display positive and negative side of a waveform

Projects General Guidance
1

I am trying to display 4 sensors outputs on serial plotter out of which one is sinusoidal signal from function generator. But I am able to display only positive side of the waveform for all inputs. Please help me to modify my code given below so that I can also display negative side:

void setup() {

Serial. begin(9600);
}
void loop() {
int svalue1 = analogRead(A0);
int svalue2 = analogRead(A2);
int svalue3 = analogRead(A3);
int fvalue = analogRead(A1);
Serial.print(svalue1);
Serial.print(",");
Serial.print(svalue2);
Serial.print(",");
Serial.print(svalue3);
Serial.print(",");
Serial.print(" ");
Serial.println(fvalue);
delay(200);
}

2

The Arduino ADC will only read positive values so the waveform must be biased, before conversion, so that it will always be positive only. Subtract the value of the bias voltage from each reading to get the actual voltage before the bias is applied.

Edit: There is a very real risk of damaging the Arduino if you apply voltages more negative than -0.5V to an analog pin.

3

Might also be able to use a opamp to “split” the signal between 2 pins so that one pin receives top half of the wave as your currently doing, and the other pin receives a inverted version of the bottom half.