Science Buddies: "Ask an Expert"

Hi!

This is for science fair. Due date: October 20, 2014

I'm having difficulty getting my RGB LED clear common cathode to light up. I've tried using example sketches from a couple of different sources like the arduino forum and seeed studio.

I'm wondering if I have it wired correctly. I am using a breadboard. The leads of my LED are in pins 7, 8,9, and 10 (red, ground, green, blue). In the same horizontal row, I have a 330 Ohm resistor for each lead (red, green, blue). For the ground lead on the LED, I have jumper that goes from Row 8 to "+" on the right side of the breadboard.

In g7 (next to the resistor) on the breadboard I have a jumper wire that goes from the "red" lead to pin 9 on the digital side of the Arduino Uno. For green (g9), the jumper wire goes to pin 9. For blue (g10), the jumper wire goes to pin 10.

Finally, on the top of the breadboard, I have a red jumper wire that goes from + to the 5V pin on the Arduino Uno and a black jumper wire that goes from - to the GRD pin on the power side of the Arduino Uno.

Will this wiring work?

2. There are two devices that I am trying to connect to my Arduino Uno; an RGB LED clear common cathode a color detector sensor. But I only have one 5V pin on my Arduino Uno. How can I provide power to both devices if they both need the 5V pin?

3. Can you recommend any example sketches that I can use to test my RGB LED? I want to make sure the LED is actually working.

Thank you!

proscience - The first thing I would do is test your LED and attached limiting resistors. You said that the LED is a common cathode configuration, so pin 8 is ground. If you attach a +5 volt source to the other pins, the anode connections, you should get the individual LED segments to light. My thought is that you may have a polarity issue in the connection of the breadboard. Keep it simple at this point. If the LED lights with this first test, check your breadboard with a voltmeter to assure that the connections to the LED pins is a +5 volts. Perhaps some attachment issues of the power supply to the breadboard is a source of problem.

Rick Marz

Hi,
Just a quick comment, you said:

For the ground lead on the LED, I have jumper that goes from Row 8 to "+" on the right side of the breadboard.

.

The ground lead should go to ground, which is usually "-", not "+". Try what Rick suggested first - connect the ground pin to ground (or "-") and the resistor directly to +5 and make sure that each LED color lights. Also, you need to know what voltage the Arduino is using to control the LED. Is the output going to +5 when it's supposed to be lit? Or is it going to ground? This will make a difference in how you wire the LED. Another point is to check the internal resistance of the AVR chip on the Arduino board, but that's secondary at this point until you figure out the other issues.

Keith