digitalWrite and analogWrite deliver 3.03 V in higher state

Other Hardware General Electronics
1

I guys,
Here is my problem, my arduino uno deliver 3.03V insted of 5V when I try a digitalWrite(pin, HIGH) or an analogWrite(pin, 255).
There is no big charge, and the problem appened in both alimentation mode, USB and external alimentation via an ATX power supply delivering 5V.
I'm a newbie, but I really don't understand why I can't have 5V, moreover, I really need 5V for my circuit, the transistor need 5V to work properly. :frowning:

I hope it's clear, sorry for bad language
Light

2

It could be you're trying to draw too much current, causing the voltage to drop (and possibly damaging the output pin drivers).
Can you please supply a schematic?

3

Yes, its important not to take 40mA or more from a pin - in fact best to keep this down to 25mA or so for peace-of-mind - but the output voltage will drop if heavily loaded even at that level. The output transistors are about 40 ohms when on so a 10mA load will mean the output is closer to 4.5V than 5.0V.

Prolonged over-loading of the output transistors will damage the chip because through local overheating, Short-term overloads may or may not cause obvious damage, there is no guarantee.

4

I don't think that the board is heavily loaded, this is the schematic Arduino Playground - HomePage, I just had a DEL on the arduino output pin....

5

I just had a DEL on the arduino output pin....

A Diesel-Electric Locomotive?

6

French spotted, a LED sorry :wink:

7

But you had a current-limiting resistor as well, not just a LED?

8

Yep, of course, 100 ohm resistor a 2W one. There is another IR LED, with a 1K resistor, 2W too . The white LED is not on the same pin with the IR LED, so I don't think that the board is over load with 2 LED...

9

Where did you measure the 3V at? What was the physical points you were touching?

10

Did you measure a voltage when nothing connected to the board?
And, have you declared pin as OUTPUT in your code?

11

void setup() {
Serial.begin(9600);
pinMode(12, OUTPUT);
}

void loop() {
digitalWrite(12, HIGH);
}

I tested it with this code, I have 5V between pin 12 and pin gnd, but if i put a LED between the two pins, i have only 3V between the 2 pins, even if I use an external alimentation ( ATX ) is this normal ? If it is, how can I get 5V in OUTPUT with the LED, to saturate correctly my transistor ? :~

12

I = V / R = ( 5 - 1.4 ) / 100 = 36 mA. Current is too high for arduino output, try 200 Ohm, you should not expect 5V, but 4.2V is normal with 20mA current

13

Light411:
but if i put a LED between the two pins, i have only 3V between the 2 pins

With a resistor, this would be expected. LEDs only drop their forward voltage.

Light411:
even if I use an external alimentation ( ATX ) is this normal ?

What is an alimentation? That word isn't translating correctly.

14

Here's what "alimentation" means. However I don't think it's the right english word, unless Light411 is refering to externally provided power...