[SOLVED] Op amp to rescale A/D input

[fendertunes]

I have a 0-5V sensor output that goes to an op amp buffer and then to an A/D. I only need data from 1-3.3V from the sensor output. Chopping the top end is easy by using a zener clamp or something similar. How do I remove the bottom end, so I don't see 0-1V data. I figure use an op amp, but what configuration?

 

[enjunear]

If the output of your A/D is an device running software/firmware, why not just do your value-limiting in the code?

pseudo-code:
value = read_adc()*5.0/1023; (assumes 10-bit ADC, gives you value from 0 to 5)
if value >= 3.3 then value = 3.3;
if value <= 1.0 then value = 1.0;

 

[E-goe]

What about adding an offset circuit to shift the lower range and apply gain to clip to upper range?

E-goe

 

[fendertunes]

enjunear, the sensor output gets buffered and goes into a 0-3.3v a/d.

E-goe, I was thinking about that (offset and clip the upper part). So, if I do 1V offset (to remove the lower range), then the output of the opamp will be 1V when no input is applied? Because of the dc bias. What I want is, between 0-1v sensor output, the oamp sits at 0V, and from 1-4V, the output of amp is 0-3V.

 

[0by1]

@fendertunes:
I was thinking about that (offset and clip the upper part). So, if I do 1V offset (to remove the lower range)

why do you want to loose sensor data?
why do you want 1v offset at o/p?

you can do this using summer circuit and ref. voltage to scale sensor data to ADC i/p data.

 

[fendertunes]

Because I know where my sensor reading will be for the most part, so I don't want the whole range... I want to extract just the data I need, maybe put some gain on it, and send it to A/D to look for small changes.

I am using a single supply op-amp, so summing can work. Though I want it such that I don't have a 1V output with no input. It's almost as if I want on the order of two schottky drop... but that won't give me the precision, so I don't want to use that.