I read the document http://instruct1.cit.cornell.edu... on how generate TV images (on NTSC TVs) using a 2-bit DAC controlled by the ATMEGA644. Please see the attached image of the schematic of the 2-bit DAC.
Basically, it's a resistive voltage divder to calculate out the voltage for white and black levels, depending on the output voltages from pinD.5 and pinD.6
We operate at 5V. I know not exactly 5V output from pins, more like 4.75V something, but, let's just use 5V.
Here is my calculations. Are they correct? And what would be Vout for item (4), when pinD.5 and pinD.6 both output 5V? Thanks!
1. pinD.5 = 0V and pinD.6 = 0V
Vout = 0
2. pinD.5 = 5V and pinD.6 = 0V
Vout = (75ohm/(300ohm + 75ohm)) x 5V = 1.0V WHITE LEVEL
3. pinD.5 = 0V and pinD.6 = 5V
Vout = (75ohm/(1000ohm + 75ohm)) x 5V = 0.35V BLACK LEVEL
4. pinD.5 = 5V and pinD.6 = 5V
Vout = ???