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Topic: Using Resistors with LEDs (Read 8087 times) previous topic - next topic

Paul__B

1 k != 135 ohms
No, but with modern LEDs 2.5 mA will be plenty visible but will not burn your eyes.  And it certainly won't burn anything else.  :smiley-lol:

raschemmel

A LED can't burn your eyes or they wouldn't sell them.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

aarg

#32
Mar 15, 2015, 11:15 pm Last Edit: Mar 15, 2015, 11:20 pm by aarg
Look at the value of LED current limiting resistors RN2A, RN2B and RN2C on the UNO. 1.0K.

;)
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

nickgammon

Nevermind that 1 k is the wrong value. We can address that when he learns to wire his circuit correctly.
As I mentioned earlier when I tested with different resistances, I could hardly tell the difference visually between 1k and 100 ohms. So 1k would "work" and use less current.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

raschemmel

Quote
100 ohms. So 1k would "work" and use less current.
can't argue with that
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

christop

A LED can't burn your eyes or they wouldn't sell them.
I don't think he meant it literally. Super-bright LEDs (particularly the blue ones, in my experience) really are quite bright unless there's very little current--a milliamp or so--running through them. They're bright enough to be painful and cause at least temporary blindness if you look directly into the LED.

raschemmel

Quote
They're bright enough to be painful and cause at least temporary blindness if you look directly into the LED.
Oh, I didn't know that. Maybe that's why I can't see out of my right eye... ;D
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

christop

Oh, I didn't know that. Maybe that's why I can't see out of my right eye... ;D
"Caution: Do not look into laser LED with remaining eye." :D

Paul__B

Look at the value of LED current limiting resistors RN2A, RN2B and RN2C on the UNO. 1.0K.
And they are annoyingly bright!

Especially on some of my Nano clones with a white "L" LED.

Having a bright power indicator is unnecessarily distracting.

JimboZA

I've had some new leds resistored down to something like 5mA and still too bright for the purpose at the time. And on one of my DFR shields I stuck a piece of card over an indicator: the light spilling out the side is more than enough to say "I'm on"....
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Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

raschemmel

#40
Mar 16, 2015, 05:42 am Last Edit: Mar 16, 2015, 05:43 am by raschemmel
What can I say, I like bright lights and I don't use batteries unless I need to. (-:
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

electricalhobbyist

depending on the total current the LED will consume, at a certain current, the LED will not light. make sure to calculate the maximum possible current that will flow in the resistor. LED has a minimum voltage to work..

raschemmel

Quote
LED has a minimum voltage to work..
AKA "Forward Voltage" (Vf)
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

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