votage digital pin

im totally confused, im new with arduino. What im confused about is when it is HIGH it should be 5v (connect with usb), but when I measure it using voltmeter, it was 3.3v. what is the actual output voltage on digital pin actualy. im using arduino uno

Show us the code that enabled the pin.

Which Arduino? pinMode?

Is there anything connected to the output (other than the multimeter)? The "black" lead of your multimeter is connected to the Arduino ground, right?

Are you getting 5V on the 5V pin?

A low-impedance load (or an incorrect connection) can "pull-down" the voltage. It should be very-close to 5V with no load. When you write LOW, does it go to nearly zero?

Just for reference, anything above 3.5V (0.7 x Vcc) on an input is defined as high and anything below 1.5V (0.3 x Vcc) is defined as low. Anything in-between is undefined.

0.6 x Vcc is the threshold for an Uno powered at 5V, ie above 3.0V is high.

It's only 0.7 when the chip is powered from less than 2.4V.

check +5v on 5v pin if it is about 5v check your code about pin mode and digital Write. measure voltage without any load.

im using uno board. the pin that i used was 13 (one of them). in tutorial in youtube mentioned when it is HIGH then the Voltage to the pin will be the same as the supply eg 5v. then i wonder can the io pin connect to 5v relay..?

You want to drive the relay's coil with 5V? There are small telecon relays that only need 11-17mA to drive them. Most however need more current so an Arduino output pin is not suitable. A simple transistor buffer will do.

If you drive a relay from an Arduino pin you must ensure the relay coil takes less than about 25mA, and provide a schottky diode free-wheel diode across the coil to protect the Arduino pin protection diode.

If you take 40mA from an Arduino pin (its absolute maximum), its voltage drops perhaps to below 4V, which will not reliably operate a 6V relay. Its very bad practice to strain an output to its maximum anyway, so treat the limit as 25mA. Above that use a transistor and free-wheel diode (ordinary diode will do then).

HafizSuhanda:
im using uno board. the pin that i used was 13 (one of them). in tutorial in youtube mentioned when it is HIGH then the Voltage to the pin will be the same as the supply eg 5v. then i wonder can the io pin connect to 5v relay…?

Doesnt pin 13 have the built in LED on it so is the forward voltage drop on the led causing the low reading?

DonRecardo: Doesnt pin 13 have the built in LED on it so is the forward voltage drop on the led causing the low reading?

No. Pin13 of an Uno R3 is buffered by an LM358 opamp. The opamp drives the LED. Leo..