amanpreetk
Junior Member level 2
How can I design an opamp circuit to amplify 2.5-3.5 volts voltage range to 0-5 volts, to be supplied to ADC of ATMEGA16? Which opamp should I use?
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Hi,
your input voltage range is 2.5 ... 3.5V, this makes a difference of 1V
Your output range is 0...5V, this makes a difference of 5V.
Gain = dUout/dUin = 5V/1V = 5
Now you can use a simple non inverting opamp circuit with gain = 5
Lets call the upper (feedback) resistor "RF" and the resistor to GND = "RG"
Now you need to compensate the input offset of 2.5V:
Here you may add a third resistor from -Vin to 5V (i hope this is your VCC). Lets call this pullup resistor = RU.
For gain calculations one must calculate as if RU is in parallel to RG
So the adjusted formula for RF is: RF = (gain -1) x 1/(1/RG + 1/RU) = 4 / (1/RG + 1/RU)
To achieve Vout =0V @ Vin = 2.5V the following formula must be true: RU = 1 / (1/RF + 1/RG)
combining both formula gives RF = RG * 3 / 2
Combining this in one of the above formula gives RU = RG = 0.6
Now i choose RG to be 20k0
then RU = 12k0
and RF = 30k0.
You need an RR output OPAMP, supplied with 0V and 5V.
Keep in mind, that even RR output opamps have a small dropout voltage to the rails.
Klaus
Hi,
try LMV321, or LMV358 (double), LMV324 (quad)
they should be cheap.
Klaus
Hi,
here schematic and simulation.
View attachment 109876
Blue = input
green = output
LMV358 is not in library, so i used another RR output OPAMP
Klaus
As i already mentioned:This is what I did..and my output does not reach exact 0 volts on input as 2.5v or 5 volts for 3.5v as input
Keep in mind, that even RR output opamps have a small dropout voltage to the rails.
Thats a simulation problem, not in reality.And moreover if i don't apply 1k ohm resistor with the input voltage, the proteus gives error as
Typical offset voltage is about half the amount shown in the simulation, but maximum value is higher. In so far it's a realistic result. Expecting no offsets means ignoring real component behaviour.So i expect better quality than the simulation shows. It should work fine.