Setting TLC5940 Dot Correction

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm successfully fading between a rainbow of colors with RGB LED's on a TLC5940. My problem is that some colors such as yellow and orange are difficult to achieve because the blue and green lights are significantly brighter than the red channel.

I've overcome this to a certain extent by keeping blue/green values very low when mixed with red which makes some mixed colors look very dim in comparison to mixes that just contain blue/green.

I found that the chip supports dot correction which seems to be what I'm looking for.. the ability to increase the power to the red channels. Unfortunately the only thing I could find in documentation was a method for setting all channels to a certain value and even that was very confusing.

Could someone point me in the right direction towards dot correction or some other solution to help with my color mixes?

If it helps, I'm using translucent (not clear) LEDs so there's some diffusion. I also stacked a few layers of translucent plexi over my bread board.. it doesn't help with the color problem.

Thanks!!

2

Are you using the same size resistor for each color? Typically, a larger resister is used for the red leg, to increase the current, than is used for the green and blue legs.

3

Are you using the same size resistor for each color?

No the TLC5940 don't use resistors to limit the current of the LEDs they are driven by constant current set by a single resistor for the whole chip.

I never got the dot correction to work either. I think on reading the data sheet you need to provide the high eeprom programming voltage to write to it and I never had that in my hardware.