Technical problem (OT)

From: MikeS <*dm561_at_torfree.net*> Date: Sat, 25 Sep 2010 16:54:21 -0400 Message-ID: <27053533300E44EEABF85D8D7F1D4ED5@vl420mt> · dm561_at_torfree.net

> Subject: Re: Technical problem (OT)
> Hallo allemaal,   For those who already answered: thank you very
> much! Your
> answers  showed that I am not becoming senile and that you have
> troubles
> with the schematic as well :)  Let me ask one straight question:
> where is
> the common ground ???   --     ___    / __|__   / /  |_/
> Groetjes, Ruud
-------------
There is no "common" ground as such; the effect of the LED and resistor 
connected to -12V (TXD) will be to offset the TI's ground approximately -2V 
(the LED's forward drop) with respect to the PC's ground and convert a 
unipolar signal to a bipolar one.

Assuming a voltage swing on the TI's data lines of +5/0V the PC would see 
approximately +2/-2V on the data lines.

At least that's what it looks like to me...

mike 

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