General > General Technical Chat
Software guys, please, no.
<< < (20/27) > >>
sokoloff:
I'm trying to guesstimate in my head the answer to: "Among beginners wiring up their first breadboard Arduino or Raspberry Pi blink an external LED project, what percentage of them use a dropping resistor?"

I'd be pretty surprised if it was over 80% and shocked if it was over 95%.

Then, trying to guesstimate the answer to "Among people wiring an external LED across a Raspberry Pi GPIO pin and ground and blinking it, what percentage of those will result in damage to the Pi?", I'd be shocked if the answer was over one in a thousand.
ledtester:

--- Quote from: pcprogrammer on September 21, 2022, 12:15:50 pm ---If I was a beginner with not a lot of money to spend on my hobby, I would be very pissed if my 35 dollar board went poof because someone showed in a youtube video that it is ok to stick a LED directly on to the pins without explaining why it works for him.

--- End quote ---

A user comment from the video:



Howardlong:

--- Quote from: ledtester on September 21, 2022, 02:02:23 pm ---
--- Quote from: pcprogrammer on September 21, 2022, 12:15:50 pm ---If I was a beginner with not a lot of money to spend on my hobby, I would be very pissed if my 35 dollar board went poof because someone showed in a youtube video that it is ok to stick a LED directly on to the pins without explaining why it works for him.

--- End quote ---

A user comment from the video:



--- End quote ---

That's ~40mW dissipated on each port's mosfet trying to be a resistor. Bear in mind that a typical 0603 resistor is rated at 63mW and the mosfet driver transistor is several orders of magnitude smaller...

Each port is rated for 16mA max, 51mA total aggregated across all ports. The ports are configurable down to 2mA, but this is designed for limiting switching noise by limiting slew rates, not for driving LEDs.

I measured 27mA with a red LED with default settings. Others have measured over 200mA shorted (I'm not going to try), so so much for being "current limited" to 16mA.

langwadt:

--- Quote from: Howardlong on September 21, 2022, 07:05:22 pm ---
--- Quote from: ledtester on September 21, 2022, 02:02:23 pm ---
--- Quote from: pcprogrammer on September 21, 2022, 12:15:50 pm ---If I was a beginner with not a lot of money to spend on my hobby, I would be very pissed if my 35 dollar board went poof because someone showed in a youtube video that it is ok to stick a LED directly on to the pins without explaining why it works for him.

--- End quote ---

A user comment from the video:



--- End quote ---

That's ~40mW dissipated on each port's mosfet trying to be a resistor. Bear in mind that a typical 0603 resistor is rated at 63mW and the mosfet driver transistor is several orders of magnitude smaller...

Each port is rated for 16mA max, 51mA total aggregated across all ports. The ports are configurable down to 2mA, but this is designed for limiting switching noise by limiting slew rates, not for driving LEDs.

--- End quote ---

and I believe the variable drive strength is implemented by each pin being made up of several parallel mosfets and only turning on some of them

coppice:

--- Quote from: ledtester on September 21, 2022, 02:02:23 pm ---
--- Quote from: pcprogrammer on September 21, 2022, 12:15:50 pm ---If I was a beginner with not a lot of money to spend on my hobby, I would be very pissed if my 35 dollar board went poof because someone showed in a youtube video that it is ok to stick a LED directly on to the pins without explaining why it works for him.

--- End quote ---

A user comment from the video:



--- End quote ---
Where do people get the idea there is current limiting. Are they confusing this with variable drive strenth?
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod