Here is a simple TV transmitter. The circuit is simple and really quite crude, but it does include MONO sound. I have not shown the two regulators in the drawing. These are one 12v DC 1A series regulator chip, and one 8v DC 1A series regulator. I fed the 8v regulator from the output of the 12v regulator. The rest of the circuit looks like figure above.source

This is an 8-input x-output audio/video switch module to be controlled from a computer, for example from the parallel port. Each audio/video output can be switched to any of the 8 inputs, separately. One module drives one audio/video output and has a 34-pin connector to plug into the system interface.You can use video OPA-s on the 4051 output instead. source

The simplest black level clamp consists of a signal diode (1N4148) reverse-biased to ground from the output line of the input buffer above and a 4k7 resistor in parallel with it. That forces the sync tips to be at (gnd - threshold voltage of the diode), which shifts the black level of a 2x amplified video reasonably close to ground. Add that and you can connect the two circuits  together and see how they work. They should be very good as far as the signal quality goes (maybe not broadcast quality, but no visible signal degradation). Don’t forget good power supply bypassing, use at least 220u of electrolytics and 100n ceramic caps near the transistors on both circuitssource

The design is based on a switchable array of six Maxim MAX4258 dual-channel video multiplexer-amplifiers.Gain-change settling time is lower than 30 nsec. The greater-than-100-MHz bandwidth of each stage results in an overall passband for all gain settings of greater than 60 MHz. The five lowpass-bandpass capacitors, C1 through C5, determine the lower end of the passband.source

The circuit needs that the VGA card sends out the video signal the the RGB format compatible with PAL or NTSC standard video timings. This is accomplished with right VGA to TV driver.This circuit is based on AD722 IC from Analog Devices. The AD722 is a low cost RGB to NTSC/PAL Encoder that converts red, green and blue color component signals into their corresponding luminance (baseband amplitude) and chrominance (subcarrier amplitude and phase) signals in accordance with either NTSC or PAL standards. These two outputs are also combined to provide composite video output. All the outputs can drive standard 75 ohm terminated video cables directly without extra amplifiers. The chip is a very compact solution, because operates from a single +5 V supply and it need no external delay lines or filters.

• Power supply: Regulated +5V power supply, needs less than 300 mA
• Video input: R G B + HSYNC + VSYNC from VGA card, refresh rate compatible to PAL or NTSC standards
• Video outputs: Composite video and S-video (Y/C)
• Video standards supported: PAL B,G,H and NTSC M

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