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Author Topic: Problem when expanding on the ShifOut tutorial for LEDs  (Read 7906 times)
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Decoupling term was used refering to the purpose they are fulfilling on the circuit. The components are capacitors. The ones you bought should do alright.
Ill remind you Nick's reference to Grumpy Mike tutorial about what are their purpose. Will be better than us explaining it ( you should get used to research for yourself, and ask for help with doubts as opposed to expect people to give u a-build-by-connecting-the-dots kind of tutorial. That way you will not only be independent, void crap directions and also give you a much more complete insight into WHY things work as they do, and are built as they are !




Read Grumpy Mike's tutorial about them:

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

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2. It looks like he just placed them randomly between the + and - rails.

I placed them along the rails yes. I put one on each side, near to the chip, so basically as close as I could to the Gnd and +5V for each chip, on each side. Extra ones aren't going to hurt, and they will help dampen down the noise that would move from one chip to the next, possibly corrupting the data it is receiving.

Probably ideally they should be very near the Vcc pin of each chip, and run the other side to Gnd as closely as possible.
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Got it. Now I need to find the least tedious method for wiring 88 LEDs along a 4ft bar :/ I tried soldering the ground leads to a flat steel steel bar but the solder wouldn't stick.
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When I need to do something like that I use 1/4" strips of PC Board (.032") thick. I used to have a sheet metal brake at my 'disposal'. I mainly used them for common connections on prototypes of all kinds.

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I have gone through the incredibly, incredibly, incredibly, incredibly tedious work of soldering and wiring all 88 LEDs by hand across a 4ft span. All have been tested. I have a few issues that are out of my expertise.

In all of the following scenarios, I have to have the 5V wire going from the arduino to the breadboard removed or it won't work at all.
If I have caps in place, I get no response (from COM commands).
Without caps, I get response but really noisy and unusable.
If I put one cap only at the + - rails next to the first chip AND I put a LED w/resistor right next to it, It works almost 100% correctly. (The command to turn all of the LEDs on needs to be sent twice because the 11th chip doesn't light up until the 2nd time). Get this, if I remove the LED w. resistor from the equation, the whole thing doesn't work again.
Can you explain wtf might be going on?


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Is this problem just way too difficult to solve or am I not explaining a specific part of it correctly?
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What 5V jumper? You've lost me there. There should be 5 wires going from the Arduino to the breadboard, as pictured above.

If I unplug the 5v jumper on the arduino, the LEDs light up and flash/blink. If it's plugged in, nothing works.

You've said this about 5 times now and I just don't understand you. What jumper? Can you explain in great detail about it?

For me, saying "if I unplug the 5V wire it works" is like saying "if I unplug my TV from the power point it works".

It doesn't make sense, so there must be something I am missing here.

Did you install the decoupling capacitors? How many? Where did you put them?
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The wire going from "5v" on the arduino to the positive rail of the bread board.

I put the caps along the + and - rails just as you did.
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OK so what is powering the LEDs?
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must be the juice coming from pins 10/11/13. I've tried so many variations. Only the scenario I described a few posts ago works. It still has noise issues but more caps make it unresponsive. There's always one, specific LED the lingers ON most of the time. clearing it only clears it for a short while.
« Last Edit: May 06, 2012, 07:54:42 pm by David82 » Logged

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If you are not supplying +5V to the Vcc of the shift registers there is something seriously, seriously wrong. Solve that first.
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It's getting the 5v it needs from pins 10/11/13. It does work. Just has a tiny bit of noise issues and only works under a bizarre configuration as described earlier. In the diagram on your site there is a 10k resistor going from SS <D10> to ground.
1. What's that for and is it really needed? Could it help with the noise?

2. I noticed all of you caps are set diagonally. Is there reason behind that?

3. My caps looks different too. They are the brown (ceramic disc). Does that matter?
« Last Edit: May 06, 2012, 08:43:35 pm by David82 » Logged

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He might be right, Nick, if it was just a few leds. If it aint many, ive seen the mux'ers pass enough to light them... But what it is strange is the fact that he is talking about 80 plus leds ?!?!?  lol That TV analogy exactly what id used.
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It's getting the 5v it needs from pins 10/11/13. It does work.
No it is not.

This is called paricitic powering and is a good way to destroy chips. Unless you connect all the chips to the 5V line you don't stand a hope in hell of getting anything working. Chips are made to take power from their 5V input and ground.
As you try and scale up you get two problems, first you get noise on the supply lines that distributing decoupling capacitors can help with. Second the signals that go to all the chips, like the clock signal, are not strong enough to power all the chips. Using two inverting buffers back to back will give you one non inverting buffer. You should use the buffer output to drive no more than 10 chips.
Finally make sure your power supply can handle the current for all those LEDs.

Remember you are asking for help, however you seem to be rejecting most of it. Think about it, is that a smart move?
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It's getting the 5v it needs from pins 10/11/13. It does work. Just has a tiny bit of noise issues and only works under a bizarre configuration as described earlier.

You have a fault in that case. You need to rectify it. The fact that power is somehow working its way into the logic lines and powering the chips would account for any number of problems.


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In the diagram on your site there is a 10k resistor going from SS <D10> to ground.
1. What's that for and is it really needed? Could it help with the noise?

It's to keep SS low during the Arduino power-up sequence (it should probably be a pull-up but whatever). Its sole purpose is to stop some random pattern appearing before the first sequence is sent out by the processor.


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2. I noticed all of you caps are set diagonally. Is there reason behind that?

Purely because of how far apart the leads were.

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3. My caps looks different too. They are the brown (ceramic disc). Does that matter?

No, the type of cap shouldn't matter.
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