LED Tea Light Candle

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moe
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LED Tea Light Candle

Post by moe » Sun Sep 17, 2006 10:19 am

Anyone have plans or a site to build a LED Tea Light Candle that will flicker.
I thought there was a plan in Nuts and Volts years ago that used a yellow and blinking red LED but can't find it.
Thanks
Moe

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philba
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Post by philba » Sun Sep 17, 2006 11:38 am

as I recall it was a basic stamp project using an external driver board. vast overkill. Probably about 1 year ago (sept issue, I think).

I made one based on a PIC12F629. Total parts cost was a couple of bucks. Schematic image: http://www.geocities.com/pcbs4less/candle/candlev12.gif
Source code: http://www.geocities.com/pcbs4less/cand ... -v1asm.txt

There were a number of things I didn't like about the N&V version, foremost was the way it flickered. I recorded the actual light from a candle as it flickered and then embedded it in my program via PWM.

The other thing I didn't like was the multiple color LEDs, I tried that out and couldn't get it to look very realistic.

The led I used was an ultra bright 20mA device. I tried a bunch of them and selected a Lumex ssl-lx5093SYC due to its color and output. I think adding a second similar LED would be good and have it slightly out of phase with first.

Placed in a paper bag or a thin walled PVC pipe, this looks pretty realistic. I beta tested the flicker on a number of friends and they all thought it was very realistic.

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Post by Dean Huster » Sun Sep 17, 2006 6:09 pm

Won't you have to run it from a pretty good source of power to actually substitute for a tea light in a food warming application? :)

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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jollyrgr
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Thanks For The Reminder

Post by jollyrgr » Sun Sep 17, 2006 9:32 pm

I saw flickering LED devices at the dollar store (one up, non chain store). They had flickering LED candles two for $1 based on an LED. Looked real nice and was about the size of a Tea Candle. Ran on watch batteries I believe.
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Post by bigkim100 » Tue Sep 19, 2006 4:26 pm

Nice little circuit Philba Howlong do your tealights last?
All the ones that I have tried seem to only last a hour or 2 at the most. Is there any way to increase the life of the batteries, or use a supercap Unfortunatly, I realise that to keep the design down to "tealight " size...the size, and therefore the life of the batteries has to be kept tol a minimum.
Kim..The man with the cute little girls name...and Frankensteins face and body.

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philba
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Post by philba » Tue Sep 19, 2006 5:12 pm

that version is powered from a wall wart so pretty long :)

I've got a somewhat different design that uses 2 AA batteries and runs for about a week with the photo transistor turning it off in the daylight.

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Post by k7elp60 » Wed Sep 20, 2006 7:54 am

Get two flashing LED's of the same color. Connect them in parallel, wire them in series with a orange LED and a 9V battery. It will last for days.
When the power is first turned on the orange LED flashes normally, but in a short time the two flashing LED's get out of sync with each other and the
orange LED flickers like a flame.

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philba
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Post by philba » Wed Sep 20, 2006 8:47 am

k7elp60 wrote:Get two flashing LED's of the same color. Connect them in parallel, wire them in series with a orange LED and a 9V battery. It will last for days.
When the power is first turned on the orange LED flashes normally, but in a short time the two flashing LED's get out of sync with each other and the
orange LED flickers like a flame.
uh, I'm sorry but not even close. put that in a paper bag (white or brown) and ask 10 people if it looks like a candle is in the bag - you will get 10 NOs. I spent a lot of time looking into flickering. it is not flashing - the brightness varies in a predictable fashion though there is a fair amount of randomness. Some people have used "strange attractors" http://en.wikipedia.org/wiki/Strange_attractor but recording the flame intensity worked better for me.

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Post by Gary » Fri Sep 22, 2006 12:22 pm

No Dean, they are not used for warming food. Just a warm glow.

Restaurant supply stores sell electric ones to replace the little votive candles. Some of the votive candles last 24 hours, and are about 2 inches high. The battery powered versions probably last for many days. They are popular in some restaurants now.

I'd suggest getting one from a restaurant supply store and hacking it.

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tea candle

Post by Timothy Rasch » Sat Sep 23, 2006 8:46 pm

Hi I do remember the issue was a October issue maybe 2000 or after. I will look for it when I have time. It used flashing Leds: red,2 yellow like you said built in a candle . I built it with just the bare flashing leds and was not too impressed. Tim Rasch [email protected]

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tea candle

Post by Timothy Rasch » Sat Sep 23, 2006 9:21 pm

Hi Again, I found the article in Nuts/Volts October 2000 on page 92.You were right one yellow [non flashing] in series with two flashing red leds in parrelel connected to +6v. The other circuit had two flashing red leds from +6v[ in parrelel] to ground through 100 ohm 1/4w ,a 10 ohm 1/4w at the high side of the 100 ohm going to base of a 2n2222,emitter to ground ,a 6v colored lamp from the collector to +6v. They suggest to try a 12v colored lamp to produce a nice candle effect. The lamps can have a current rating up to 200 ma. I didn't try the later circuit . I think it will work better. BTW the article is called: FLAME FLICKER SIMULATOR.It's designed to be put in a jack-o-lantern ,etc. Thanks for bringing up the subject!!!!!
Tim Rasch [email protected]

Jim Remington
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Candle simulation with LEDs

Post by Jim Remington » Mon Oct 09, 2006 9:54 pm

You all might look at Circuit Cellar #147 (Oct. 2002). Ching and Land made an effective candle simulation for theater productions using a yellow LED driven by PWM. The candle flicker was modeled using a random number generator and low pass filter to simulate actual, measured flame dynamics (1/f noise), previously published in a Japanese engineering journal. C code for the Atmel AT90 may be downloaded from the Circuit Cellar web site. I've used their model and it works very well.

Cheers, Jim

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Candle simulation with LEDs - addendum

Post by Jim Remington » Mon Oct 09, 2006 10:06 pm

It seems that Philip Ching did the candle simulation as a student project, and the whole thing is also published on the web at Cornell. See


http://instruct1.cit.cornell.edu/course ... /index.htm

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Post by ku7485 » Tue Oct 10, 2006 6:47 am

In an Nuts & Volts issue (December, 2002, #12), there was a really good flickering flame circuit in the Electronics Q & A on page 26. It used a combination a 555 timer "to produce the most realistic effect." If you want moe, I guess I can scan the page and send it to you if you don't have the issue.

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