In SX Microcontrollers, SX/B Compiler and SX-Key Tool, peterverkaik wrote:

I did some calculation on the following schematic to see if
video level signals could be generated with one pin.

+5V o--[ R1 ]----+
pin o--[ R2 ]----+  level
                 |
               [ 75 ]
                 |
                 V

pin   signal   level
 L    sync     Vs
 I    black    Vb = 0.3 + Vs
 H    white    Vw = 1.0 + Vs

white:
     75
------------- * 5 = 1.0 + Vs
75 + (R1//R2)

black:
  75
------- * 5 = 0.3 + Vs
75 + R1

sync:
   (75//R2)
------------- * 5 = Vs
(75//R2) + R1

If you work this out, the results are (exactly !):
R1 = 175 ohm
R2 = 210 ohm
Vs = 1.2V
Vb = 1.5V
Vw = 2.2V

Has anyone tried this, and does the 1.2V dc offset bother the video input
(I believe not because these are mostly ac coupled).

regards peter

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