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Topic: 6x TLC5940 32 rgb leds (Read 16914 times) previous topic - next topic


Ok, thats what I was kinda thinking. I'm going to test the boards indiviually and then rebuild it all but this time soldering all the wires in the permanent box i'm building for it.


Well I soldered everything together and it all worked. I tried to do some color blending but noticed some of the led were not getting full brightness as they should so I re-soldered the anodes to the 12v rail instead of the 5v and they are at full brightness now which is good but it goes back to shifting as my previous problem. I want to add buffers to the signal lines but not sure what to buy or how to hook them up.

Do I hookup the signal line to the buffer chip and then connect the 6 tlc signal lines to that  single output  (I'm guessing this is the way), or does the signal line split to 6 buffer chips, one for each tlc? Or is there a buffer chip that has a single input to many  buffered outputs?

I have a decoupling capacitors on each tlc, I think they are .1nano (say 104 on them). Should I add some larger ones as well to each board? I'm thinking with the higher current it may be outputting more noise than the small caps can filter.



I think they are .1nano (say 104 on them)

No they are not.
They are 100000 pF or 0.1uF. The way you read it is 10 followed by 4 zeros.

Do I hookup the signal line to the buffer chip

What buffer chip is this?


I guess that was a general question about buffer chips as i'm not sure what to order.


You need a high side switch or current source buffer like the BTS6143 or the 2981.
You should have a pull up resistor from the TLC output to the +ve. Then connect your buffer input to the TLC output.
However then you no longer have a constant current output and need to do something else to limit the current.


I was referring to buffer the signal lines since they are getting split to 6 tlc's, not the outputs.


In that case a 74HC04 will act as an inverting buffer, two in series will give you a non inverting buffer. As you get 6 in a chip this will buffer 3 signals.
Alternatively a 74LS07 is 6 non inverting buffers with an open collector output, that means a pull up resistor is needed.


Sweet, I've ordered a bunch of those. The regular knight rider code works ok but it still has a shifting problem if I try to power on 32 leds or more. I'm hoping that the buffer chips on the signal lines will help but also wanted to add bigger decoupling capacitors to filter out the lower frequencies that the .1uf caps can't filter out. I've got 10uf, 47uf, and 100uf caps, besides putting them on the power line of the tlc chip is there any other place I want to put them?


Keep the 0.1uFs in as well to handle the high frequency stuff. I would put the extra ones at the power at the end of the line, and maybe another in the middle.


Mike... I think that you have it... poor power wiring and lack of proper bypassing would well explain his issues. Sometimes the order in which things are powered up has a GREAT deal to do here...
Particularly if the chips are manufactured by different outfits. Back in the day there were always issues, about power supply sequencing. Some Chips will latch up IF they have 'hard' control inputs that are biased on before the Vcc connections for the chip come active. The issue seems to come from 'input protection diodes' biasing the IC substrate before the Vcc is valid. I do remember 'hacking' a display/memory board (Surplus) and it wouldn't work unless the inputs were connected... The Engineer? that did that design {Not ME}, forgot to connect the Board Vcc, (actually a missing trace on the pc board) the board was powered by it's I/O and one of the reasons that 24 megs of Static Ram sold on a big pc-board... for $20.00 in the late 80's was that it was 'unreliable'.

--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard


I put caps on all the boards and stress tested the system by eventually turning all the outputs on and it does not glitch (extremely bright though). It sure does get toasty hot on my heatsinks but normal operation should be fine. 

It does still glitch when I run a code to increase the power on each delay, hold at peak, then decrease and choose a different color so that gives it a pulsing effect, but instead half the leds turn on, the others glitch so I'm thinking there is still noise on a signal line somewhere.

I just had a quick question about the buffer chips that i'm about to put in. See my wonderful paint skills in the attached pic.


Go with number 2.
Note that the 74LS04 inverts the signal, so use another 74LS04 before the first one so that the signal is the right way round when it finally gets applied to the TLC chip.


Yup, I also plan on buffering the first Sin so it is not out of phase by a clock pulse, but the other Sin's should be fine tied to the Sout's of the other boards.


Buffer chips all hooked up and working.

I have written code to increment the power by 10, hold when it maxes out, then decrement by 10, choose a different color and repeat for 0-15 and 16-32. 

Here is the video of it http://youtu.be/XE208O-SGA8 I noticed that it is tripping the power supply but only on this particular program. I can turn on all the outputs and get white light out of it without any problems but it seems that when I have it fluctuating a lot it trips the circuit protection.

The power supply is out of my gaming computer,  currently I have the anodes (v2) hooked up to a 12v 20amp rail. I'm thinking a very large capacitor will fix this issue, my other thought would be to move it to the dual 12v line meant for the processor, maybe both.


After putting a bunch of different caps on the 12v rail the system runs fine now.

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