The VGA Test Box Circuit


Posted on Feb 7, 2014

There are actually very few electronic components necessary for this project as the PIC Microcontroller is the powerhouse doing most the work. The few components necessary like, buttons, switches & power circuit are trivial forms of I/O which makes understanding how the project works eveneasier. The power circuit is just a 9v Battery hooked up to the LM7805 with a


The VGA Test Box Circuit
Click here to download the full size of the above Circuit.

1uF capacitor hooked to output & ground of the LM7805 to keep a steady 5v DC. The SPST buttons are tied to ground so when the button is pushed the I/O pin it is attached to is effectively tied to ground. To avoid having a short circuit when the button is pushed, 4. 7K © or 10K © pull-up resistors are used. The SPTT Switch is a non-standard 3 way switch. It can be substituted with any other type of button(s) or switch(es) that will allow 1 input to go to one of 3 outputs. It is optional but you can just tie the wire directly from the PIC to one of the the CRT R/G/B inputs. It`s just a matter of which color will display, Red, Green or Blue. This is tied high (logic 1; +5v) once again using a pull-up resistor. Pin 1 is effectively a reset pin. The PIC will restart-Memory Clear-when this pin is low (logic 0, +0v). For this project I did not include a reset button so I just have the pin tied high always, so the PIC will always be running as long as it is powered.




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