Ohm's Law does not apply to LEDs. LEDs are not resistors. They are very non-linear devices whose characteristics vary greatly. Especially between different colour of LED.Not even a remote possibility. Do the math. Or actually measure current as I have done. It's called Ohms Law not Ohms Suggestion.
I believe the correct information is maximum 16ma per pin, but all GPIO pins must not exceed 51 mA so for all data pins that would be an average of 3 mArurwin wrote: If I remember correctly the maximum current from all of the GPIO pins together is 16mA and any one of them can supply that current if none of the others are used.
I asked first and anyway not inclined to do your homework for you ATM. But did take a minute to pull a common LED out of the junk box and connect direct from pin 8 (hard high) to ground and measured 6.9ma. So we are not even close to the pin limit and could hook up quite a few with no resistors at all and still not violate package limit. Or anywhere near over-driving the LEDs themselves.Heater wrote: Ohm's Law does not apply to LEDs. LEDs are not resistors. They are very non-linear devices whose characteristics vary greatly. Please show your math workings.
After your edit I see now where you pulled the100ma number from (except for yellow which is anomalous) but it's unrelated to the subject at hand involving connecting across I/O not across power supplies. It would be amazing if you could really draw even 1/10th that. Weird how many think you can draw amps from an MCU pin.gordon77 wrote:i took a selection I have to hand
across 3.3v no resistor
Duh... Of course these pins have internal limit. Exactly my point. In fact all power supplies and batteries (even car/Pb) have internal resistance. The question is how much and what is the resulting current allowed. Both math and experiments back up what I say about Pi pin current into an LED. Which is more than enough so time to move on to other subjects.gordon77 wrote:Unless the pi has some kind of internal current limit or internal resistance in the GPIO source then l still say you risk the GPIOS failing by running an led with no resistor.