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Author Topic: LED Off Delay / LED Fade-In Fade-Out Dimmer - a few questions  (Read 4940 times)

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A. Kato

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Hello. I'm new here so firstly greetings to everyone on this forum, especially to Giorgos Lazaridis, for because of his video I actually found this site at all. I'm a total newbie at electronics plus don't know anyone who could help me, so I searched for a long time for a few (very simple for many of you for sure) LED circuits. The problem with many things I found was, that they were explained on "you know what this means, so I don't need to go into details" assumption. Did I mention I didn't understand half of what they wrote?

Not complaining here, just asking if someone could maybe answer a few of my questions in a simple manner, please.


First about LED Off Delay with dimming effect
http://pcbheaven.com/circuitpages/LED_Off_Delay/

At the moment I plan to use LEDs for max current 20mA and 3-3,2V. I want to build 2 sets of circuits with mixed two colors of LEDs, one for 8 blue + 4 white and one for 6 blue + 6 white. For all I know the parameters of both colors are the same for the LEDs I want to use, so it shouldn't be a problem to treat them as the same I think.

About Schematics for the controller, few things figured out already during typing this, but:
There is only voltage specified 5-15V for power supply, is there any difference which one is '+' and '-' here?

And what are those two connections with 0V on them?

Based on presented schematics, the best option for me would be a 9V supply for 6 rows of 2 LEDs, but "The limiting resistor for each row is 68 Ohms, and a current of 24 mA is drawn". Earlier the author wrote, theat those are schematics for LEDs with operation current 30 mA and voltage drop 3,6V, so how is 24 mA here?

What do I need to modify to use those 20 mA 3-3,2V LEDs?

How do I calculate what resistors (R1, R2 and RP/RPN) I will be needing for them?

There is one connection with 'LEDS' on every schematic, ok, but do I simply connect two '0V' from controller with one from LEDs?

Lastly, capacitor used here is 100uF 25V, but can I use smaller one? I found for example 47uF/250V or 22uF/35V, would those also work? I need shorter fade out time.



As this is long enough already, and I am still studying this LED Fade-In Fade-Out Dimmer schematics
http://pcbheaven.com/circuitpages/LED_Fade_In_Fade_Out_Dimmer/

To put it simply, I would like to make a few circuits like that, but with 100-200 LEDs each. Could be for 12V, could be for 230V (straight from wall socket, if easier to make or explain), but I want it to loop continously for as long, as there is power. Meaning, I switch it on and the LEDs fade in/out/in/out untill I switch the whole thing off. Prefferably one switch for everything but can also live with a few of them.


I would be very thankfull if anyone would be kind enough to help with any of my problems.

kam

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Re: LED Off Delay / LED Fade-In Fade-Out Dimmer - a few questions
« Reply #1 on: March 25, 2012, 15:36:32 PM »
Hello Kato and welcome to our forum.

Quote
There is only voltage specified 5-15V for power supply, is there any difference which one is '+' and '-' here?
Yes there is. The positive (+) is the 5-15 side connection and the negative (-) is the 0V


Quote
And what are those two connections with 0V on them?
Some theory: When we say "10 volts" what we really mean is "potential difference or 10 volts". So, if +is 20 volts and - is 10 volts, then this makes a potential difference of 10 volts (20-10=10), which is exactly the same if we have for + 10 volts and for - the 0 volts (10-0=10). So, some times we use the 0V sign to indicate that this line has 0V potential. In this circuit, it is the same to be used 0v or gnd


Quote
Based on presented schematics, the best option for me would be a 9V supply for 6 rows of 2 LEDs, but "The limiting resistor for each row is 68 Ohms, and a current of 24 mA is drawn". Earlier the author wrote, theat those are schematics for LEDs with operation current 30 mA and voltage drop 3,6V, so how is 24 mA here?

You have 9V supply and you want to supply 3 volts for your LEDs. At 3 volts, your LEDs draw 20mA. You connect 2 leds in series, so each node draws 20mA but it requires double the voltage, which is 6 volts. So you need a resistor to drop 9-6 = 3 volts at 20mA:

R=3/0.02 = 150 Ohms

Let me suggest you to read this LED controlling theory.



Quote
How do I calculate what resistors (R1, R2 and RP/RPN) I will be needing for them?
R2 depends on your application characteristics (fading time). You need to test. You could use for example a 10K potentiometer instead of a resistor and test it. Just keep in mind that it must not be very large. R1 is a small 47 Ohms resistor (do not change) and RP calculation is shown above.


Quote
There is one connection with 'LEDS' on every schematic, ok, but do I simply connect two '0V' from controller with one from LEDs?
Not really understood what you are asking



Quote
Lastly, capacitor used here is 100uF 25V, but can I use smaller one? I found for example 47uF/250V or 22uF/35V, would those also work? I need shorter fade out time.
Sure you can. But you may need to use bigger R3  potentiometer


Quote
To put it simply, I would like to make a few circuits like that, but with 100-200 LEDs each. Could be for 12V, could be for 230V (straight from wall socket, if easier to make or explain), but I want it to loop continously for as long, as there is power. Meaning, I switch it on and the LEDs fade in/out/in/out untill I switch the whole thing off. Prefferably one switch for everything but can also live with a few of them.
I suppose that this circuit will work better for you...
Flexible 555 LED Pulsing (Breathing) Circuit


But for high current applications, i strongly recommend to use something like this (video will be ready within a few days):
High Efficiency High Current LED Buck Driver using the A6210

The breathing circuit (previous link) can then be connected to a DC voltage controlled PWM generator like this one:
Voltage Controlled PWM Generator

And the output of this generator will drive the DIS pin of the LED driver. Otherwise, if you try to drive so many LEDs as you state, you will end up with a big heatsink and a cooling fan for the transistor, since the power dissipation will be HUGE (believe me).  This solution that is like adding lego parts and i believe it will work just fine. One problem: you need to provide yourself the A6210 chip soldered on a socket, otherwise you need to have special tools to solder it
« Last Edit: March 25, 2012, 15:42:41 PM by kam »

A. Kato

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Re: LED Off Delay / LED Fade-In Fade-Out Dimmer - a few questions
« Reply #2 on: March 27, 2012, 02:34:18 AM »
Hello Kam and thank you for Your reply. It was long but easy to understand, so it really cleared a few things for me.

I can't believe I didn't find this site earlier. One post, Your help and the project turned from hiatus into waiting for ordered parts. So, yes, thanks again.

Unfortunantely, the second project is still on hold, as I would have to get this A6210 from abroad, and as a chip only it seems. But for now there is no need to rush, so one thing at a time.

Quote
Quote
There is one connection with 'LEDS' on every schematic, ok, but do I simply connect two '0V' from controller with one from LEDs?
Not really understood what you are asking

What I meant was, how do you actually connect all of this together? The controller, the LEDs and the power source eg. 9V battery.
On the schematics there are multiple doubled ends. Do i just solder all 5-15V and all 0V together and attach them to '+' / '-' of the battery, or..?
From my point of view, lack of a complete schematic of a circuit can turn out to be a problem when trying to get it to work.

As I said, I'm now waiting for parts to be delivered. Which I think schould happen today, as it's way past midnight here. LEDs could take about 2 days. I hope, that after I finally get them, I will be able to present You the results.

I guess the articles on this site will get me busy for quite a while.

kam

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Re: LED Off Delay / LED Fade-In Fade-Out Dimmer - a few questions
« Reply #3 on: March 27, 2012, 08:35:15 AM »
ok i see what you mean. yes, all the 5-15 connections are connected to the +9 of your battery, and all the 0v to the - of battery. From the transistor T1, you connect the anode of the LEDs to the emitter (marked with connector "LEDS"), and the cathode of the leds goes to the - together with the 0V.

As for the A6210, it will be kinda hard to solder it, keep this in mind. You need some sort of hot-air gun.

A. Kato

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Re: LED Off Delay / LED Fade-In Fade-Out Dimmer - a few questions
« Reply #4 on: March 30, 2012, 02:39:38 AM »
Thanks for Your reply. Sorry if maybe my comment about complete schematic seemed a bit ungratefull.. Not true at all.

Today I got all the parts and the LEDs, made a few circuits with different potentiometers. It works like a charm. The best thing about it is the size, with the potentiometer being the biggest element.

Strange thing is, this works ok with 500 kohm potentiometer, 200 kohm or even 50 kohm one, but doesn't with 100 kohm. The LEDs stay slightly dimmed after I cut the power off and don't fade out completely untill I take the battery out. Broken?

Another thing, I connected two circuits to one set of switch/battery and all the LEDs seemed to be affected by both potentiometers, despite being in two separate circuits only connected near the switch. This isn't a big deal for me though, unless I'm doing something wrong here. Both circuits work with no problems alone, so could be just my imagination.

All this is the second stage of my project. Ultimately I want to have two sets of 12 and 18 LEDs with different Fade-Out times < done (?) > and 6 LEDs constantly on, so two switches and one battery are needed for everything. Working on that now.

With 9V and LEDs for 1.8-2V I would need 180 ohm resistor. Which option,
to solder four 47 ohm ones (4*47=188) or
to controll voltage with, lets say 10 kohm potentiometer and maybe 3*47=141 ohm resistance
would work better, if at all? Don't have a 180 ohm one, tests on this matter planned for tommorow.

kam

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Re: LED Off Delay / LED Fade-In Fade-Out Dimmer - a few questions
« Reply #5 on: March 30, 2012, 08:19:42 AM »
Quote
Strange thing is, this works ok with 500 kohm potentiometer, 200 kohm or even 50 kohm one, but doesn't with 100 kohm. The LEDs stay slightly dimmed after I cut the power off and don't fade out completely untill I take the battery out. Broken?
That IS strange indeed i can tell. Maybe broken. Measure it with an ohm-meter.


Quote
Another thing, I connected two circuits to one set of switch/battery and all the LEDs seemed to be affected by both potentiometers, despite being in two separate circuits only connected near the switch. This isn't a big deal for me though, unless I'm doing something wrong here. Both circuits work with no problems alone, so could be just my imagination.
In science people say "do not trust your eye". Put a voltmeter across the battery and measure the voltage. You might probably notice that the battery voltage is slightly less when you put 2 circuits in parallel, which means that either the current supply of the battery is not enough, or the battery is dying


Regarding the resistor, 180 is a value that exists. But if you use a battery you will notice that as the battery fades, the LED will not work that nice. I think that you should better use a voltage regulator (like 7805) to regulate the voltage down to 5 volts. This way, the brightness will be the same regardless if the battery is 6 or 9 volts. Adding a 10K potentiometer to regulate the voltage will add a resistance in the circuit that you do not want it.
And another thing. You've calculated 180 ohms resistor, but you can safely use a 200 or even 220 ohms. Check these values as well. I believe that the brightness will not be that much different.