Odd digital pin reading

Projects General Guidance
1

Hello,

I have a piece of plastic, resting at 10 degrees off vertical, that has 2 holes drilled in it.

I have a patch wire attached to ground on an Arduino YUN, with the other end poking through one hole on the plastic board.

I have another patch wire attached to digital pin 2 (configured in the sketch as INPUT_PULLUP) on the Arduino, the other end of which is poking through the other hole on the plastic board.

The distance between the pins is a few mil less than the diameter of a penny coin.

The following code sketch is running on the Arduino:

#define START_PIN 2
#define MAX_PINS 1

void setup() {
Serial.begin(9600);
for ( int pin = START_PIN; pin < START_PIN + MAX_PINS; pin++) {
pinMode( pin, INPUT_PULLUP);
}
}

void loop() {
for ( int pin = START_PIN; pin < START_PIN + MAX_PINS; pin++)
{
Serial.print( getState( pin));
Serial.print("\t");
}
Serial.println();
delay(1000); // delay in between reads for stability
}

char* getState( int pin)
{
if ( digitalRead( pin) == 0)
return "HERE";
else
return "gone";
}

I place a penny on the board resting on the 2 protruding patch wires, the output is “HERE”, I lift the coin up a little and “gone” is output.

All good … but if I flick the coin up to open the ‘switch’ and let it drop back onto the patch wires again, sometimes I will receive “gone” from all subsequent outputs on the serial monitor.
This state will continue until I move the coin off and then on the wires.

Could anyone tell me why this is happening and whether there is a possible fix?

Andrew

2

What is the purpose of the FOR loop if you have only one pin to test?

It sounds to me as if the coin just is not making a good contact with your wires - have you tried cleaning the coin with fine sandpaper?

...R

3

The real project will work with 8 coins so the for loop will iterate over each pin. I will try cleaning the coins, thanks for your advice.