[Help] LM324 Cricuit

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jjeevan007

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hi to all,

if anyone could explain the following circuit operation then it would be very much help full..........
 

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Hi;
Where is vout- and vout+ connected? There are opamps in this device but adc_in4 and vout- is directly connected to opamp negative and positive inputs.
In this case isn't it force to make adc_in4 ~= vout-?
May be i am wrong, not sure, but i think something is missing in the schematic.
 

At first sight this is seems a non-standard config of opamps.

Main issue is -- the + inputs of the 2 opamps are designated as OUT- and OUT+. Without knowing what this is conencted to it is almost impossible to work out what this circuit does.

I think it could be a 2-opamp differential amp config... where OUT- and OUT+ are actually inputs from the sensor. In that case it is a standard config, except for the 220 ohm resistor, and also the point at which the ADC_IN value is taken from.
 


vout- and vout+ are connected to output of a sensor (load Cell)

and adc_in4 is connected to ADC input...........

- - - Updated - - -


i also think its differential amp, but i know want what is the gain if its differential amp..........
 

jjeevan007 said:
i also think its differential amp, but i know want what is the gain if its differential amp..........
Click to expand...

without doing the analysis, and using spice to simulate it, I get a gain of exactly x100 at the pin 14 (2nd opamp output), and a gain of ~3.8 at the point you have connected the ADC.

The 220 ohm bumps up the gain from the standard differential config to provide (10K/ 1K) x (1 + 2x 1K / 220).
 

please can u tell me, why we are using 10k pot........

and wt should be the valve of it................
 

10K pot is used for setting the center or average value of the output. You can think of it as a DC offset so that your output is always positive.

If you are feeding pin 14 to an ADC input, then I suggest that you set this pot so that voltage at the center tap is 2.5v. Then with a gain of x100, and a maximum swing of 1v - 4v for the opamp (assuming you are powering from +5v, and using lm324 which is not rail-rail), then the maximum input should be <= (4-1)/100 = 30mV pk-pk.
 

i got the your answer but above circuit is not amplifying correct, it is giving the constant voltage of the 10k pot......
 

jjeevan007 said:
i got the your answer but above circuit is not amplifying correct, it is giving the constant voltage of the 10k pot......
Click to expand...

It is a differential amplifier. It amplifies the differential voltage between OUT+ and OUT- only. Any common-mode signal is not amplified. Where are you applying your input signal ?
 

same out+ and out- only..........

out+ is around 2.5611

out- is around 2.5620

i am getting a fixed voltage around 2.5
 

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