is to dump any excess current as heat before it goes to ground,
My question is if you use a 220 ? resistor on one LED could you use a 2.2k ? resistor and tie 10 LEDs to it?
Like all math we can make the "proportion" bit into an equals if we put in a constant of proportionality, like this:-V = k * IThe constant of proportionality is called "resistance" and so we write :-V = R * I
and the current is the 40Ma the pin puts out?
if it is 3.3V=220?*40Ma,
how do you multiply ohms by Milliamps and come out with an answer that makes sense?
Quoteis to dump any excess current as heat before it goes to ground, No it is not.It is to drop the excess voltage and approximate a constant current drive.
Okay NOW I think I understand why you would need a LOWER resistance for 10 LEDs than for 1 (3.3V=x*150Ma(10 LEDs*15Ma each)). Therefore x=a 33? (or the next larger value)resistor.Still wrong?
Also, I am assuming ...... that 15Ma is the amount of current needed for an LED to turn on.
QuoteOkay NOW I think I understand why you would need a LOWER resistance for 10 LEDs than for 1 (3.3V=x*150Ma(10 LEDs*15Ma each)). Therefore x=a 33? (or the next larger value)resistor.Still wrong? The maths is right but the electronics behind it is wrong. You can not use one resistor for more than one LED because the forward voltage drop of each LED is slightly different. So therefore each LED needs its own resistor.
QuoteAlso, I am assuming ...... that 15Ma is the amount of current needed for an LED to turn on.For a start it is milli Amps mA not mega Amps MA. Second no there is no set amount of current to turn on an LED, the smaller the current the dimmer it is. I have a white LED that is too bright to look at directly when it only draws 3mA. It depends on the specific LED. There is however a minimum voltage required to turn it on, normally called the forward voltage drop.
Yeah, this is the usual consideration, but have you ever actually tried using just 1 series Rfor multiple Leds? I'm just curious as to the actual results.
Maybe if running at more than half the maximum current one LED will have too much current and burn out a lot quicker.
32Mhz (forgive the capitalized M if it is incorrect please) instead of 16Mhz
At some levels it is as much an art as a science.
I was about to start a thread on this very topic, but apparently it has been asked before! After reading through the thread (and the links posted therein), I have a couple of questions:1. When performing Ohm's Law calculations, what specifies the values for V and I?V, to me, should be the supply voltage (3.3V or 5V would be what I'm using in this case). And should I be the maximum allowable current to pull from the pin? Just wanting to make sure... 40ma is absolute maximum, but 20-30 ma is a better maximum limit standard to stick to. Keep in mind due to internal resistance of the output pins the output voltage will sag as current draw from the output pin is increased. Just shows that there is a difference from fundamental principal and electrical reality of real world components. That is why the datasheet for devices are so important to study and understand a chip limits and capabilities. 2. What is the maximum allowable current draw for the 5V pin on an Arduino Uno? From this page, I see 50mA for the 3.3V pin, but nothing is listed for the 5V pin.Because there is no exact answer. If the board is being powered via USB then there is a 500ma thermofuse that sets a maximum limit for the board and anything you wire up to it. But if powered from an external DC voltage source then there might be somewhat more but it depends on the exact DC voltage input as there is a heat dissipation limit for the on-board 5vdc voltage regulator. So hard answers are desirable but often allusive in the real world.3. Can one model a switch/pushbutton similarly to an LED? I ask this because a switch also has "infinite" resistance when not activated, but near 0 resistance when pressed.No, totally different components, and a switch doesn't share all the characteristic of a switch and visa versa.
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