General > General Technical Chat
Software guys, please, no.
fourfathom:
--- Quote from: pcprogrammer on September 20, 2022, 03:53:11 pm ---But he uses two LED's. One that is placed in the breadboard. No extended wires, and it looks like just a standard green LED.
And the statement "No resistor for 3.3V" is challenging. Take a 3.3V power supply and hook the same LED on to it. My money is on bye bye LED. With a forward voltage of around 2V the current will go up and up.
--- End quote ---
I didn't see the bare LED in the protoboard. OK, so no resistor. Definitely not right, but also definitely not the same thing as connecting the LED across a 3.3V power supply. Most IO pins can handle the occasional short to ground without smoking, and a bare LED is less of a load than that. The available current will probably be well under 10mA so the LED will also survive. "No resistor" is bad advice, but it's probably still going to work. I just don't see the outrage -- the guy was wrong, but so what?
pcprogrammer:
--- Quote from: Howardlong on September 18, 2022, 11:07:58 am ---FWIW, I took a measurement of 27mA for a red LED without a resistor on a GPIO.
The SoC GPIO current limits are for power limiting during transients, not for driving LEDs.
Yes, it works, most of the time. So does driving home drunk. Just because you can doesn't mean you should.
--- End quote ---
Well it can be more then 10mA according to a test Howardlong did.
pcprogrammer:
--- Quote from: tooki on September 20, 2022, 04:04:08 pm ---That's clearly a modern emerald green (~520nm) LED, and those have significantly higher forward voltages (3-3.5V) than traditional lime green LEDs. So when connected to a 3.3V power source, many of them are right in their happy place, even without a current limiting resistor.
If we were talking about old-fashioned 1.7-2.2V LEDs, then it'd clearly be problematic. But with modern 3V+ green/blue/white LEDs, it's actually not preposterous.
--- End quote ---
Well that shows that I have been out of the real hardware game to long. I knew blue LEDs had higher forward voltages, but not that there are new types of green that have higher forward voltages.
Thanks for the bringing my knowledge up to par a bit :-+
borjam:
--- Quote from: Howardlong on September 17, 2022, 11:36:22 pm ---Timestamp 3:10, hooking up a jelly bean LED directly to a Raspberry Pi GPIO deliberately without a resistor: deliberately because, well, it works for him, and he asks viewers to convince him otherwise.
--- End quote ---
I remember a guy in the early 90's who asked for help because his server used to crash on heavy I/O. I went there and I pointed out that there was no SCSI terminator. He said "it works without it".
I answered "OK! And I left".
rdl:
I didn't watch the video. Did the LED actually get get mentioned or described? Because you can get LEDs with internal resistor to run from a specific voltage. I have some and have to mark them with a Sharpie to tell them from regular LEDs. They're really useful for breadboarding.
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