I'm going to try and generate black and white NTSC video, using
a micro-controller. According to this: It is possible to do it
using two pins of Atmel Mega644. I looked at the datasheet and
noted that the IO is 1.8 V. For NTSC you just need three
voltages sent at the correct time, 0V, 0.3V, and 1V. What I
don't understand is how does this circuit generate the 0, .3 and
1V. When I do the calculations it doesn't really add up. I
simulated this using TI TINA simulator, 2 batteries and switches
inplace of the IO ports, and trying all four combinations of the
IO, I can get 0, .3V but not 1V. Can someone using math explain
how you can get 0 V, .3 V, and 1 V using the circuit shown in
the link above. I also, I guess what I don't understand is the
uC IO equivalent circuit for simulating in a SPICE program, is
it just a battery set to the IO voltage? Or maybe an OP AMP with
the output set to the IO voltage can someone please explain
this. Any help is appreciated.