Rainbowduino : Max light power on 20mA RGB LED


How can I get the max light power from my RGB led. If I use the demo prog. the max Iout is ~ 1.5 mA (read by multimeter) !!!
How can I get 20mA ?



What value of current limiting resistor are you using, what’s the forward voltage of your LED and your power supply voltage?

Either the limiting resistor is too large, or if you’re driving the LED from a microcontroller, it may be that the LED is being driven by a PWM signal.

Hi, I use a Rainbowduino the current is limited by the MBI5168, I set the Rext @ 1kOhm -> 20mA. The LEDs are driven by PWM… But when the output of the Rainnbowduino is set @ 15 the max Iout is ~ 1.5mA
If I set the Rext @ min (<100Ohm) I get only 10mA :confused:

Ah okay, I missed that it was the Rainbowduino. I’m afraid I’m not familiar with it, but can you scope the PWM output to the LED to ensure the duty cycle is as high as possible? If the Rainbowduino needs to multiplex the outputs, you’ll see a reduced average current on a single LED if it’s only on for an eighth (or whatever) of the time.

OK… with Rainbowduino you can’t drive @ max power a 20mA RGB LED !? Because, if you set the max Iout 120mA / 8 = 15 mA max !!! Is right ? :frowning:

I don’t know, that’s just a guess! As I said, I’m not familiar with it. Depending on how many LEDs you want to light you could change the software to just have them on.

To work it out, you could either work your way through the demo code which I think seeed has online, or you could scope up the outputs to watch what’s going on.

Hi Tops, did you try increasing the power supply voltage (VCC)? At 5V the LEDs are pretty dim, it works better at 7V+. The LEDs are still multiplexed by rows using the default firmware, so they will not be driven to the max possible power. If you only have a few LEDs to drive (up to 24 or 8xRGB) look on the Seedstudio blog for the large seven segment display demo program which doesn’t multiplex.