VGA Blinking Lights

This project consists of a a device capable of generating a (pseudo) random blinking lights pattern. The objective of this project is to turn old monitors, specially CRTs, into decorative objects. The VGA video generation is performed by the PIC counting cycle by cycle. At 20MHz the PIC executes one instruction cycle at each 200ns. It means that a whole VGA line (31,77us) shall last 159 cycles. This value is rounded up but close enough for a stable image (full detail) The VGA output is impedance and amplitude controlled. It can be achieved by doing some math. The values are not critical, though. Anything about 20% of the calculated values are good enough. The randomness is generated by using a Galois LFSR (Linear Feedback Shift Register) with a different seed for each line of 8 ‘dots’. The code was borrowed from PICLIST. The timing for colour changing is done counting frames on the last blank line of a screen. The interval time is formed by adding 22 with the 4 least significant bits of one of the random variables used to control the colour of the dots. This results in a time of .36 to .63 seconds for each change. And that’s all.”

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