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Topic: TLC5940Mux - How do I wire it up? (Read 2218 times) previous topic - next topic


I was wondering if I could play a little bit with the TLC5940Mux but I am unsure about how to wire the setup up and what exact parts I have to buy.

I've drawn the wiring in the attachment as far as I understood it. But I do not know how to insert the PNP Darlingtons... Can someone please draw an example for me?

And does anyone know if I could use these Transistors because I did not find the ones recommended in the example files? http://www.reichelt.de/BC-Transistoren/BC-516/index.html?;ACTION=3;LA=2;ARTICLE=5001;GROUPID=2881;artnr=BC+516

And is there a big difference between 74LS138 and 74HC138?? As far as I understood I could use both for this thing, right?

Thank you!


What are the PNPs for?
I believe the 74xx138s have 1 of 8 outputs low. The '5940 sinks current, so it will be turning on 7 of the 8 outputs all the time.

Neither one can source very much current (look at Voh and the current Ioh) while the '5940 can can a sink a lot more current.

Did you perhaps mean put an inverter between the '138 the LED Anode so that only 1 is active and being PWM'd byt the '5940 at a time?
Or is that where the PNP transistor comes in? The 1 low turns on a PNP to let current flow into the LED anode for '5940 to sink?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Check our the library for it, it has wiring examples: http://code.google.com/p/tlc5940arduino/


Thank you for helping!
Here is what the text in the example file says:
    Analog 0-2 (PORTC) is hooked to a 3:8 line decoder (74LS138) which pull the
    Base of a PNP darlington (MPSA63) low through a 10k resistor for each row.
    +5V is connected to the Emitter of the PNP's, and all the anodes (+) of the
    leds for each row are connected to the Collector.
    Currently I'm trying to fix timing issues by putting some D-type positive
    edge triggered latches between PORTC and the 3:8 line decoder, clocked on
    the rising edge of XLAT, but this doesn't seem to help.  I'm bringing the
    circuit in to the logic analyzer this weekend to see exactly when the ISR
    runs and how long it takes to shift in the GS data.
    Alex Leone, 2009-04-30

But I have to admit, that I am not very familiar with the transistor stuff...

The link provided by KirAsh4 only shows a wiring example for the standard use, not for the multiplexed setup...


This project:-
Shows a TLC5940 being multiplexed but I used my own library (included in the files), as a 4 x 4 RGB matrix.

This project shows an 8 x 8 RGB matrix
Again my own library.

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