Arduino output voltage not stable

Projects General Guidance
1

Hello!
I have a Genuino UNO.
I am having trouble with unstable voltage output when using pin 9.
This is my program

void setup() {

pinMode (9,OUTPUT);

}
void loop() {

analogWrite(9,255);

}

When I am measuring between pin 9 and GND, I am getting 4,85vDC or 5,15vDC, just depends on what time on the day I am measuring... It's not unstable when I'm measuring it, so either 4,85 or 5,15vDC.

I am using my USB cable from my computer, which I'm measuring a stable 5,22vDC.

I've done some tests now, and when I am connecting pin 9 and GND to my 0-10v PWM converter, I am getting even lower voltages.

For example:
When I have 5,15vDC on pin and GND, I am getting 4,85 when I connect them to the converter.

Can anyone help me?

2

Your controller does not have any analog output. What you measure is the 5V supply voltage. Dunno what makes that voltage differ from the USB supply voltage, a scope may reveal more details.

3

Digital pins are either high or low and 4.85V or 5.15V are both high.

On a 5V board like the Arduino Uno, a voltage greater than 3.0V is a high. On a 3.3V board, a voltage greater than 2.0V is a high.

4

Voltage from PC via USB goes thru a PTC Resettable fuse, which has a finite resistance. Current thru the resistor creates voltage which feeds the VCC pin, which then goes thru an output drive transistor, which also has a resistance (Rds) when turned on.
So, the voltage you see will be lower than what the PC outputs, and will vary by the amount of current draw by the board overall, and by the specific output load.

5

Any reason for why it's not 5.0v?

6

Digital pins are high impedance They are NOT a power source. The load of the voltmeter could easily pull the voltage down a bit.

You are troubleshooting a normal condition.

7

Many possible reasons, please supply more details. A scope could reveal more.

8

Voltage drop across the PTC resettable fuse, voltage drop across the output transistor. I thought I stated that pretty clearly.

9

How much CURRENT does the converter draw from the output pin?
Post a diagram showing how EVERYTHING is connected.

10

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.