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Schmitt Trigger vs. Rails vs. Mark/Space Ratio

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Hello,

I'm using a classic 2x transistor Schmitt Trigger design powered by +/12V rails.

If there was any minor changes in the output voltage of the plus or minus rails - e.g. between different OEM power supplies, or if the rails were operating at e.g +11.75 and -11.50 rather than exactly +/-12V...

...under normal use - would this factor by itself have any effect on the mark/space ratio between the high and low period?

I'm guessing not - but I was curious enough about to want to ask!

Thanks,

/ J
 

I'm going to make some assumptions... since you refer to Mark & Space, this is serial communications. From the nominal +/- 12 I'd guess it's 232? The thresholds for 232 are +/- 3V, so you could have very different voltages for the + & - rails and it would still work, just maybe not a some distance\speed combinations. Newer 232 chipsets (notably Maxim, but most others as well) don't even look at the -3 anymore but see an idle state at below +1.5, so they are doing more to shift any "symmetry" than you are. You are correct that it will not have any affect when it comes to decoding the signal.
 

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