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Topic: How many LEDs can I fade using UNO? (Read 6418 times) previous topic - next topic


Btw, if I go with this diagram, I´ll still need resistors for each individual diod, right?

Tom Carpenter

Nope, you only need one as shown in that diagram.
The TLC5940 outputs have a built in constant current source. There is a single resistor connected to IREF (pin 20) which sets the current for all output.

For the TLC5940
Iout = 39.06/Rref

That diagram shows a 2k resistor being used for Rref, so that gives:
Iout = 39.06/2000 = 19.5mA for each pin, which is pretty standard for an LED.


Oh, great... What about that fading SIN wire at the top of the diagram? Is that for additional TLC5940s or something?


SIN is where the serial data goes in to the chip (pin 26).
If you want to use more than one chip then the SOUT (pin 17) would connect to the next chip in line on it's SIN pin.

SIN PIN  :smiley-eek:

I'm allowed to have it 'cos it's not sharp.

Tom Carpenter

I believe that is the Serial out pin of the top TLC5940. It would connect to the Serial in pin of another one if you wanted to use more than two. Essentially they have built in shift registers and you are daisy chaining the shift registers of each IC.

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