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1  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 29, 2014, 12:50:35 pm
Indeed. BAD Willy!  smiley-sad-blue

I fixed it, now I'm using just one led, 40ohms resistor, 5V supply, ULN2803. It works correctly. 23mA on the led and it looks good. ;-)
2  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 29, 2014, 07:47:52 am
Ok, I got a fancy multimeter so I can test things correctly. But them I got confused again. Here's what happens.

I got 3 ultra bright straw hat leds, rated 3.2 to 3.4, connected in series, with the (-) to the ULN2803, and the (+) to the 12V power.
I'm using the ULN2803 to drive them with a 12V power adapter rated 1A. It reads 11.5V on the output when connected to my Arduino board (the VIN connection).
When I connect a potentiometer to test the leds from the ULN2803 output, and check the mA usage, I can only go as high as 63mA for the 3 leds when the potentiometer is at zero ohms. If I remove it and just connect directly without a resistor, the same result, max of 63mA, and it fluctuates a bit. No heat, no led explosions. ;-)
The voltage output of the ULN2803 pin is 0.8V, a bit low I guess. The chip reads ULN2803APG Toshiba, in case it is important.

So I wonder if I got something faulty here or if I'm doing something stupid. <shame face>

Maybe I will test with a 2N2222 Transistor instead, to get better values...

Please, advise? Thanks again guys!

Best Regards, WilliamK
3  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 08:20:51 pm
You would use the voltage across the "gate" output, which is an open collector output (each) of a Darlington transistor.
That could be around 1.5 to 2 volts

Ifyou run 150mA down an output then figure 1.5V * 0.15A = 0.225 W

Oh, thanks!! But do you mind telling me how can I measure that?

If I lower the channel needs down to 100 mA I will be using less than 2w in all ch...
4  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 07:57:16 pm
P(W)= V (V)* I (A)

Yeah, indeed, I'm aware of that. ;-) but what voltage I use? The Led Vf, system V, what?

Thanks again.
5  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 07:04:20 pm
check page 6 of the specs which shows tables for max duty cycle at specific current level with number of devices running.
For example if you have 7 channels at 200ma per channel you can run 100% duty cycle.
Or say for 8 channels you get 50% duty cycle at 300ma
So setup one channel and measure the current draw if you run 6 channels then look at your current draw interset with 6 channels and see how much duty cycle you can run.
In reverse if you want 100% on time then for 6 channels limit your out puts to about 220ma per.

Thanks, I understand that, but still don't known how to calculate the watts value to see if it will be under 2watts total, for 16 x 150mA 3.3V Leds in a 12V system...
6  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 07:01:00 pm
I'm starting to think it will be easier to just use a 200mA transistor (npn?) per channel? Again, it will be 16 sets of 4 or 6 leds, around 150mA Max each of the 16 sets... still need to understand about the power disipation watts thing...
7  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 06:43:20 pm
So, I use the Led Vf (3.2V) or the system 12V, multiply with all channels mA or what? Thanks again, and sorry for the silly questions. ;-)
8  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 06:32:14 pm
One question, how's the math to check the Wattage when running several leds? The input will be 12v, with the right resistor to get 22 or 24mA... as I read that the uln has power disipation problems over 1.5 watts...
9  Using Arduino / Project Guidance / Re: BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 06:28:32 pm
Thanks, those datasheet are complete, the one I had wasn't... ok, so it does support 150mA for all 8 channels, nice!! I will work with that in mind. :-)

So far the idea is simple, 16 led squares, each with 4 or 6 leds. Tomorrow I will do the math and decide on things...

Cheers!
10  Using Arduino / Project Guidance / BIG Led Matrix with ULN2803A at 12V on: September 25, 2014, 02:50:24 pm
Guys, it has been a long time... ;-)

I'm currently doing some research on how to build a big 4 x 4 LED Matrix, but using 16 Arduino Pins and two ULN2803A ICs.

I'm using 12V for the ULN2803A so I can drive 3 leds in series with a 56ohm resistor. The leds are super bright white leds, with a Vf of 3.2 so I'm worried that this may break the ULN2803 when we have all 8 channels on.

6 leds per channel = 150mA * 8 channels = 1.2A @ 12V

Is this possible? I have only tested one channel so far, and it works correctly. My main worry is when all channels (96 leds total) are fully on. I don't mind if they dim a bit, just worried about heat and blowing up the ULN2803... ;-)

Another solution, I guess, would to use one transistor per channel and forget the ULN2803...

I'm also considering just using 4 leds per channel and running at either 12 or 9V, using 2 x 2 leds in series. I would them get around 100mA total per channel.

Any advice is much appreciated!

Best Regards, Guilherme (William) Kalfelz
11  Using Arduino / Audio / Beat707 Pulse - Dual ATmega328 project with "Analog" styled waveforms on: February 09, 2014, 07:31:47 am
Announcing the Beat707 Pulse synth project created by Jack, our new contributor. This is based on the previous Beat707 SY LE project, but with some twists. This is a WORK in progress, as Jack wishes to see how many users will jump on board. We are gathering some money in order to pay Jack's time, so any contribution will be welcome. For that, we decided to make the project paid-for. You can still get schematics and source-code, for a Do It Yourself (DIY) project.

Please, visit the following link for details on this project, including videos, mp3 and other links...

http://www.beat707.com/w/updates/116-beat707-pulse





-----------

And you can hear some examples in this MP3:

http://www.beat707.com/downloads/Beat707_SY_LE/Beat707_SY_LE.mp3

And here's the new about Jack, our new contributor. :cool:

http://www.beat707.com/w/updates/115-you-dont-know-jack
12  Using Arduino / Audio / Re: Using timer1 and 2 for great PCM Drums (6 voices) on: April 03, 2013, 08:52:02 am
Actually, this whole project is now on http://beat707.com/ and its called BeatVox, and has a GitHub url now.

https://github.com/Beat707/

https://github.com/Beat707/BeatVox
13  Using Arduino / Audio / Re: Using timer1 and 2 for great PCM Drums (6 voices) on: April 03, 2013, 08:49:14 am
Oh, very nice, thank you!  smiley-cool
14  Community / Exhibition / Gallery / Re: Big Clock LCD Display (with extras) on: March 01, 2013, 11:10:31 am
I just updated the code above, fixed a few bugs, improved a few things.
15  Community / Exhibition / Gallery / Re: Big Clock LCD Display (with extras) on: February 26, 2013, 08:43:32 am
Attached is the code. (2 files)
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