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Video Wire: Enable Video Transmission Via Long Cables

2016-09-13 03:58  
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This circuit enables you to connect your camera with very long wire. The circuit is actually a video amplifiers. At the sender part, the amplifier is used to make a stronger signal. This stronger video signal then can be transmitted through the long cables. The signal is transmitted using balanced mode, where two wires are driven in the opposite phase. Here is the schematic diagram of the circuit:


video wire circuit circuit schematic

The resistance of a typical four conductor flat 28 gauge telephone wire is about 7 ohms per 100 feet. Since voltage drops appear in both the plus and minus power supply leads, the total series resistance is about 14 ohms per 100 feet. Maximum allowable wire length depends on the total current requirements of the camera and send board. Using a camera that draws 100 ma, for example, a total current of about? 180 ma is required and therefore a maximum of approximately 500 feet of 28 gauge flat telephone wire can be used. If a longer wire is needed, the round type of 22 gauge four conductor telephone wire offers much lower resistance. Its resistance per 100 feet is approximately 3.3 ohms total for both the positive and negative power wires. Using this wire and a 100 ma camera, the wire length can be approximately 2000 feet.


D1 – 12 volt 1 watt zener diodeD2 – Motorola MVAM109 tuning diodeD3 – 10 volt 1 watt zener diodeBR1 – 1 amp 400 volt DIP bridge rectifierC1 – 22 mfd 6.3 volt tantalumC2, C3, C4, C9, C10, C11, C12 – 1 mfd 16 volt tantalumC5 – 3.3 mfd 16 volt tantalumC6, C7 – 22 mfd 16 volt tantalumC8 – .1 mfd 50 volt metalized filmC13 – 2200 mfd 50 volt electrolyticC14 – 1 mfd 50 volt tantalumR1, R15 – 75 ohms 1/8 wattR2, R9, R10 – 10K 1/8 wattR3 – 200 ohms 1/8 wattR4, R14 – 4.7K 1/8 wattR5, R6 – 51 ohms 1/8 wattR7 – 330 ohms 1/8 wattR8, R11, R13 – 100 ohms 1/8 wattR12 – 200 ohms potentiometerR16 – 160 ohms 1/4 wattR17 – 100K 1/8 wattR18 – 10K potentiometerR19 – 15K 1/8 wattR20 – 8.2 ohm 1/2 wattR21 – 150 ohm 1/8 wattR22 – 100 ohm potentiometerR dummy – 100 ohm 2 wattJ1 – RJ11 6P4C telephone jack with leadsJ2 – RJ11 6P4C board mount telephone jackJ3 – chassis mount angle coaxial F connectorIC1 – Maxim MAX435 dual output amplifierIC2, IC3, IC5, IC6 – 78L05 voltage regulatorIC4 – Maxim MAX436 single output amplifierIC7 – LM317  adjustable voltage regulatorT1 – 24 volt AC 400 ma adapter transformereight 6-32 X 1/4 inch screwsrubber grommet for 1/4 inch hole2.2 X 3.3 X 4 inch metal enclosure with vent holesfour conductor telephone wire with RJ11 plugsTO220 5 watt clip on heat sinkfour threaded spacers 6-32 X 1/2 inch long


The core of this circuit is the MAX435 transconductance? amplifier. Their wide bandwidth feature is suitable for video signal application. The balanced mode used in this video wire circuit make sure that any noise exsposing the cables would cancel each other at the receiver. [Schematic diagram source: aeiproducts.com]

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