LEDs without the use of current limiting resistors

I usually stick to digikey and mouser for small quantities

I got to give props to arrow and avnet, they are 2 of our suppliers at work, and hey, they buy me nice lunches hehe, and both have good support even if they dont know who you are

DK on the other hand sent me 250 .1uF 805 caps, which were suposta be 5Amp rectifier diodes in a SMC package (for those not familiar with surface mount packages its a grain of rice vs a jellybean, never mind its totally the wrong component), and I got a deadline on (next)Tuesday ... I had to get bitchy with them and reorder somewhere else cause a couple weeks later and people still cant find info on the mix up is not cool, so they are a bit on my list right now

they buy me nice lunches hehe

Someone at work got a drawer full of atmel's USBKEY, as free samples. That would have been worth some serious money during the height of ps3 jailbreak.

Just an analogy here, my neighbour , when he decides to drive to the casino, never wears his seat belt.

Both of these choices are his ( although the seat belt is compulsory ) I am just trying to show his mentality here.

He has never been killed yet in 50 years of driving without a seat belt. If asked about it he might well say " I heard of someone who had a crash and was thrown out of the burning car , and survived because he wasn't wearing a seat belt " There are a few variations of this.

The point is, if there was a forum for newcomers to learn about driving, should we be saying " don't worry about wearing a seat belt, I know someone who has got away with it for 50 years ! " ?

Another point is, wouldnt at least one LED manufacturer jump on the bandwagon and say " you don't need a resistor with our LEDs " and sell more ? Perhaps they know something, being manufacturers.

wouldnt at least one LED manufacturer jump on the bandwagon and say " you don't need a resistor with our LEDs " and sell more ? Perhaps they know something, being manufacturers.

They do, that's why you never hear an LEd manufacturer (reputable ones) who says "you have to use a resistor with LEDs".

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.

dhenry:

wouldnt at least one LED manufacturer jump on the bandwagon and say " you don't need a resistor with our LEDs " and sell more ? Perhaps they know something, being manufacturers.

They do, that's why you never hear an LEd manufacturer (reputable ones) who says "you have to use a resistor with LEDs".

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.

Wrong.

Manufacturers supply things called "datasheets" with their parts. In the datasheet there's always a section titled "Absolute Maximum Rating". The values in there are determined by people who know stuff about their product and know what power is likely to damage it.

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.

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.

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.

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

Lefty

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.

Boffin1:

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?

Hippynerd:

Boffin1:

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

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.

dhenry:

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.

retrolefty:

Hippynerd:

Boffin1:

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.

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.

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.

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.

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.

Avoiding failure also means avoiding messy rework. Especially LEDs in a cube, with leads formed around other leads, or perhaps inaccessible.

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.

Hey Hippynerd,

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