High(4.7V) Voltage in an Analog Input

Forum 2005-2010 (read only) Hardware Troubleshooting
1

Hi fellows Im new in this Arduino world and I had a extrange behaviour today, I was using the Analog Input 0 for get the output of a Sharp distance sensor and all was ok, but now the Input is not working and I tested with a multimeter and the input measures a 4.7Volts, anyone have had this problem in the past?

2

Have you accidentally configured the pin as a digital output?

3

If you disconnect the signal wire from analog pin 0 and then measure the sensor wire, what voltage do you read? If it's still +4.7 then it would point to a sensor problem, no?

Lefty

4

Have you tried connecting the sensor to other analog pins? Perhaps you have blown the A0 pin? What voltage does the sensor use?

5

Try put a pull-down resistor between the analog input and the ground (anything between 100k and 1M should do the trick) and measure with multimeter again. I am wondering if there's some kind of interference.

If the problem goes away, you might want to leave the resistor there.

6

Thank fellows for reply so soon,

The sensor uses 5V but Im feeding it with an external Power source.

I conected the sensor to the Analog 1 and all is ok, even if I read the A0 pin with no conection the output is 1023, I will try with the resistor and I will tell you,

this is the code I am using:

void setup() {
  Serial.begin(57600); //57600
 }
 
 void loop() {
  // read the analog input into a variable:
   int analogValue=0;
   delay(5);   
   analogValue = analogRead(0);
   Serial.println(analogValue);   
   delay(5); // print the result:
   // wait 10 milliseconds for the analog-to-digital converter
   // to settle after the last reading:   
 }
7

Are ypu ABSOLUTELY sure that the grounds of the two supplies have stayed connected ? If they are disconnected for even a short while with power on, you have a VERY good chance of blowing the input.