0

mini pushbutton with led
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

mini pushbutton with led

by pbuelow on Wed Sep 11, 2019 9:02 pm

The two buttons, 3104 and 3105 are somewhat tricky to use. The datasheet has not data on the LED embedded, so why use a 1K? I see the current rating at .1, but what is the forward voltage? I want to put a resistor in and then PWM to allow for dimming, but without some more data, it's hard to know what to use. Can someone provide the LED data?

Also, these things are really touchy. I was testing them, and burned out 4 of them way too easily. Thankfully, I bought extra, but it shouldn't be so easy to watch them flame out. I suspect it was due to me using a 100 ohm resistor instead of a 1k running off the 3v3 line of a an RPi. I've moved to a 1k, and haven't burned any more out. Can I get these replaced?

pbuelow
 
Posts: 43
Joined: Sat Oct 04, 2014 2:43 pm

Re: mini pushbutton with led

by dastels on Thu Sep 12, 2019 9:17 am

Please see https://learn.adafruit.com/all-about-leds for information on how LEDs work and how to use them. You need an appropriate resistor to limit the amount of current going through the LED. Too much current and the LED will be destroyed, often violently. They're not really "touchy", you just need to treat them properly.

dastels
 
Posts: 718
Joined: Tue Oct 20, 2015 3:22 pm

Re: mini pushbutton with led

by pbuelow on Thu Sep 12, 2019 4:42 pm

Yeah, I get that. However, the datasheet provided doesn't actually have anything useful about the LED. The product page lists it's current as 10 ma, but other than that, what's the forward voltage, brightness, other things usually in a datasheet? How do you size the resistor? 1k at 3v3 is huge for an LED, but that seems to work. Why is that? What is the nominal input voltage for this thing? The product picture shows voltage in, but is that 3, 5, or 12v (I suspect this LED is bulit for 12v, but that's a guess). A 200 ohm resistor should not blow out an LED at 3v3, but it did to at least one. 1K works, but I can't explain why.

pbuelow
 
Posts: 43
Joined: Sat Oct 04, 2014 2:43 pm

Re: mini pushbutton with led

by dastels on Thu Sep 12, 2019 5:10 pm

With it lit with the 1K resistor, you can measure the voltage across the LED. That will be constant. That gives you the voltage across the resistor, which will give you the current. Then for other supply voltages, you can gauge what resistor you need.

dastels
 
Posts: 718
Joined: Tue Oct 20, 2015 3:22 pm

Please be positive and constructive with your questions and comments.