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Author Topic: Probably making a stupid mistake, but need someone to point it out to me  (Read 1687 times)
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However, none of my blue lights turn on, only the red ones.
the only way to make any sense out of this whole thing is to take a single
Led in hand, and play with it until you get the pin connections straightened out.

Then, if I truly believed they had built-in Rs, I would take exactly one Led with the
intent that I might be sacrificing it to the gods of thermodynamics, and apply full
voltage to it, and see if it glowed for an instant and then forever flamed out.

ONLY THEN would I hook up the original ckt shown. Better than blowing up $18 worth
of Leds at square one.

Yeah, I did all that. That's how I know that the LED works at full current on 3.3v, at least the 3.3 volts supplied by my Teensy3. That's also how I know I've for sure got the wiring right for this particular model of LED. I know that I am not going to blow these out at this voltage, and my question is why the blue lights aren't turning on when the red ones are on, not whether or not I'm about to blow up 20 bucks of hardware. I'm not.

However, thank you for the recommendation for the three grounds and resistor on Adafruit. I'll be making a better board today and implement protection and such so that when I'm running it at high voltages they don't burn out.

Looking forward to the OP's schematic being posted on this one.

Oh boy... I'm not very good at schematics, but I'll try. Give me a bit.
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Oh boy... I'm not very good at schematics, but I'll try.
Make them look like you see the pros do. Have the positive lines at the top, the ground at the bottom and signal flow if any from left to right.
Have a look at some of the schematics on my site.
http://www.thebox.myzen.co.uk/Hardware/MIDI_Footsteps.html
and others, linked at the top of the page.
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the land of sun+snow
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That's also how I know I've for sure got the wiring right for this particular model of LED.
......... and my question is why the blue lights aren't turning on when the red ones are on,
The 2nd half of this comment indicates the 1st half is not entirely accurate. All in all,
electronics really is magic, but hooking up Leds is not.
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Um, I must respectfully disagree. I know which pin is the common anode, and which ones are the ground for each respective color. What other information should I know about this? The lights work fine on separately, and when all are set to one specific color, and I can flash one between blue and red and green no problem in quick succession. Is there something I am missing here? Because I don't see how this is relevant when we established much earlier in the thread that my issue is probably due to a lack of current control or lack of forward voltage bias separation between the LED's that I have. Sorry if I'm coming across as rude, I'm just genuinely confused.
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Um, I must respectfully disagree. I know which pin is the common anode, and which ones are the ground for each respective color. What other information should I know about this? The lights work fine on separately, and when all are set to one specific color, and I can flash one between blue and red and green no problem in quick succession. Is there something I am missing here? Because I don't see how this is relevant when we established much earlier in the thread that my issue is probably due to a lack of current control or lack of forward voltage bias separation between the LED's that I have. Sorry if I'm coming across as rude, I'm just genuinely confused.

Did you ever measure the voltage at the LEDs?  I really suspect that the device driving the LEDs (Arduino pin) was doing the current limiting for you and dropping the voltage down to the Vf of the red LEDs when one or more of them was on.  As soon as they were all off, the output voltage would rise to the Vf of the blue LEDs.  I don't know about the mega specifically (since I haven't looked into it yet), but many microcontrollers have approx 100 ohms of output impedance.  This automatically limits the current to 50mA max.
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Experience, it's what you get when you were expecting something else.

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I'm just genuinely confused.
And so are we. What you report is not possible so there is something wrong that you are not telling us. We have had some guesses and you say it is not that so we are waiting for your schematic to throw some light on the situation.
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Yep, I'm just at work at the moment so once I get home I'll be making a schematic. Any particular recommendations for a software package to do that with? Otherwise I'll go with ExpressSCH.
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My very first test with these pancake RGB LEDs was with a multimeter on diode/continuity mode.  I use that to test LEDs a lot, since it's high enough voltage to light one up, but is current-limited enough that it's not particularly bright.

So, with one of these LEDs in hand, I tested all the pin combinations (my data sheet was a little more helpful, but not much) to find the one pin that seemed to be the constant required to illuminate all of the colors.  Great.  So, then, I tried shorting the R and G pins to make yellow.  Nope.  The R and B pins to make purple.  Nope.  The B and G pins to make cyan.  Nope.  If I set the tip of my probe on one color and rocked it over to touch another, the first would be lit up until I touched the second, which would stay lit until I rocked the other way, then the first would come back on.

I think Grumpy is on to something here.  I bet what is happening is that the lower forward voltage diode is pulling the supply down enough that the higher forward LEDs are no longer lit.  Isolating each internal diode with current limiting resistors would probably fix that . . .  Huh, glad I stopped by this thread.
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Any particular recommendations for a software package to do that with?
It is called pencil and paper, photograph the results and post.
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the land of sun+snow
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thank you for the recommendation for the three grounds and resistor on Adafruit.
Three things. First, you need 3 separate resistors, one in each Led cathode line, in
case you're not doing that.

Secondly, if you check the datasheet [which is one of the worst I've seen yet - they
show no schematic and 2 A's and 2 C's, rather than 1 A and 3 C's like adafruit says],
you'll see the d/s mentions needing 3.8V to turn on the green Led, so it won't light if
you have only 3.3V.

Thirdly, the d/s says 3.8V for green, but it's usually the blue that takes the most voltage
to turn on.
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