Hello everyone,
So here is my problem..
I made this VGA interface from my FPGA to my monitor .It worked great, but i was not quite satisfied with the 8-bit color (256 colors) i was limited to.
So a wild idea came to my mind, why don't i use the pmod (i/o general purpose pins) on my Digilent Nexys 3 FPGA as output pins, and make a little DAC on a breadboard an have like 12-bit colors or more.
I must admit i'm no expert in electronics(this is my first circuit actually), but this idea got me excited and i bought a multimeter, a lot of resistors, wires and a breadboard to make a resistor ladder to divide my voltage.
Everything was fine until i realised that the IO pins(which i can set to '0' or '1' 0v or 3.3v) have a dark secret .An IO pin set to '1' is not the same as the VCC pin (see image bellow).They both should be 3.3v and they are if i measure them separetly with my multimeter, but when in the ladder the VCC pins work great, while the IO pins set to logic '1' (3.3v) go down to 2.9, 3.1 or other values.
I suspect that they somewhat interract with eachother and the ladder makes them go that way...
But i'm kind of lost and i really need your help !
I will attach a picture of the ladder schematic bellow.
Thank you !