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Specs for the parts in the starter kit
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Specs for the parts in the starter kit

by blovegro on Thu May 19, 2016 5:52 pm

Are specs or data sheets available for the parts in the starter kit? In particular, the specs on the LED's to correctly size current limiting resistors.

blovegro
 
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Re: Specs for the parts in the starter kit

by adafruit_support_mike on Fri May 20, 2016 5:01 am

You can probably find the datasheets in the bare LEDs section, but you don't really need them to calculate LED resistors.

The color of light that comes out of an LED is directly related to the LED's forward voltage. Red LEDs always have a forward voltage around 1.7v, green LEDs always have a forward voltage around 2.1v, and blue LEDs always have a forward voltage around 3.1v.

You can make a red LED emit green light (briefly, before it becomes a smoke-emitting diode) by sending enough current through it to raise the forward voltage to 2.1v.

If you're working from a 5v supply and want about 25mA through your LEDs (the nominal current for all indicator LEDs), use a 150 ohm resistor for reds, 120 ohms for greens, and 82 ohms for blues.

In practice that will be pretty bright, especially for the blue ones. Using a 1k resistor for all LEDs, regardless of color, usually works well.

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Re: Specs for the parts in the starter kit

by blovegro on Fri May 20, 2016 7:43 am

All of this is good general advice, but not exactly what I asked. I want to be able to calculate a maximum brightness current limiting resistor (or the allowable range for the current limiting resistor, if you want to think of it that way), not an approximate answer.

I had troubles finding the bare LED's in the catalog (searching LED returns 32 pages of results), but I went back and found them and found the following specs, which do not agree with what you said. The green turn-on voltage is suspiciously high, very different from what you listed, and the blue turn-on voltage you gave is outside of the range listed.

A quick look at the Digikey catalog shows green LEDs over a range from 2-20 mA typical current and 1.8-3.4 volts turn on. Your advice might be OK for LEDs from the Adafruit catalog but misleading for parts from other sources.

I would still be interested in a manufacturer data sheet for the LEDs. Here are the specs provided online for the super-bright LEDs:

◦ Pack of 25 clear red LEDs
◦ 5mm diameter
◦ 640 nm wavelength
◦ 1.8-2.2V Forward Voltage, at 20mA current
◦ 1500 mcd typical brightness
◦ Viewing Angle : ±10 degrees
◦ Maximum continuous current: 30mA


◦ Pack of 25 clear green LEDs
◦ 5mm diameter
◦ 520 nm wavelength
◦ 3.2-3.8V Forward Voltage, at 20mA current
◦ 8000 mcd typical brightness
◦ Viewing Angle : ±10 degrees
◦ Maximum continuous current: 30mA

◦ Pack of 25 clear blue LEDs
◦ 5mm diameter
◦ 465 nm wavelength
◦ 3.2-3.8V Forward Voltage, at 20mA current
◦ 6000 mcd typical brightness
◦ Viewing Angle : ±10 degrees
◦ Maximum continuous current: 30mA

blovegro
 
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Re: Specs for the parts in the starter kit

by blovegro on Fri May 20, 2016 7:49 am

By the way, I note that the LED tutorial (below) has a link to the Red data sheet. I suggest the catalog page link to this data sheet as well, and for green and blue as well.

https://learn.adafruit.com/all-about-leds/overview

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