Arduino Mega Pins staying high

Development Tools IDE 1.x
1

Hello all,

I have an Arduino Mega and several of the pins (19-21) are registering as 5 volts on my multimeter when I have them set to LOW "digitalWrite(19, LOW)" in the code.

Is there something I am doing wrongly?

TIA

2

Did you declare them as outputs in void setup() ?
pinMode(19, OUTPUT);
for example.

3

I have them declared as INPUTs since I intend to hook them up to IR light gates.

Inside void setup():

#define PINsensor1 19
pinMode(PINsensor1, INPUT);
4

Well there you go then.

If they are Inputs and you set them Low, I believe the code disconnects the internal pullup resistors.
You need to declare them as Outputs for digitalWrite to actually drive them high or low.

5

Thank you, CrossRoads, that does make sense.

I was worried perhaps the pins were damaged. :sweat_smile: