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#1
09-23-2009, 07:11 PM
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Circuit using optocoupler for feeding baseband video to hot chassis TV monitor
Here's an old circuit I did years ago to inject baseband video into a hot chassis solid state TV set. About 10MHz bandwidth thru this optocoupler. You can still get the optocoupler from DigiKey. The output of this circuit would substitute for the video that would come from the set's video IF demodulator circuit (though you may need a gain stage to boost the amplitude to what the demod circuit generated).
To power the cold side of the optocoupler circuit, wrap several turns of wire with thick insulation around the core of the flyback transformer, keeping these turns away from the very high voltage winding and other windings for that matter. Then use a high speed rectifier diode (like from a switching power supply secondary rectifier) and some filter capacitor to create the 12VDC. You will see different voltage output depending on which way the diode is connected (it's an asymmetrical waveform unlike the usual powerline sinewave, it looks somewhat like a square wave of about 10% duty cycle). And add or remove turns to get close to the 12VDC. This is a project only suitable for an advanced electronics hobbyist, not for newbies. You'd need experience in building 10MHz wide band analog circuits to have success. Just wanted to give fair warning what you'd be in for...
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#2
09-23-2009, 08:15 PM
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Cool, I'm not a pro but might try it anyways. Seems pretty straightforward. Maybe on some rainy day after all the roundies are workin'.
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