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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.
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.
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).
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.
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 ?
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