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Topic: IR LED without resistor nano (Read 3828 times) previous topic - next topic

runaway_pancake

"Two equally dim LEDs being visible from further than one equally dim LED?"

Yes.
Example: 1 LED all by itself at X lumens vs. a billboard-full of those same LEDs each doing the same X lumens
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

6v6gt

The OP might get some additional advice if he said exactly what he is doing and also what IR receiver he is using. There may be better alternatives, like for  long range a narrow viewing angle is better so the beam is concentrated.
Here for example is a 3 degree / 100mA IR diode http://uk.farnell.com/osram/sfh4550/led-ir-5mm-850nm/dp/1573495

There may also be more sensitive receivers available for his application.

Grumpy_Mike

Is that really how physics works? Two equally dim LEDs being visible from further than one equally dim LED? This would be news to me if their distance adds somehow.
Read all about it. Electromagnetic radiation is additive. Read all about it.

Yes they really do add up. It is only when it comes to resolving the individual components of the radiation do you need the sensitivity to observe the EM flux from one.

DrAzzy

Is that really how physics works? Two equally dim LEDs being visible from further than one equally dim LED? This would be news to me if their distance adds somehow.
Other matters aside, LED efficiency drops as the current increases - people using large LED grow lights, for example, typically run the LEDs well below their maximum power rating to reduce the power bill. So you get more light out of two LEDs at 20mA each than one identical led at 40mA. 
ATTinyCore for x4/x5/x61/x7/x8/x41/1634/828/x313 megaTinyCore for the megaavr ATtinies - Board Manager:
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ATtiny breakouts, mosfets, awesome prototyping board in my store http://tindie.com/stores/DrAzzy

pwillard


MrAl

Is that really how physics works? Two equally dim LEDs being visible from further than one equally dim LED? This would be news to me if their distance adds somehow.
Hi,

Well that may not be a fact, but it is very possible.  The other variable involved here is the DIRECTION.

For example, we have one LED facing north and one facing south.  Do their emissions add? Certainly not.  Now rotate the south one so it points east, do their emissions add now?  Still no.  Now rotate that same one a little more north, do their emissions add now?  A little, depending on the flux pattern of each LED.  If one LED points north and one north east, then the flux patterns only overlap in the direction between north and north east, which would be very roughly where the hour hand points to 1:30 on the a standard 12 hour clock.

But of course we point them both in the 'same' direction when we want to use two for an IR remote control right?  It still depends on the pattern to some degree, but we estimate the total flux to be the sum of the two which makes it seem twice as strong.  Will it reach a receiver at twice the distance with the same level of light?  It will probably be close although not exact, so maybe a little less than twice the distance or if we get lucky we do get twice, but i think it's a good estimate that we get twice the distance.

The remote i use most these days has three LEDs and it is made by Sony.  It can also read codes from other remotes (very handy).


Grumpy_Mike

#36
Nov 29, 2016, 02:42 pm Last Edit: Nov 29, 2016, 02:43 pm by Grumpy_Mike
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Well that may not be a fact,
YES IT IS.  >:(

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Will it reach a receiver at twice the distance with the same level of light?
Having a higher intensity of light will not go further than the lowest intensity of light you can get which is a photon.

There is no limit on how far a photon can travel if it is not blocked.

But the brighter the light the more photons arrive at given distance and so the easier it is to detect. Light doesn't just go so far and then stop.

MrAl

#37
Nov 30, 2016, 02:06 pm Last Edit: Nov 30, 2016, 02:13 pm by MrAl
YES IT IS.  >:(
Having a higher intensity of light will not go further than the lowest intensity of light you can get which is a photon.

There is no limit on how far a photon can travel if it is not blocked.

But the brighter the light the more photons arrive at given distance and so the easier it is to detect. Light doesn't just go so far and then stop.
NO IT IS NOT :-)

You should have read the rest of the post.

The light direction has to be taken into account, as well as the phase if they are of the same exact wavelength.
I gave a simple example where the two light sources were facing away from each other, there's no way their light can add.
Also, there are experiments that depend on the phase difference even though they are both pointing in the same direction.

Two facing in the same direction would look something like this:
)~~~~~~~  --->
)~~~~~~~  --->

and for our purposes they may add, but these two can NOT add:
<---  ~~~~~~(     )~~~~~~  --->

because they are facing entirely different directions.

The actual addition would come from looking at their radiation pattern and how those patterns overlap.  If both have a bright spot in the middle but they are pointing in slightly different directions, then there is a distance D where only their outer rim patterns overlap so the full intensity will not be had.

Two LEDs can be seen from a farther distance than one because there are more photons in the same area with two instead of one.  That adds to the POWER found at the receiver end, which of course can activate a sensor better.  It does not matter that both LED photons go the same distance, it is that when they do get there there are more of them to act on the sensor and thus provide more of a signal.  This means sometimes we say "the light goes farther" even though the photons dont, just that the influence is stronger.
In other words, the remote works at a greater distance from the sensor.

Grumpy_Mike

Oh dear we are at it again MrAL are we. You have a track record of not understanding things, but thinking you do.

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You should have read the rest of the post.
I did, painful as it was. I am glad I never taught you physics, you would have failed.

Quote
The light direction has to be taken into account, as well as the phase if they are of the same exact wavelength.
No. The phase is only important if the light sources are coherent, in an LED they are not. And the direction is irrelevant. Just assume an isotropic radiator and an emission intensity adjusted to compensate.
Quote
I gave a simple example where the two light sources were facing away from each other, there's no way their light can add.
Yep and a pretty stupid example it was. You can not get any light source that does not have some radiation in some direction, only in your unrealistically simplistic world can this happen, in real life it does not. But there was no point in this example anyway it did not advance the argument.

Basically it all comes down to the derivation of the inverse square law and the area on the sphere of radiation corresponding to the area of the sensing element receiving enough photons to get a sufficiently large signal to noise ratio to allow reliable detection.

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and for our purposes they may add, but these two can NOT add:
<---  ~~~~~~(     )~~~~~~  --->

because they are facing entirely different directions.
That would be true if there was such a thing as a light source that only radiated in one direction. They do not exist.

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This means sometimes we say "the light goes farther"
Yes you say it, but it is total bollocks from a physics point of view, which is what was being expressed in the question I responded to, which was:-
Quote
Is that really how physics works? Two equally dim LEDs being visible from further than one equally dim LED? This would be news to me if their distance adds somehow.
I hope you agree that the answer is yes they do add, and if you define "the light goes further" in a totally none physics way of meaning "the distance limit of sensing".

Smajdalf

I am glad I never taught you physics, you would have failed.
I am glad you never taught me physics and poor children if you teach any. You can define the vague statement "light of two sources add under any conditions" in such way that it is true. But in any reasonable and useful sense it is not true. You say there is no such thing as directional source of light. What about a LED on a meter thick concrete? I guess it will take many years until the first photon from the LED passes the barrier. You want to say two LEDs separated with the concrete adds their intensity in any sense? What about LEDs in other galaxies? But we do not need to go so far ofc. It is common feature that LEDs produce relevant amount of light in limited angle. It is needed to take the different spatial intensity into account when estimating total light produced in given direction just as MrAl said.
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

Grumpy_Mike

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What about a LED on a meter thick concrete?
Read reply #36, I said
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There is no limit on how far a photon can travel if it is not blocked.
Get the end bit - NOT BLOCKED

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I am glad you never taught me physics and poor children if you teach any.
I never taught Physics to children, just grownups.

ad2049q

#41
Nov 30, 2016, 09:03 pm Last Edit: Nov 30, 2016, 09:06 pm by ad2049q
BAD idea running an IR emitter direct from a 5V device like the Arduino.  The "natural" junction voltage of an IR emitter is 1 to 2 Volts when driven hard, so it would try to drop the other half of the Voltage in heating up an arduino digital out.  I prefer the approach of outsider, though 2 or 3 volts to drive the IR is likely to be better than 5.

Choose a transistor Q1 which is more than capable of running the IR at its maximum continuous rated current (for example 5mA), divide by the gain of Q1 (for example 120) so you want about 0.04 mA into the base when arduino digital out is ON (=5V).  If in doubt, 100kOhm from digital out to base is often sensible, though for some IR devices you'd need a different value.

Next measure or look up the voltage across the IR at its max.  If in doubt expect 1.5 V (it could be a little different).  How much resistance should go above Q1 to "use up" the remainder of the external supply voltage ?  Suppose that you have 3.0 Volts external supply.  1.5V / 5 mA = 300 Ohms in place of the 68 in the circuit of outsider.

You now have an external circuit to drive an IR emitter at its maximum (say 5mA) while the base resistor (say 100kOhm) gets +5V. You can do physical testing with just that on pinboard without particularly needing the arduino.  The datasheet of the IR tells you the highest current that you may use it at reliably, and you have briefly got something to work by overdriving it.  So you want more brightness to arrive at the detector.  Possible solutions include :
- duplicate the IR transmitter to get more brightness.  You could have a dozen of them with the kind of external driver of outsider.
- put a lens in front of the IR transmitter to send more of its output in the direction of the receiver [warning! might not be eyesafe]
- put a plastic optical fibre or comparable light guide in between transmitter and receiver.

Be exceedingly cautious with eye safety if thinking of using IR devices more powerful than 1mA and if in any doubt discuss with your supervisor.

Wawa

Every IR (TV) remote I know pushes 100mA or more through the IR LED(s).

The old Philips ones used four LEDs in series on a 9volt battery.
12meters was easy, and if you aimed the remote carefully, it could do 60meters (done that).
Leo..

MrAl

Oh dear we are at it again MrAL are we. You have a track record of not understanding things, but thinking you do.
I did, painful as it was. I am glad I never taught you physics, you would have failed.
No. The phase is only important if the light sources are coherent, in an LED they are not. And the direction is irrelevant. Just assume an isotropic radiator and an emission intensity adjusted to compensate.Yep and a pretty stupid example it was. You can not get any light source that does not have some radiation in some direction, only in your unrealistically simplistic world can this happen, in real life it does not. But there was no point in this example anyway it did not advance the argument.

Basically it all comes down to the derivation of the inverse square law and the area on the sphere of radiation corresponding to the area of the sensing element receiving enough photons to get a sufficiently large signal to noise ratio to allow reliable detection.
That would be true if there was such a thing as a light source that only radiated in one direction. They do not exist.
Yes you say it, but it is total bollocks from a physics point of view, which is what was being expressed in the question I responded to, which was:- I hope you agree that the answer is yes they do add, and if you define "the light goes further" in a totally none physics way of meaning "the distance limit of sensing".

Hello again,


What you are doing is going general when i go specific, then going specific when i go general, and in that way you can say that everything i say is wrong.

So i wont waste my time with you unless you would want to argue (in a debating manner without your mocking tone) one point at a time.

Since the main point is one of distance and the number of LEDs and how they add, i'll reply with that in mind.

Facts:
1.  Light adds based on the number of sources and and the direction of each source.  An extreme example is two LEDs that point 180 degrees away from each other.  As we rotate one LED toward the same direction of the other LED, the light would start to add more and more, creating "more light" at the receiver.
2.  As the light adds once we get the direction optimal, the distance the light appears to travel (called the "Throw" in flashlight terminology) increases, and thus the distance the remote can be used at increases.
3.  The distance light appears to travel is based on the human eye response and there is even a name for it, the "Throw".  The 'Throw" in our case is the distance the remote can successfully operate the receiver reliably.  Yes, photons travel forever unless something blocks them, but the behavior based on the human common experience morphs this into a more tangible definition that every human can relate to without counting EVERY SINGLE photon.  It's the same thing humans do with every experience we have outside of the laboratory: a de facto statistical interpretation of a large number of quantum events.  Like it or not, that's the way it is.






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