analogRead() inside a loop always returns 0

Question

I wrote Arduino code to receive analog input from different voltage dividers connected to four pins (A0 to A4) and analog input from a temperature sensor (LM35) to A5. analogRead inside the for loop always returns zero whereas analogRead outside the for loop returns correct values.

What has to be changed to get correct values?

int time=0,y=0;
float volt;
String str;
int countParallel=0;
float voltage[]={0,0,0,0};
float temperature=0;
int sensors_pin[]={A1,A2,A3,A4,A5};
String x="";
// the setup rouontine runs once when you press reset;
void setup() {
 pinMode(2,OUTPUT);
 pinMode(3,OUTPUT);
 pinMode(4,OUTPUT);
 pinMode(5,OUTPUT);
 pinMode(6,OUTPUT);
 pinMode(7,OUTPUT);
 Serial.begin(9600);
 Serial.setTimeout(50);
}
// the loop routine runs over and over again forever;
void loop() {
 Serial.println(analogRead(A5)*500/1023);
 delay(1000);
 while (Serial.available() > 0) {
 int inChar = Serial.read();
 if (isDigit(inChar)) {
 x += (char)inChar;
 }
 }
 // Parallel Disharging
 // Serial.println(x);
 if(x.toInt()==1) {
 digitalWrite(13,HIGH);
 if(countParallel<1) {
 digitalWrite(6, HIGH);
 digitalWrite(7, HIGH);
 countParallel++;
 }
 for(int i=1,x=14;i<=5;i++,x++) {
 if(i<4) {
 Serial.println(analogRead(x)*(5/1023));
 delay(100);
 } else if(i==5) {
 Serial.println(analogRead(x) * p(500/1023));
 delay(100);
 }
 if(volt<2.8){
 digitalWrite(i+1,HIGH);
 } else if(temperature>40) {
 digitalWrite(2,HIGH);
 digitalWrite(3,HIGH);
 digitalWrite(4,HIGH);
 digitalWrite(5,HIGH);
 }
 }
}
// Series Discharge
if(x.toInt()==2){
 for(int i=A0;i<=A4;i++){
 if(i<A4) {
 voltage[i] = analogRead(sensors_pin[i]) * (5/1023);
 Serial.println(10);
 delay(100);
 } else if(i==A4) {
 temperature = analogRead(sensors_pin[i])*(500/1023);
 Serial.println(9);
 delay(100);
 }
 if(volt<2.8) {
 digitalWrite(i, HIGH);
 delay(100);
 } else if(temperature>40) {
 digitalWrite(2,HIGH);
 digitalWrite(3,HIGH);
 digitalWrite(4,HIGH);
 digitalWrite(5,HIGH);
 }
 }
 }
} 

Answer 1

voltage[i]=analogRead(sensors_pin[i])*(5/1023)

Is equivalent to

voltage[i]= analogRead(sensors_pin[i])*0
 = 0;

You are using an integer division, not a floating point divsion. 5 / 1023 evaluates to 0, 5.0f / 1023 evalues to 0.00488... You have repeated this error throughout your lower loop code, which is why you're only getting 0.

In your outer loop you printed it as

Serial.println(analogRead(A5)*500/1023);

Which will first multiply by 500, then divide by 1023, which works. But since you put the above expression in parenthesis, it was first evaluated.

• Edgar Bonet: As a side note, it's 1024 rather than 1023.