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Author Topic: So many possibilities to troubleshoot... Where do I begin?  (Read 1854 times)
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I would use 1 per.
If you use a surface mount ceramic these are easy to solder under the I.C.


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The way you have it in your schematic isn't the same as how you have it wired up! That goes for me too.

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Would placing them like this be good?



* Screen Shot 2014-02-04 at 11.45.42 PM.png (37.05 KB, 895x697 - viewed 22 times.)
« Last Edit: February 04, 2014, 11:37:31 pm by Loren » Logged

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Great.
You could thicken the longer trace.
« Last Edit: February 04, 2014, 11:53:06 pm by LarryD » Logged

The way you have it in your schematic isn't the same as how you have it wired up! That goes for me too.

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So I've made several more adjustments to this project.  Attached is the latest schematic.  

Check the wiring of the shift registers. Either the schematic is wrong, or you have connected them wrong.
This is explanation and shows cascading for 2 shift registers:
http://bildr.org/2011/02/74hc595/
You have enough pins, so you don't need cascading.

Could I address each shift register individually?  If I can address each register individually are there any downsides to doing so other than using extra pins?




I'm going to be using LED strips.  I thought I saw current limiting resistors on the strip.  If they have them on the strip would it be necessary to include them on this board?


I did see that there are resisters on the LED strips.  Does anyone have a recomendation as to whether or not I should include current limiting resistors as part of this schematic?

Again many thanks everyone!

Loren


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« Last Edit: February 06, 2014, 09:26:22 am by Loren » Logged

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Shift registers:
Shift registers can be used in many ways, but is it useful ?
Pushing 24 bits into the shift registers is very fast. I think there is no need to change it.
But you could connect the latch to individual Arduino pins, and if you don't chain them, you can use one at a time. That would result in 5 pins on the Arduino, not a problem.
Updating all of them will not be faster. You can seperate the serial data, and use 7 pins on the Arduino. But the extra code in the sketch will still not make it faster.

Led strip resistors:
The led strip is for 12V. Often 3 leds in series are used, with a resistor, to make it work for 12V. With a led strip, you don't need extra resistors.

fade
To get all the RGB colors, a PWM signal is used for every 'R', 'G' and 'B'.
Since you use the shift registers, using PWM is a lot harder and not so smooth anymore. Did you know that ?

maximum current
I see you have the 12V at the led connector, and the ULN as driver.
The ULN chips have a maximum current per output and a total maximum current.
Can you check that ? The current depends on the length of the led strip.
« Last Edit: February 06, 2014, 11:57:46 am by Caltoa » Logged

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Maybe late to the game, but I would just use qty 3 TPIC6B595, in place of the HC595 and ULN2803. 150mA current sink per output, rated to 50V. 3 LEDs/strip are generally 20mA, so 21 LED strips would be supported.
There are other versions of TPIC6x595 that can sink more.
I have boards on hand already that have arduino functionality and 3 TPIC6B595s already made if you want to buy a bare board, or an assembled one.  Will post a pic  when I get home.  All thru hole, easy to assemble.
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Thanks to both of you for all of your input!

Shift registers:
Shift registers can be used in many ways, but is it useful ?
Pushing 24 bits into the shift registers is very fast. I think there is no need to change it.

I'll leave it as is then.  I think that I have a board with 4 shift registers that I can play with until I actually get this one made.

Led strip resistors:
The led strip is for 12V. Often 3 leds in series are used, with a resistor, to make it work for 12V. With a led strip, you don't need extra resistors.
This is also good news.
fade
To get all the RGB colors, a PWM signal is used for every 'R', 'G' and 'B'.
Since you use the shift registers, using PWM is a lot harder and not so smooth anymore. Did you know that ?
I had seen it eluded to but not specificly talked about.  I think for my application I might not need the fade part, but I'll do some testing and find out.
maximum current
I see you have the 12V at the led connector, and the ULN as driver.
The ULN chips have a maximum current per output and a total maximum current.
Can you check that ? The current depends on the length of the led strip.
The datasheet for the texas instruments chip located here:  http://www.ti.com/lit/ds/symlink/uln2803a.pdf
 mentions 500mA peak collector current.  Does that mean for the entire chip or per IO?

Maybe late to the game, but I would just use qty 3 TPIC6B595, in place of the HC595 and ULN2803. 150mA current sink per output, rated to 50V. 3 LEDs/strip are generally 20mA, so 21 LED strips would be supported.
There are other versions of TPIC6x595 that can sink more.
I have boards on hand already that have arduino functionality and 3 TPIC6B595s already made if you want to buy a bare board, or an assembled one.  Will post a pic  when I get home.  All thru hole, easy to assemble.

Nope not too late.  I'll do some looking and try a layout to see what I can come up with.
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I can't find the maximum current of the ground pin of the ULN2803. It is perhaps not in every datasheet.

If you can use the CrossRoads board with TPIC6B595, that is a very good option. Reducing the number of chips is always a big plus.

By the way, I did make a led pwm dimmer once with the leds behind a shift register. Since the shift register and the Arduino are both fast, it was possible. I think I used direct register writing and a timer and a software interrupt.
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I think that I have found a surface mount version that would work.  Check out the attached schematic for more details and let me know what you think.

As far as the pwm I was going to try something like this:  http://www.elcojacobs.com/shiftpwm/

Let me know what you guys think.

Loren


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Pin 7s are  floating, tie to +5 if not used.
Are you sure you don't want to use Q7 of I.C. 2?  Edit maybe you want "see image"


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« Last Edit: February 08, 2014, 11:50:09 pm by LarryD » Logged

The way you have it in your schematic isn't the same as how you have it wired up! That goes for me too.

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Ok, so for the next version.

Pin 7s are  floating, tie to +5 if not used.
Are you sure you don't want to use Q7 of I.C. 2?  Edit maybe you want "see image"
Thanks for the tips. 

Should I connect the pin 7s to digital pins for versatility or is it worth it to use the pins.  Right now I just have pulled them high with the VCC out of the pro mini.

Thanks again!

Loren


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If you have an free pin on the controller, route it to the outside of a three pin male header.
The other outside pin could be connected to +5V.
The middle pin of the header connects to pins #7.
Place a header jumper on the +5V or controller side as needed.
In the controller position, you can send a clear.

I'll bet you are getting comfortable with your schematic drawing program, that's the way you learn.


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You guys are brilliant!

If you have an free pin on the controller, route it to the outside of a three pin male header.
The other outside pin could be connected to +5V.
The middle pin of the header connects to pins #7.
Place a header jumper on the +5V or controller side as needed.
In the controller position, you can send a clear.

I'll bet you are getting comfortable with your schematic drawing program, that's the way you learn.

I'll incorporate that.
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