltage ratings.
  • Miscellaneous wires and cables

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