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Topic: TLC5940 LEDs in series. (Read 499 times) previous topic - next topic

Cue2

I have a single tlc5940 and plan to use 8 RGB Leds with it. 4 on their own channels and 4 in series on a single channel. Am I right in thinking this is OK to do and that I can use the same R(I ref) resistor with or without the LEDs in series?

Grumpy_Mike

Unless the RGB LEDs have seprate connections for each led, that is 6 connections per led, you can't put them in seriese.

Cue2

Thanks mike for your reply. The LEDS are common anode so you are right, it's a 4 pin LED that can only be connected in parallel. Can I place them in parallel with a resistor for each and just have no resistor to ground on Rref?

Grumpy_Mike

You always need a resistor on Rref.
By themselves LEDs won't shair so you need a small resistor to help them equalise the current, so yes one in each LED in parallel.

Cue2

So I thought about using SoftPWM with the TLC5940 library to try and control more LEDS from the unused arduino pins but it seems SoftPWM and the TLC5940 library do not play nice with eachother. Is there any way to use the additional arduino pins to control additional 20ma RGB LEDs or should I give up on that idea?

Grumpy_Mike

Why not just chain additional TLC5940s together if you want more LEDs?

Cue2

#6
Jun 20, 2013, 04:20 pm Last Edit: Jun 20, 2013, 04:22 pm by Cue2 Reason: 1
I was more just wondering if I could make use of the extra unused pins but more LEDs are not really a requirement, partially because of space constraints and the perfboard I'm using.

it seems that the SoftPWM and tlc5940 libraries both use timer2 so it was a no go. I actually gave it a shot anyway. Lets just say I'm fortunate to not have epilepsy because the results weren't what I was expecting.

Grumpy_Mike

Yes the two have great CPU demands. You will get a beating of the two signals that will not look good.

If you want more LEDs then you could look at an I2C PWM LED driver, just two pins and as many LEDs as you can shake a stick at.

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