[SOLVED] Op amp to rescale A/D input

Status
Not open for further replies.
F

fendertunes

Junior Member level 1
Joined
Apr 26, 2011
Messages
16
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,402
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?
 

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;
 

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

E-goe
 

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.
 

@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.
 

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.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…