# LED Flicker Discussion



## heresjohnny

I got a lot of real good feedback on the LED flicker poll, and I have applied that feedback to develop a new flicker that I think most will like. Please check it out at http://johnnyspage.com/LED%20Flicker.htm, click the jack o lantern titled 'mystery flicker' and let me know what you think.

Thanx!


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## Otaku

I like the Mystery Flicker. It's similar to the LED tea light, but significantly brighter. It also seems to have a dim-to-bright cycle. I gotta go get some of the tea lights and see if I can change the LEDs. Looks good, heresjohnny!


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## Zombie-F

Me likey! Very good.


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## Dr Morbius

Now..would those work in a lantern hack?


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## heresjohnny

I think it will work very nicely in a lantern. I have several small ones from Big Lots waiting for the time...

The mystery flicker is the schmitt trigger circuit (flicker 1 by snovtill) with a 15k resistor replacing the 390k resistor. Per the author of the circuit, I replaced the 390k with a potentiometer and adjusted it until I liked the effect, with the result being 15k. I like this circuit because it is easy to build for a circuit, and the components cost less than $2.00 (I am so cheap!). I plan on laying out a circuit board for this and making some in quantity, will post when I'm done.


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## gmacted

Very Nice!!!!! I would have never guessed it was an LED.


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## mrklaw

When I looked for 4585 schmidt triggers on the jameco website, I got the following list:



Code:


Passive Components:Capacitors:Tantalum  	 	1  	View List
Passive Components:Capacitors:Ceramic, Disc 	 	1 	View List
Passive Components:Frequency Control:Crystals 	 	1 	View List
Interconnects:D-Sub Connectors:Hoods 	 	 	1 	View List
ICs & Semiconductors:Logic, CMOS:74AHC Series 	 	2 	View List
Test, Tools & Supplies:Tools:Hand Tools, Strippers 	2 	View List
Wire & Cable:Management Products:Clips & Clamps 	1 	View List
ICs & Semiconductors:Logic, CMOS:74HCT Series 	 	1 	View List
Interconnects:Terminals:Solderless 	 	 	8 	View List
Electromechanical:Hardware:Tape & Mastics 	 	1 	View List
ICs & Semiconductors:Logic, CMOS:74HC Series 	 	2 	View List
ICs & Semiconductors:Logic, TTL:74ALS Series 	 	2 	View List

Is one of these the right component? None of the ones I looked at said 4585 or schmidt trigger when I clicked on them.


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## heresjohnny

Damn, there is an error in my part list, sorry bout that. The number is 4584, and the jameco part number is 13768, try that. I will fix the page as soon as I get home tonight, thanks for catching that!


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## gmacted

here'sjohnny,

I just had an idea for your flicker circuit. This could be used in "Zombie-Fs" unearthed coffin. You would just have to replace the red LEDs with green ones. I may need to add a few more LEDs however to get the right brightness. How much current can the schmidt triggers sink?

gmacted


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## Otaku

heresjohnny,
I picked up one of the LED tea lights at Walgreen's and yes, it is hackable. I did this one the hard way, by taking the whole thing apart to get to the LED. Lots of de-soldering. The easiest way to replace the LED is to cut away some of the molded silicone from the base of the LED, cut the exposed leads, and solder the new LED directly to the leads. Verify the polarity so you only have to do it once. I plan to also wire in a 2AA battery holder to extend the battery life.


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## Otaku

Update on the tea lights - the LED can be easily replaced with a brighter one. but it drains those little batteries fast. The circuit will handle a 4.5-5VDC input, so I wired a 3AA pack to the terminals and the LED is now VERY bright. If you use a narrow beam LED just bend the leads to the side and stick on a small diffuser.


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## heresjohnny

otaku, thanks for the info. I will have to try this hack myself and add the results to my LED flicker page. Do you still get a nice flicker with the brighter LED?


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## Otaku

Yes, the flicker rate and voltage variability seem to be unaffected by the higher input voltage.


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## heresjohnny

I was messing around this weekend with a cheap way to build one of these circuits. I tried using card stock, marking the holes for the 2 ICs, inserting the ICs, then the jumper wires and other components, and soldering the whole thing together. Worked like a charm! I wouldn't want to use this technique for anything critical, or high current, but for a 20 mA LED flicker circuit it should be okay. This is the snovotill circuit, nice small package, runs off a 9 volt battery.










Could put this in a small jack o lantern and get this effect

http://johnnyspage.com/video/mysteryFlick.wmv


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## NecroBones

Looks great! I may need to start building some. Cheap is always good. Of course, laziness often sets in and I build nothing. Heh. 

Perhaps I missed it, but did you have a circuit diagram for it?


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## heresjohnny

NecroBones I have a page devoted to flicker circuits here http://johnnyspage.com/LED%20Flicker.htm
including the circuit built in the picture (snovotill's firelight flicker, with an 18k resistor instead of a 390k).


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## Dr Morbius

I'm gonna have to build some of those. Nice work HJ!!


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## NecroBones

Yeah, I was looking there and only saw the parts list. I didn't realize there was a link above the jack-o-lanterns for the diagram.


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## Otaku

Hey, HJ, let me know how those big LEDs work in a flicker circuit. I may want to get some for the tea lights.


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## heresjohnny

Otaku said:


> Hey, HJ, let me know how those big LEDs work in a flicker circuit. I may want to get some for the tea lights.


Well I finally got around to trying the 10mm 60,000mcd LEDs in the flicker circtuit and they work great! By far the brightest LED flicker I have seen yet. Here is the video http://www.johnnyspage.com/video/flicker10.wmv, details at http://www.johnnyspage.com/LED%20Flicker.htm. The difference can really be noticed if you compare the 2 snovtil circuits, the one with the 60,000mcd shows the edges around the mouth, nose and eyes very clearly compared to the others.


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## heresjohnny

More LED Flicker work, gonna post this on the flicker thread. Used Otaku's tea light hack with a 10mm 60,000mcd LED. Here is the before http://www.johnnyspage.com/video/Flicker12a.wmv and here is the after http://www.johnnyspage.com/video/Flicker11a.wmv. See http://www.johnnyspage.com/LED%20Flicker.htm for details.


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## DeathTouch

Awesome job Johnny. So which one did you perfer?


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## Otaku

Wow, HJ, that's a nice flicker! I bet that would look good in a lantern, too. Where can I get these LEDs?


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## Crazy2ScareU

very nice johnny,ever think of selling them to us less unfortunate in the brain department?


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## killer13

I would be very interested in helping with the circuit board! I have been thinking of doing the same thing myself. We might as well combine resources. 

Let me know if you are interested.


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## heresjohnny

Crazy2ScareU said:


> very nice johnny,ever think of selling them to us less unfortunate in the brain department?


If I can somehow generate some extra ones I might just do that.


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## heresjohnny

killer13 said:


> I would be very interested in helping with the circuit board! I have been thinking of doing the same thing myself. We might as well combine resources.
> 
> Let me know if you are interested.


Alway interested in sharing, I think there was a group buy on some circuit boards, but now I think the hacked tea light is better (and easier). I'll let you know.


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## heresjohnny

Thanks!



DeathTouch said:


> Awesome job Johnny. So which one did you perfer?


Deathtouch I prefer the LED tea light with the 60,000mcd, about the same cost but must simpler and it can provide direct lighting.



Otaku said:


> Wow, HJ, that's a nice flicker! I bet that would look good in a lantern, too. Where can I get these LEDs?


The LEDs come from BestHongKong, i got them on ebay in lots of 50, paid about 15-20 cents each total.


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## heresjohnny

I found 14 of the T-Lites at a Walgreens today and bought all of them. They are on clearance for $2. This is the flicker you can make from them http://www.johnnyspage.com/video/Flicker11a.wmv. Since making this video I have found you can shove tinfoil up into the plastic candle top, and that will restrict the light to the candle element, will post a how-to update and new video soon.


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## gmacted

Heresjohnny,

I decided to build the snovotil circuit linked to on your web page, but I found a problem with your resistor value change and and want you to double check your values.

The value I'm questioning is the 390K ohm to 15K ohm resistor change you made. According to snovotil, decreasing the fequency of the sampling oscillator will cause more of a flicker result. I agree with this statement. A Schmitt Oscillator has the following formula:

f = 1 / (R*C * ln**VT+ * (Vcc - VT-)) / ((VT- * (Vcc - VT+))))

From the 4584 datasheet and the circuit Vcc = 9V, VT+ = 5.3, VT- = 4.6. This results in f = 1/ (R * C * some constant). The value is somewhat unimportant, but the formula is important. The formula is basically telling you that the frequency is inversly proportional to the resistance. If you want to decrease the sampling frequency, you need to increase the resistance value. You didn't do this.

I built the circuit with your 15K ohm resistance change and it didn't flicker at all, it just shimmered slightly.

I changed the 15 K ohm to 1 Meg ohm and it worked nicely as a flicker circuit.

I guess the bottom line is that I think that your resistance value (15K) stated on your web site is incorrect. If someone builds the circuit as you recommend, it won't work. as in your video. Could you check the value of the resistor again. I think it should be more like 1 Meg ohm.

BTW thanks for compiling all of the information on LED flicker circuits. I think its great!


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## heresjohnny

Thanks for checking on that gmacted. I double checked the circuit, and I am actually using an 18k across pins 5 and 6, in fact I have built three of the circuits and they flicker like the video. I will correct the value in my page, though I don't understand why it is working with the frequency being inverse to the resistance. I will definitely try a 1 meg myself to see how it works!

I have noticed (and the inventor pointed out) that this circuit is sensitive, and if the power leads where too long shielding it would make it start flickering. I have also stopped using the 47 pF on the advice of the inventor. I will also correct this.

I do need to say that snovotil didn't tell me the frequency would go down with resistance, I assumed that after playing with a potentiometer and measuring the final flicker.


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## gmacted

I still don't understand how you got a flicker using 18K ohms. I'm just going by what the formula says and what my practical experience with the circuit tells me. I needed a ~ 1 Meg ohm resistor to get it to work and that agrees with the formula. I'll be curious to see what happens to your circuit when you use a 1 Meg resistor. I got a perfect flicker with it.

Where are you using a 47 pF capacitor? I am using a 100 pF capacitor for the 2 MHz oscillator and a 47 nF capacitor for the 200 Hz oscillator.

There is one other comment I would like to make about the information on your web site. You said that you don't need to use all four of the schmitt triggers. From what I can see that is incorrect. According to the datasheet, each pin on the 4584 can either sink or source 10 mA (max.). Since you are trying to sink ~20 mA with the LEDs, you will need to connect at least two of the schmitt triggers to sink that much current. It may work for some time with one (since datasheets are usually very conservative in their ratings), but you would be pushing the recommended current rating of the device. To be safe, I would recommend at least two of the schmitt triggers to be wired together.


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## heresjohnny

gmacted I am an electronics amatuer that is pretty good at soldering and tinkering, the additional info about the circuits are things I am passing on from the inventors and other users, for example not using all of the schmitt triggers was presented as a theory, which came out of a exchange with the inventor. Based on what you said I need to modify that to use single normal LEDs (not sure of the current draw of a typical LED of the top of my head)?

If you look at http://members.shaw.ca/novotill/FireLightFlicker/ you will see a 47pF hanging off pin 1 of the 4584. I was told by the inventor that this was not really necessary due to internal capacitance of the schmitt trigger.

I know someone else that has succesfully built the circuit, but he used a potentiometer in the lower frequency oscillator and I am trying to find out the resistance value he ended up with. As to why mine is working, I dont know, but they are working! I do appreciate the feedback, I want to try and convey correct information. Please let me know what you find out about the 1 meg resistor, I am going to try this myself soon.


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## gmacted

heresjohnny said:


> gmacted I am an electronics amatuer that is pretty good at soldering and tinkering, the additional info about the circuits are things I am passing on from the inventors and other users, for example not using all of the schmitt triggers was presented as a theory, which came out of a exchange with the inventor. Based on what you said I need to modify that to use single normal LEDs (not sure of the current draw of a typical LED of the top of my head)?
> 
> If you look at http://members.shaw.ca/novotill/FireLightFlicker/ you will see a 47pF hanging off pin 1 of the 4584. I was told by the inventor that this was not really necessary due to internal capacitance of the schmitt trigger.
> 
> I know someone else that has succesfully built the circuit, but he used a potentiometer in the lower frequency oscillator and I am trying to find out the resistance value he ended up with. As to why mine is working, I dont know, but they are working! I do appreciate the feedback, I want to try and convey correct information. Please let me know what you find out about the 1 meg resistor, I am going to try this myself soon.


You can still use two LEDs. The current won't change if you take out one LED. It's simple ohm's law (V = I * R where V is voltage, R is Resistance, I is current). The only resistance you have in the circuit is the resistor. The LEDs have a forward voltage drop and a forward current. In order to operate the voltage source must be greater than the forward voltage drop and the current must be approximately equal to the forward current (usually ~15 - 20 mA). If you only use one LED (with a forward voltage of 3.2V) with a 9V battery, the resistor value will need to be R = (9 - 3.2) / 0.02. R = 290 ohms. If you use two LEDs the resistor value will need to be R = (9 - 3.2 -3.2) / 0.02. R = 130 ohms. In each case you still need 20 mA wether you use one or two LEDs.

Basically I'm saying that you should use two of the six Schmitt devices to sink the LEDs current. Since you circuit is drawing 20 mA, you need to sink that current with two Schmitt devices.

I hope this makes sense to you.

As far as the 1 meg resistor is concerned, that is the value that I'm using and it works well and it agrees with the formula also. I'm not sure why yours is working with a 18K ohm resistor. It doesn't make sense.

I agree that the 47 pf capacitor is probably not needed as the input capacitance of the device is probably that much already. Pin 1, still however, should be connected to GND in any case.


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## heresjohnny

Lol, yeah I know ohms law, I certainly was not paying attention. I have decided to simply drop that idea from the web page.

OK, I heard from the other guy, he thinks the pot was set around 1 meg also, so that makes me the odd man out  So I am hoping that I put a 1 meg resistor on, it looks wonderful and I forget about the 18k resistor. I am also getting a mod from a user that uses a cap to keep the LED from turning completely off, will add that also. Thanks for your help gmacted.


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## gmacted

heresjohnny said:


> Lol, yeah I know ohms law, I certainly was not paying attention. I have decided to simply drop that idea from the web page.
> 
> OK, I heard from the other guy, he thinks the pot was set around 1 meg also, so that makes me the odd man out  So I am hoping that I put a 1 meg resistor on, it looks wonderful and I forget about the 18k resistor. I am also getting a mod from a user that uses a cap to keep the LED from turning completely off, will add that also. Thanks for your help gmacted.


I don't think you should drop the idea from your web site at all. I think you should keep it there. I thought it got a very positive response. It gives members alternatives and resources to try things on their own. I would have never thought of doing something like this if I hadn't seen your web site. I built this circuit and plan on using it in my unearthed coffin. I think the flickering green light will look cool.

I'm only trying to provide you with information that will make your site more accurate.

I've never seen a potentiometer that goes to 1 meg. I'd like you to try a 1 meg in your circuit and see if it works.


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## heresjohnny

Learned a new trick when hacking an LED tea light with an Ultra Bright LEDs. The Ultra Brights are very directional, but a dab of glue on the tip of the LED from a hot glue gun will make a cheap and easy diffuser. If you're inclined you can even stretch it out a little as it cools and make it shaped like a flame.


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## heresjohnny

I found two additional LED tea lights that can be hacked with ultra bright LEDs and AA batteries, the Funkin ($2.99) and the JoAnn fabric's special ($1.98). I think the JoAnn fabric flicker is more subtle, but both work. Same technique as in Otaku's how-to, take it part, cut of he old LED, solder in a new Ultrabright and AA battery holder. Very simple. You will need to do something to dress up the candle when your done is you use the large 10mm LEDs like I did, you will not be able to put it ,back together. The pictures show the result of hot gluing the top on to the LED so the beam shines into the original diffuser. I glued some tinfoil into the inside of the top to keep the light from shining through the top of the candle. I was planning on masking tape or papermache. Alternately, if you are not showing the candle directly but plan on using a lantern or lamp etc, you can leave the LED exposed and dab some hot glue on the end of the LED, wich will give you a nice diffused point source that is flickering.


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## gmacted

Thanks for the info heresjohnny! I may try that hack for my pumpkins this year. Hopefully I'll have the time.


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