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.