Composite video to vga converter schematic

The advantage is that a raster will be present in the absence of a video signal so one does not have to worry about all the precautions with the oscilloscope before and after using the converter. More importantly, a loop is introduced in the circuit from the output to the trigger input to allow the 555 timers to operate in astable (free running) mode. Version 2: Improved Solid-State ConverterДЄmong the improvements on version 1 includes the use of the 2N3906 and associated resistors for improved linearity of the sawtooth output. I don't have any pictures of the converter because I built it on a breadboard and disassembled it soon after some screenshots were taken.ДЄ view of my workbench (notice the soldering iron and the plugs) More information on the theory of how the circuit works or tricks with video can be found on the VGA-to-Scope converter page. This converter is not as robust as the VGA-to-Scope converter so every time the circuit is powered up, the oscillators probably need readjustingso consider the 1Meg pots to be vertical and horizontal hold controls. The same goes for shutting down, turn down the brightness of the oscilloscope before you shut down the video source and/or converter. Make sure you have a raster before you turn up the brightness. Without the video signal connected, the sweep generators are not operating due to the absence of sync signals so a dot appears on the CRT, which can burn the phosphor. Second, the video MUST be connected before you turn up the brightness of the oscilloscope.

This circuit includes another 555 to generate the negative supply rail for the op-amps.Д¬AUTION: The oscilloscope must have a X, Y, and Z axis, good gain, and X/Y inverters for this converter to be useful. If an inverter is preferred to make the video 'positive' then here is a schematic for the inverter below as taken from the VGA-Scope converter. I didn't really mind since this circuit took only 10-15 minutes to slap together. The intensity signal comes from the composite video signal itself, but is negative. The chip provides the vertical sync on pin 3 for the vertical oscillator, and composite sync on pin 1 for the horizontal oscillator. Below is the schematic.ДЄ LM1881 is used to do all the grunt work of separating the sync signals from the composite video. When the pot is set just right, the capacitor will charge up at the correct rate and the trigger signal causes the 555 to discharge the capacitor for synchronization. The continuous current supply to charge up the capacitor linearly (the 3906 PNP transistor and associated resistors) was replaced with a simple 1Meg pot from 5V to charge up the capacitor, albeit creating a nonlinear sawtooth. The circuitry in the VGA-to-Scope converter has been greatly simplified op-amp buffers and inverters were eliminated. This project takes after the VGA-to-Scope converter by using composite video rather than VGA signals to create a display on an oscilloscope.

Composite video to vga converter schematic