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Only getting 2.75V from Pin 5
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Only getting 2.75V from Pin 5

by tlschumacher2000 on Thu May 28, 2020 11:17 pm

I'm running the Strandtest for the M4 and seeing nothing. I've verified the ws2812b string is working by plugging it into a Pro Mini.
So I decided to see if the ItsyBitsy M4 was putting out 5V on pin 5 with this program.
#define PIN 5 // this is the 5v output pin
#define ledPin 13

void setup() {
// put your setup code here, to run once:
pinMode(ledPin, OUTPUT);
pinMode(PIN, OUTPUT);

}

void loop() {
// put your main code here, to run repeatedly:
digitalWrite(ledPin,HIGH);
digitalWrite(PIN,HIGH);
delay(3000);
digitalWrite(ledPin,LOW);
digitalWrite(PIN,LOW);
delay(3000);
}

When I put a volt meter between pin 5 and ground, it goes between 0 and 2.74v then back to 0.
Am I missing something here? I thought Pin 5 was the high voltage output so I could drive the LED strip directly.
Inquiring minds would like to know.
Terry

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Re: Only getting 2.75V from Pin 5

by dastels on Thu May 28, 2020 11:33 pm

D5 is level shifted to whatever the supply voltage is: 5v if you have USB connected, that will be close to 5v, a bit less than the battery voltage if you just have a battery connected.

Dave

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Joined: Tue Oct 20, 2015 3:22 pm

Re: Only getting 2.75V from Pin 5

by tlschumacher2000 on Sat May 30, 2020 12:22 am

Thanks Dave
Upon further investigation, I discovered those voltages were with USB and the light strip WAS connected. If I disconnected the lightstrip the voltage was back up to 5v.
I'm not sure the strip should be pulling it down like that. More investigation is needed.
Terry
(how do I mark the question as solved? I have another posting that was solved also)

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Posts: 4
Joined: Sat May 16, 2020 12:48 pm

Re: Only getting 2.75V from Pin 5

by adafruit_support_bill on Sat May 30, 2020 6:07 am

Pin 5 is a GPIO pin. It can put out 5v logic levels, but it is not capable of supplying enough current to power a strip. You should power your strip from the USB pin and use pin 5 as your signal pin for the strip.

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Please be positive and constructive with your questions and comments.