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Topic: LEDs without the use of current limiting resistors (Read 6363 times) previous topic - next topic

Boffin1

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Because both statements ("you have to use a resistor" and "you cannot use resistors") are wrong. Whether you should use a resistor or not is application specific and needs to be evaluated specifically.

Just common sense.


exactly,  you dont need a resistor with a constant current driver for example, but something should limit the current to the manufacturers recommendations, common sense.
With my mobile phone I can call people and talk to them -  how smart can you get ?

Headroom

Interesting thread and a very good example why accidental success does not result in true knowledge.

An LED needs a constant current supply, there is no way around that. Thats based on not too complicated and widely published physics. Perhaps that currnt limit can be achieved by some implicit resistance of the components involves, e.g the internal resistance of a battery etc.

However, the question is whether one would want to base a sound design on something that is more a byproduct of a statistically distributed manufacturing process thats only monitored within rlatively wide limits or a design goal kept within close tolerance. A battery for example is a supplier of electrical energy with the usual design goals  being a stable voltage over time and mAh etc. The internel resiststance is what you get with it and it may not even be stated on a data sheet.

A resistors design goal, however, is to have a specified resistance and can be bought at different tolerance ratings. Using components for their intended purpose is obviously more a sound approach. That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.
http://trippylighting.com

http://ledshield.wordpress.com/

retrolefty


Interesting thread and a very good example why accidental success does not result in true knowledge.

An LED needs a constant current supply, there is no way around that. Thats based on not too complicated and widely published physics. Perhaps that currnt limit can be achieved by some implicit resistance of the components involves, e.g the internal resistance of a battery etc.

However, the question is whether one would want to base a sound design on something that is more a byproduct of a statistically distributed manufacturing process thats only monitored within rlatively wide limits or a design goal kept within close tolerance. A battery for example is a supplier of electrical energy with the usual design goals  being a stable voltage over time and mAh etc. The internel resiststance is what you get with it and it may not even be stated on a data sheet.

A resistors design goal, however, is to have a specified resistance and can be bought at different tolerance ratings. Using components for their intended purpose is obviously more a sound approach. That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Yes Sir, you state the case well, no further explanation required.

Lefty

Boffin1

Quote
That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Right, and the whole point of Arduino is to simplfy things for beginners, no direct port manipulation for example, so lets stick to the basics on the hardware side when newbies are asking if a resistor is required  for an LED.
With my mobile phone I can call people and talk to them -  how smart can you get ?

Hippynerd


Quote
That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Right, and the whole point of Arduino is to simplfy things for beginners, no direct port manipulation for example, so lets stick to the basics on the hardware side when newbies are asking if a resistor is required  for an LED.


Now I know what the ugly stepchild feels like.  Lets hide him in the closet when company comes to visit. sigh.

So, the next time someone specifically asks:
"LEDs without the use of current limiting resistors"
And gives a very specific example, we are supposed to tell them that its impossible to do that, and they should never think such dangerous thoughts?
https://sites.google.com/site/rgbledcubes

retrolefty



Quote
That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Right, and the whole point of Arduino is to simplfy things for beginners, no direct port manipulation for example, so lets stick to the basics on the hardware side when newbies are asking if a resistor is required  for an LED.


Now I know what the ugly stepchild feels like.  Lets hide him in the closet when company comes to visit. sigh.

So, the next time someone specifically asks:
"LEDs without the use of current limiting resistors"
And gives a very specific example, we are supposed to tell them that its impossible to do that, and they should never think such dangerous thoughts?


You sir are free to do whatever you wish to your arduino on your projects. However if you post information to people asking for help, some people will probably continue to warn against poor advice that sometimes get posted around here.

So unless your looking for some kind of validation for your methods and advice I don't see where you have a valid complaint to share with us.

Lefty

dhenry

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lets stick to the basics


Essentially you are saying that some members are too stupid to understand the truth so we should tell them falsehood for their own good.

Grumpy_Mike


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lets stick to the basics


Essentially you are saying that some members are too stupid to understand the truth so we should tell them falsehood for their own good.


No we are not saying that and well you know it.

Hippynerd




Quote
That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Right, and the whole point of Arduino is to simplfy things for beginners, no direct port manipulation for example, so lets stick to the basics on the hardware side when newbies are asking if a resistor is required  for an LED.


Now I know what the ugly stepchild feels like.  Lets hide him in the closet when company comes to visit. sigh.

So, the next time someone specifically asks:
"LEDs without the use of current limiting resistors"
And gives a very specific example, we are supposed to tell them that its impossible to do that, and they should never think such dangerous thoughts?


You sir are free to do whatever you wish to your arduino on your projects. However if you post information to people asking for help, some people will probably continue to warn against poor advice that sometimes get posted around here.

So unless your looking for some kind of validation for your methods and advice I don't see where you have a valid complaint to share with us.

Lefty

Im not looking for validation here buddy. Answer the question, what are you suppose to tell someone that asks a valid question, and provides a documented example.

I think the best answer to the question is, yes, that is possible under certain circumstances.
It may be that they need the display to fit in a tiny space, but it only needs to work for 3 days and never used again.

Also, I cant take credit for the design, I just found it on the interwebs, and built one. I can only take credit for experimenting with it, talking to people about it.

Sincerly, Danger McGee.
https://sites.google.com/site/rgbledcubes

Grumpy_Mike

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Answer the question, what are you suppose to tell someone that asks a valid question, and provides a documented example

You tell them the truth. That it is a crap design made by someone who didn't understand what they were doing or understand the damage it is causing.

You point them at your own web site where you did experiments and prove you are drawing current that is over five times the level that the data sheet says damages the arduino.

In the Internet age on the web documents are not worth the paper they are written on. Which you might say includes my site. So do your own experiment and see for yourself.
If you disagree with the results then publish your findings.

Hippynerd

showing some tests is one way, but calling it a crap design by someone that doesnt understand what they are doing is totally subjective, thats just your feelings, not the truth.

The truth seems to be that you may reduce the lifespan of some or all of the parts. If you dont protect your LEDs with resistors or some form of current limiting device, they will probably fail sooner than if you had.

Findings posted. testing ongoing.

I dont absolutely disagree with you, i disagree that things are as absolute as you say.
https://sites.google.com/site/rgbledcubes

smeezekitty


showing some tests is one way, but calling it a crap design by someone that doesnt understand what they are doing is totally subjective, thats just your feelings, not the truth.

The truth seems to be that you may reduce the lifespan of some or all of the parts. If you dont protect your LEDs with resistors or some form of current limiting device, they will probably fail sooner than if you had.

Why willingly reduce the lifespan of components if it could easily and cheaply avoided?
It makes absolutely no sense to me. Datasheets do not lie. There is reason they are only rated at 20-40ma.
Avoid throwing electronics out as you or someone else might need them for parts or use.
Solid state rectifiers are the only REAL rectifiers.
Resistors for LEDS!

CrossRoads

Avoiding failure also means avoiding messy rework. Especially LEDs in a cube, with leads formed around other leads, or perhaps inaccessible.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Grumpy_Mike

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but calling it a crap design by someone that doesnt understand what they are doing is totally subjective, thats just your feelings, not the truth.

The original post, oh what a long time ago it was, asked what assumptions the original designer had made. He asked if it was some consideration over the total thermal energy or something. When you looked at it there was no such consideration, in fact all that had happened was he had looked at the piceved brightness of the LEDs for differing pulse widths. I consider that a crap way to design anything. It shows no understanding of what is actually going on. It is common to see such crap designs at places like instructables. It is a result of either ignorance or a missunderstanding about peak verses continuous current.
Now you might want to replace the word crap with some more politically correct phrase like differently correct but that is up to you. I feel there is little subjectivity with the words I used.

Boffin1

Hey Hippynerd,

I like your your profile   "  Damnit Jim, Im a technician, not a engineer!  "





With my mobile phone I can call people and talk to them -  how smart can you get ?

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