[sdiy] CV offset question.

[Dave Kendall]

Thanks Paul.

In fact, as I will always only need a negative offset, I guess I can get
away with just a 7905, so ends of pot = -5 and GND. (I'm guessing that GND
is the same as the point exactly halfway between -15V and + 15V, and that
there won't be a problem with this - it would reduce the swing further,
making the pot's travel cover an even smaller voltage range).
Paul Perry suggests 2 resistors in series with the wires to the ends of the
pot. It should be worth a try first before going for the LT1013CN8. (which
does look rather good from what I can tell from the datasheet....)


cheers,

Dave 



> 
> Use 2 regulators a 7805 and a 7905 to reduce the 'swing' by a factor of 3.
> Then, 
> use a LT1013CN8 from www.digikey.com. This is a special op amp that is
> *specifically made* for very accurate scaling/summing of DC voltages. OK, it's
> $4, what's your point? :)
> 
> Lastly, you can't 'add in' the voltage off the pot wiper directly, you need to
> use an op amp summer that lets you use the ratio of 2 resistors to then take
> the 
> +-3V swing to whatever you need.
> 
> Paul S.
>