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Topic: Question about capacitors (Read 3544 times) previous topic - next topic

Grumpy_Mike

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Btw what is the purpose of the resistor in the signal path?
To stop you frying the first LED in the strip if the strip's supply voltage drops lower than the driving signal and to prevent reflections on the line between strip and Arduino causing excess voltage spikes.


jendalinda

To stop you frying the first LED in the strip if the strip's supply voltage drops lower than the driving signal and to prevent reflections on the line between strip and Arduino causing excess voltage spikes.

Would be an internal resistance of a 74LS buffer sufficient? I'm going to use it as a converter from a 3.3V logic.

Grumpy_Mike

#17
May 14, 2018, 02:36 pm Last Edit: May 14, 2018, 02:38 pm by Grumpy_Mike
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Would be an internal resistance of a 74LS buffer sufficient?
And what stops the 74LS buffer from frying? Look a resistor is only $0.01 what is the big deal?

Now I am on my laptop I can show you the signals with and without the resistors.


jendalinda

And what stops the 74LS buffer from frying? Look a resistor is only $0.01 what is the big deal?

Now I am on my laptop I can show you the signals with and without the resistors.


Thanks for the explanation. Is there any difference if the resistor is at the MCU or at the LED?

Grumpy_Mike

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Is there any difference if the resistor is at the MCU or at the LED?
Not a lot but it is slightly better at the MCU end.

drcak

Would you say such capacitor is beneficial if I use a power supply like this one?
https://www.meanwell.com/Upload/PDF/LRS-100/LRS-100-SPEC.PDF


After you turn it off, the status led on it lights for quite a while before going dark, so I would say it has a capacitor somewhere at the end. Or this isn't that simple?

Grumpy_Mike

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Would you say such capacitor is beneficial if I use a power supply like this one?
Yes.

Meanwell are known for their crappy designs. But anyway a capicator where the current is drawn is far better than having it way back in the power supply. Yes an LED stays on a long time but so what? It says nothing about the ESR ( effective serial resistance ) of the capacitor, and that is much more important than mere capacity and charge storage, if you want to suppress transients which is the whole point of using one.

drcak

#22
May 17, 2019, 11:01 pm Last Edit: May 17, 2019, 11:04 pm by drcak
Thanks!
Could you recommend a brand with not crappy designs?

Can I measure with a multimeter whether this capacitor is required?

Also,
To stop you frying the first LED in the strip if the strip's supply voltage drops lower than the driving signal and to prevent reflections on the line between strip and Arduino causing excess voltage spikes.
If I fried the first LED, would that result in a break on the strip's 5V line at the first LED?

Grumpy_Mike

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Could you recommend a brand with not crappy designs?
Not as such, but avoid eBay and use a respectable distributor like Farnell, DigiKey or Mouser. You pay more but get quality stuff.

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Can I measure with a multimeter whether this capacitor is required?
No.

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If I fried the first LED, would that result in a break on the strip's 5V line at the first LED?
No.

drcak

Thanks! Do you maybe have any idea what could cause such damage? It was working fine for a while and when I tried to plug it in again, this is what I realized.

Grumpy_Mike

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It was working fine for a while and when I tried to plug it in again, this is what I realized
Lots of damage is cumulative, yes it might work for a time with things chipping away before it actually fails. It could be many things. For example if you apply a signal to the strip before you apply the power to it.

Power supply bring up is important, if you connect and power up your Arduino and then power up the LED strip, you have a signal going into the strip but no power to it. That can damage things, the series resistor in the data line is designed to offer some protection if that happens.

drcak

This should 'break' the data line, not the 5V though, right?

Grumpy_Mike

Yes, you can't break the 5V line as it does not go through the chip, it is just a piece of copper wire.

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