Netduino home hardware projects downloads community

Jump to content

The Netduino forums have been replaced by new forums at This site has been preserved for archival purposes only and the ability to make new accounts or posts has been turned off.

Enhance RGB Led with Transistors

rgb led transistor resistor

  • Please log in to reply
2 replies to this topic

#1 tridy


    Advanced Member

  • Members
  • PipPipPip
  • 68 posts
  • LocationStockholm, Sweden

Posted 16 June 2015 - 07:58 AM

I have got some of the RGB Leds with common cathode, that I would like to experiment with:


Attached File  rgb_led_cathode.png   50.46KB   0 downloads


I went through some of the postings on the forum (like http://forums.netdui...ed-pwm-sample/)and made it work with 500 ohm resistors to be on the safe side (as far as I undestand).


It seemed to me that setting the same values for different colors do not produce the same brightness. If I look at the specifications of the RGB Led from Sparkfun, it looks like there are different voltages for each color, so it would probably require a different resistor for each color.


I found that CW2 wrote in the posting that for the best result, it is better to add transistors, and Embedded Lab post shows using 1 rgb led, 3 transistors and 6 resistors (this is a "common Anode" version of RGB led):





For the sake of trying to make it work "better", I would like to know how to do the calculation of what kid of transistors and what kind of resistors (when both are involved) I need in a little bit more details. Could someone help me wit that?



#2 Nevyn


    Advanced Member

  • Members
  • PipPipPip
  • 1072 posts
  • LocationNorth Yorkshire, UK

Posted 16 June 2015 - 08:15 AM

There's a very old blog post of mine looking at using a transistor as a switch to control and LED.


Hope this is useful,


To be or not to be = 0xFF


Blogging about Netduino, .NET, STM8S and STM32 and generally waffling on about life

Follow @nevynuk on Twitter

#3 tridy


    Advanced Member

  • Members
  • PipPipPip
  • 68 posts
  • LocationStockholm, Sweden

Posted 16 June 2015 - 11:11 AM

Thanks. I will take a look and get back with the results.

Also tagged with one or more of these keywords: rgb, led, transistor, resistor

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

home    hardware    projects    downloads    community    where to buy    contact Copyright © 2016 Wilderness Labs Inc.  |  Legal   |   CC BY-SA
This webpage is licensed under a Creative Commons Attribution-ShareAlike License.