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Kermit

Member Since 30 Mar 2012
Offline Last Active May 24 2012 06:02 PM
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Posts I've Made

In Topic: TLC5940

14 May 2012 - 09:15 PM

Hi Mark (Nevyn? :-)). As usual, you are right, even to be convinced I had to read the datasheet three more times! :-) It's so strange that I'm used to software, but electronics is still so hard to grasp, for me! :-( Anyway, if the DC registers are random, it's so strange that in the current chip they are all at 100% minus one (at least for what I can say, looking the leds...) Other things to test... I will never see the end of this!!! :-))) Andrea P.S.: I could use this pwms to control three L293Ds with attached motors, and at least this part flowed really smooth! Motors go up and down without any problem!

In Topic: TLC5940

14 May 2012 - 03:31 PM

QUICK UPDATE: I changed the chip (I got 6 of them :-)), and all the outputs (minus one!) are uniform and smooth, so the code, for what I can see, is perfect. One output is kind of flickering, something like 10 20 times a second, but never going completely off, for what I see. The strange thing is that if I move the wires, in some position the flickering goes away. Can it be some sort of interference? Andrea

In Topic: TLC5940

14 May 2012 - 03:20 PM

Hi, Nzc, nice to hear from you again, thanks! No, of course I'm not looking for a power output, maybe I already said I'm to use the outputs to feed some L293Ds to control DC motors, so a few milliAmpere are more than enough. But on my side, if I feed (an external and stabilized) 5V I get erratic behaviour from the TLC5940, while with 3.3V (and coming from the Netduino!!!) it's all really perfect and smooth. Dot correction: in the datasheet it's said that to override it I have to give a more than 20VDC, and I'm pretty sure that I don't have such a supply! :-) So each time I turn on the chip, it should have just the factory set (1.0). In your code you don't set the values, so it should be all normal. ...I'm going on with my tests... A

In Topic: TLC5940

14 May 2012 - 02:19 PM

Ok, since I didn't give up, and made again all the steps suggested in this, as in other, thread, I finally found (I must have made something wrong on the first trial) what the problem really is: NEVYN was totally right, in the high level limit for the 5VDC used as Vcc. The datasheet is clear, even if I didn't pay too much attention on this: the high level limit is 0.8 * Vcc, so Netduino pins cannot drive the signal high (Nevyn says 0.7, but I think he hadn't the datasheet just in front). When powered by a 3.3 signal, all is smooth and good, under any condition, so I think this is the right solution to have. My only remaining problem is now that some of the pins are always off, some are partially powered, and so on. Now, there are two alternatives... one is that the source code I'm using (by NZC) still has some bug :-))) (no critics, here: you've done a wonderful work!) OR there is some dot correction on the chip (but this looks a little improbable... I never gave it the 20more VCC to write it! Some other test will solve (I hope) the situation! :-) I'll prepare a Fritzing commented diagram for the solution... Andrea

In Topic: TLC5940

12 May 2012 - 10:08 PM

No, it's really stranger than what I said: if I use directly led+resistor, all is smooth and soft... when using the TLC5940 all changes... :-((( Mario was right, when he said that this is a very strange chip... :-((( I don't know what to do: I changed the breadboard, the wires, and the netduino is perfect, using for example a motor with an L293D, but when I use the TLC, I have to touch the wires, and not always it behaves well... :-( I have three of them, and all show this behaviour! Bewitched chip... I'm sure... :-) Andrea

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