(solved) Newbie Question : Do I have a dodgy board?

Development Tools IDE 1.x
1

Hiya... just working my way through various tutorials... and am beginning to suspect that all is not well with this arduino (duemilanove ATmega 168).

So I wrote a little programme to test input on every pin...

/*

  • Switch test program
    */

int s1 = 1;
int s2 = 2;
int s3 = 3;
int s4 = 4;
int s5 = 5;
int s6 = 6;
int s7 = 7;
int s8 = 8;
int s9 = 9;
int s10 = 10;
int s11 = 11;
int s12 = 12;
int s13 = 13;

void setup() // run once, when the sketch starts
{
Serial.begin(9600); // set up Serial library at 9600 bps
pinMode(s1, INPUT);
pinMode(s2, INPUT);
pinMode(s3, INPUT);
pinMode(s4, INPUT);
pinMode(s5, INPUT);
pinMode(s6, INPUT);
pinMode(s7, INPUT);
pinMode(s8, INPUT);
pinMode(s9, INPUT);
pinMode(s10, INPUT);
pinMode(s11, INPUT);
pinMode(s12, INPUT);
pinMode(s13, INPUT);
}

void loop() // run over and over again
{
Serial.print(digitalRead(s1));
Serial.print(digitalRead(s2));
Serial.print(digitalRead(s3));
Serial.print(digitalRead(s4));
Serial.print(digitalRead(s5));
Serial.print(digitalRead(s6));
Serial.print(digitalRead(s7));
Serial.print(digitalRead(s8));
Serial.print(digitalRead(s9));
Serial.print(digitalRead(s10));
Serial.print(digitalRead(s11));
Serial.print(digitalRead(s12));
Serial.print(digitalRead(s13));

Serial.println("");
delay(100);
}

And when I upload it - with absolutely nothing connected to the board, it outputs this:

1110000000000

1110000000000

1110000000000

1110000000000

1110000000000

1110000000000

1110000000000

1110000000000

1110000000000

1110000000000

Which makes it look as though the first 3 pins are permanently receiving "1"

Is that what it's supposed to do?

It also does this thing where if I set any of the 0 pins above to high, not only does that pin go to 1, but several of the neighbouring ones do as well.

Any help most appreciated

Nick

2

First point is that serial communications with the PC uses pins 0 and 1, so you shouldn't be setting pin 1 to input mode as it's the transmit pin to the usb serial link. So don't use pins 0 and 1 until you gain more experiance and understand the trade-offs of when you can and cannot use those pins.

Second, you should be aware of what are called 'floating input pins'. When there is nothing wired to a digital input pin it has no valid logic voltage reference and is just responding to circuit noise as to if it will read as a high or a low. One thing you can do to prevent that floating condition is to turn on the internal pull-up resistor for each pin you want to play with. That way it will read as a steady 1 with nothing connected to the pin, and read as a 0 if you wire a jumper (or switch) wired to a ground pin.

Here is how you enable the pull-up:

pinMode(s3, INPUT); // set the pin as a input pin
digitalWrite(s3, HIGH); // this turns on the internal pull-up for this pin

Lefty

3

Ah - I'm with you. Fantastic thank you.

Nick