MEGA 2560 pins at 3.3vdc when set to HIGH.

Development Tools IDE 1.x
1

Hi, maybe this has been answered but I couldn't find anything.

When pin 10 on my mega is HIGH I get 3.3 volts. Is this because it is a special PWM pin?

Pin 22 is 5v when HIGH so I just switched pins, but I was hoping for an explanation and possible work around if I needed to use that pin at 5v.

Thanks for reading, I apologize if this is obvious or previously answered, I did search google and the forum before posting.

//This will produce 3.3vdc at pin 10 and 5vdc at pin 22 on my MEGA 2560
void setup() {                
  // initialize the digital pins as an outputs.
  pinMode(22, OUTPUT);  
  pinMode(10, OUTPUT);    
}

void loop() {
  digitalWrite(22, HIGH);
  digitalWrite(10, HIGH);

}
2

I would expect close to 5V output on both pins with that code.
Is D10 connected to anything offboard?

3

It's connected to a 5VDC relay. Pin 22 has no problem engaging the relay with this code, but 10 will not. when I attach my multimeter pin 10 has 3.3v, and 22 has 5v.

I have had this happen when I done this in my setup, but I assumed it was a function of the arduino:

void setup(){
pinMode(10, OUTPUT);
digitalWrite(OUTPUT, LOW) 
}

I had LEDs hooked up to the output pin and it would only dimly turn them on. When I removed the digitalWrite everything worked properly. But this time I didn't do that, and I'm still only getting 3.3VDC on pin 10.

I see a lot of posts with people trying to get 3.3vdc from a digital out. I should just give them my MEGA. LOL.

4

I should clarify that when the setup had the digitalWrite(10, LOW) and the led would only turn on very dim, it was an uno, and a completely different project.

5

That last case sounds like missing pinMode tho.

The earlier one:

void setup(){
pinMode(10, OUTPUT);
digitalWrite(OUTPUT, LOW); <<< change 'OUTPUT' to '10'
}