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Topic: TLC5940 with Common Cathode (Read 3 times) previous topic - next topic

marian42

Hi,

I want to build an 4³ LED cube that is controlled by a TLC5940 (and an Arduino Uno).

I just assembled this circuit to test the IC:


I already soldered the LEDs together and all cathodes of a layer a connected to turn on and off the layer.
So the anodes of the LEDs will be connected to the IC.

In the example the cathodes are connected to the IC and the anodes go to 5V.
My idea was to connect the LEDs vice versa between GND and the TLC5940 and invert the values.
However, as soon as I disconnect an LED (or connect it vice versa) there is no more voltage at the ouput pins.

Is it possible to run my LED cube with the TLC5940?

fungus


I already soldered the LEDs together and all cathodes of a layer a connected to turn on and off the layer.
So the anodes of the LEDs will be connected to the IC.

In the example the cathodes are connected to the IC and the anodes go to 5V.


The example is correct, the cathodes should go to the TLC5940.

The anodes are connected together in each layer, not the cathodes. Time to start again...

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

BulletMagnet83

Probably best not to solder things until you're sure it works... and do as the example does :) Made the same cock-up myself before, so don't feel too bad!

marian42

Im sure that it works!

I followed a tutorial that instructed me to do like this.
http://www.instructables.com/id/The-4x4x4-LED-cube-Arduino/step4/Construct-the-cube/

I definitely know that it is possible to use this setup but control it with something else than the TLC5940.
The Arduino outputs LOW to the Layers and the LEDs that light up get HIGH from their other pin (connected to the IC).
This would work with a 7HC595 (or two of them) what I intended to do first. But this solution is not able to do PWM (or not fast enough).

The problem I have is that the voltage drops if I disconnect the LED.

MarkT

The TLC5940 _cannot_ drive common cathode LEDs, it is a current sink driver.  The 74HC595 has push-pull outputs so can source or sink.
[ I won't respond to messages, use the forum please ]

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