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Author Topic: Need help: 2 TLC5940 Arduino problem  (Read 1402 times)
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Hi all,

I got this project that uses the Arduino Diecimila to random fade in/out of 32 LEDs powered by 2 TLC5940. I did my connection based on this link.
http://tlc5940arduino.googlecode.com/svn/wiki/images/breadboard-arduino-tlc5940.png

I powered my 32 LEDs on a standalone 4 AA batteries and it worked a lot of times without fail.
However, this afternoon, i tested the TLC5940 library examples again and all the LEDs suddenly just doesn't light out (sometimes, it flickers but 5% of the time). I uploaded many times to arduino but to no avail. I checked the connection diagram, hoping I didn't screw up. But the connections were correct.

Still, I realized only when I press my finger around pin 19-21 of the first TLC5940, the 32 LEDs suddenly light up, just the way it should be.

Could anyone help me on this one? I've seen some posts on the TLC 5940 problem on putting ceramic capacitors but I doubt since it worked before.
I'm not sure if there's possibilty i burned the TLC chips D:
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It's hard to say without seeing your setup.  Take a pic and post it.  If you don't have decoupling caps, that could be your problem (which I think it is).
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Sounds exactly like you have a Vcc and GND connection swapped. 
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Sounds exactly like you have a Vcc and GND connection swapped. 

Based on what?
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22 is Gnd, 21 is VCC - could just be a poor connection to one or the other.
19 is DPCRG, usually that is static, either hi or lo.
20 is IREF, usually a resistor to Gnd.

Check out your connections.
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Thanks for the swift reply guys!

Here's a video concerning the problem.
http://www.youtube.com/watch?v=CTO_Zrh05m0&feature=youtu.be

It seems Now the moment i touched the Arduino's edge, the 32 LEDs doesn't even light up for no apparent reason. Somehow I suspect the chips maybe damaged due to ESD as my circuit had worked a couple of times without capacitors..



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« Last Edit: April 11, 2013, 11:52:53 am by Kup0 » Logged

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Still, I realized only when I press my finger around pin 19-21 of the first TLC5940, the 32 LEDs suddenly light up, just the way it should be.

"around pin 19-21" is a bit vague.

Can you be any more specific? Touch individual pins, etc.

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22 is Gnd, 21 is VCC - could just be a poor connection to one or the other.
19 is DPCRG, usually that is static, either hi or lo.
20 is IREF, usually a resistor to Gnd.

Check out your connections.

 i triple-checked the connections, it is correct. I even re-did the connection on a different breadboard just to make sure..but alas..
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Here's another video of the serious TLC5940 problem.

http://www.youtube.com/watch?v=16EUaghGOkw&feature=youtu.be
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I'm gonna say "capacitors, add some"...
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I'm gonna say "capacitors, add some"...


Alright, I gotta try tomorrow to see if that's the problem. So is needed to do is to put two ceramic capacitors onto the two IC chips based on this thread?

http://arduino.cc/forum/index.php?PHPSESSID=2ad6483bc4f6fa78406acd64a2406621&topic=134953.0
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Alright, I gotta try tomorrow to see if that's the problem. So is needed to do is to put two ceramic capacitors onto the two IC chips based on this thread?

Yes.

I'd put some near the LED anodes, too. Maybe three. Connect them between +5V and GND as close to the LEDs as possible.
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I recently had a similar accident (slipped with a oscilloscope) and had all light lit an nothing else.
I left it for a few days the redid the wiring. and it looks to be working again.
Im using breadboard and suffered a combination of shorts and loose connection.
Not understanding modern tronics I assume I tripped an internal fuse and had to re set it.
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Hey guys, I'm embarrassed to say that I actually found out the problem... I connected the pin3 wrongly. Now it works flawlessly.
I did connect the capacitors. Works fine as well.
Thanks Fungus
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Operator error, the usual suspect!
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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