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by ModernWires
Sun Aug 11, 2019 9:57 am
Forum: Beginners
Topic: Is it safe to connect the GND pin to the GND of an external USB psu?
Replies: 2
Views: 226

Is it safe to connect the GND pin to the GND of an external USB psu?

Is it safe to connect the GND pin of the raspberry pi (I'm using the new pi 4b specifically) to the GND of another USB power supply like shown below? I want to turn on and off a mosfet based on the output of a gpio pin. I don't want to use the on board USB or the 5V pin to power the load because I'm...
by ModernWires
Sat Aug 03, 2019 1:30 pm
Forum: Troubleshooting
Topic: 3B+ suddenly died with no video out and solid act led
Replies: 10
Views: 502

Re: 3B+ suddenly died with no video out and solid act led

A GPIO can safely provide 16mA. 16mA through 51Ω would mean about 0.8v across it, so the LED would have to have 2.5v across it. Thanks. Good to know. I probably should use a separate power rail to power everything anyway. The buzzer is most likely also drawing over 16mA. Maybe I can get one of thos...
by ModernWires
Tue Jul 30, 2019 3:01 pm
Forum: Troubleshooting
Topic: 3B+ suddenly died with no video out and solid act led
Replies: 10
Views: 502

Re: 3B+ suddenly died with no video out and solid act led

You need a resistor between the GPIO and the LED (or between the LED and GND) to limit the current. Too much current can damage the GPIO circuitry inside the SoC, and that damage can spread. LEDs are not straight-forward devices - up to a certain voltage, almost no current passes, but above that vo...
by ModernWires
Tue Jul 30, 2019 4:24 am
Forum: Troubleshooting
Topic: 3B+ suddenly died with no video out and solid act led
Replies: 10
Views: 502

Re: 3B+ suddenly died with no video out and solid act led

I previously connected a led and a buzzer and everything worked just fine until I tried to boot it up yesterday. How did you connect those? Taking too much current from a GPIO, or letting more than 3v3 near a GPIO can damage the SoC https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=58151 is u...
by ModernWires
Tue Jul 30, 2019 4:14 am
Forum: Troubleshooting
Topic: 3B+ suddenly died with no video out and solid act led
Replies: 10
Views: 502

Re: 3B+ suddenly died with no video out and solid act led

HypnoToad wrote:
Mon Jul 29, 2019 2:21 pm
What voltage do you get if you measure between GND and PP9?
I got 1.8v.
by ModernWires
Mon Jul 29, 2019 1:08 pm
Forum: Troubleshooting
Topic: 3B+ suddenly died with no video out and solid act led
Replies: 10
Views: 502

Re: 3B+ suddenly died with no video out and solid act led

Pull the SDCard. Power on. Does it do the same thing? Does any part of your RPi get too hot to touch very quickly? Have you been abusing GPIO pins? Can you measure the voltage between Pin#1 & GND (use the case of the USB or ethernet to avoid shorting pins)? Can you do the same for Pin#2 (or Pin#4)?...
by ModernWires
Mon Jul 29, 2019 11:46 am
Forum: Troubleshooting
Topic: 3B+ suddenly died with no video out and solid act led
Replies: 10
Views: 502

3B+ suddenly died with no video out and solid act led

My 3B+ suddenly stopped working yesterday. When I power it on I get two solid leds and they just stay on forever without blinking or anything. I checked the sticky thread but it didn't seem to cover the case where the act led doesn't blink at all. I guess it means the pi can't read from the micro sd...

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