Flickering LEDs for a display sign

Thread Starter

Guitar Fogie

Joined Apr 10, 2019
2
I am with a community theater troupe and have been asked to replace "Christmas lights" with something using LEDs. It is desired that they be able to "flicker". I have identified 2 options which will provide continuous light but I am wondering if anyone can help me come up with a relatively simple means to get the flicker option. The sign is approximately 36"x36" with black lettering over a frosted lens.

Option 1: LED strips. I have 4 strips (1 watt/100 lumens each)from Model JUL10WM4 (www.bazz.ca). These have 4 conductors and a switch to choose one of two brightness levels.
The unit is powered by a 120ac/12dc 1 amp transformer plug. I think I can wire it up so the switch will choose either continuous or flicker mode instead of changing the brightness.

Option 2: E12 (chandallier) base bulbs (200 & 400 lumins each)(2.2 & 4.4 watts) 120vac.
I can wire up 4 sockets to cover the area and use a DPST switch to go from steady to flicker.

My electronic experience is somewhere between beginner and intermediate levels.
Anybody have any suggestions that might help me out here?
Thanks a bunch.
 

cmartinez

Joined Jan 17, 2007
6,457
I am with a community theater troupe and have been asked to replace "Christmas lights" with something using LEDs. It is desired that they be able to "flicker". I have identified 2 options which will provide continuous light but I am wondering if anyone can help me come up with a relatively simple means to get the flicker option. The sign is approximately 36"x36" with black lettering over a frosted lens.

Option 1: LED strips. I have 4 strips (1 watt/100 lumens each)from Model JUL10WM4 (www.bazz.ca). These have 4 conductors and a switch to choose one of two brightness levels.
The unit is powered by a 120ac/12dc 1 amp transformer plug. I think I can wire it up so the switch will choose either continuous or flicker mode instead of changing the brightness.

Option 2: E12 (chandallier) base bulbs (200 & 400 lumins each)(2.2 & 4.4 watts) 120vac.
I can wire up 4 sockets to cover the area and use a DPST switch to go from steady to flicker.

My electronic experience is somewhere between beginner and intermediate levels.
Anybody have any suggestions that might help me out here?
Thanks a bunch.
You could use a triac and a timer circuit to switch the power supply on and off. It's not a very challenging project ... it would be more fun if you were able to program flickering patterns. Or perhaps you could connect it to a computer's serial port and program those patterns by switching the RTS output. Can you do a little programming in Visual Basic, for instance?
 

BobTPH

Joined Jun 5, 2013
2,019
Simulating "Candle Flicker" is not easily done
With a microcontroller it is not difficult at all. I tried this l, thinking I would have to experiment for a while.

First attempt was an 8 bit random number generator to change the duty cycle of a PWM signal every 100 ms. It worked beautifully, exactly the effect I wanted.

Bob
 

cmartinez

Joined Jan 17, 2007
6,457
With a microcontroller it is not difficult at all. I tried this l, thinking I would have to experiment for a while.

First attempt was an 8 bit random number generator to change the duty cycle of a PWM signal every 100 ms. It worked beautifully, exactly the effect I wanted.

Bob
How on earth did you write a RNG for an MCU? ... I'd very much like to know the assembly algorithm to do that.
 

djsfantasi

Joined Apr 11, 2010
5,577
Depends on the MCU and what language it’s programmed in. If it’s a high level language, like C, they should have a built-in pRNG that’s good enough for candle flicker. A quick Google search will turn up many code examples. Like this one.
Not all of them are good.
 

djsfantasi

Joined Apr 11, 2010
5,577
Also, check out NeoPixels. They are individually addressable LEDs and come in strings. Again with a MCU, it is not difficult to create a string of individually “flickering” LEDs.
 

DNA Robotics

Joined Jun 13, 2014
499
50 RGB LED 5m String, Pseudo Random Flash
Item #: 31984 OP Sale: $9.95

Pack of 100 - Flashing RGB 5mm LED
Item #: 32889 OP Sale: $4.95
Pack of 100pc.

5mm (T1-3/4) 3 Color Red/Green/Blue LED that rotates through a cycle of Blue, Red, Green at ~1 color/2sec for ~3 sec. then increases rate to 1color/sec. then 3colors/sec. then repeats sequence.
Must Have Current Limit Resistor
Max forward current 20mA continuous. (Use ~470 ohm for 12V)
Wavelength: R630/G530/B465nM,
Min. output: R4000/G7000/B5000mcd .
Typ. Forward Drop: R2.4/G3.4/B3.4V.
Max reverse Voltage =5VDC.
 

Alec_t

Joined Sep 17, 2013
10,354
Be aware that flickering lights can induce epileptic seizures in some individuals. Critical frequencies to avoid are in the sub-10Hz range from what I've read.
 

Bernard

Joined Aug 7, 2008
5,255
A flickering LED can be used as a signal source to drive a string of LEDS or a string of 120 V bulbs.
I've used 120 V incandescent bulbs but have not tried 120 V LED bulbs.
 

Thread Starter

Guitar Fogie

Joined Apr 10, 2019
2
You could use a triac and a timer circuit to switch the power supply on and off. It's not a very challenging project ... it would be more fun if you were able to program flickering patterns. Or perhaps you could connect it to a computer's serial port and program those patterns by switching the RTS output. Can you do a little programming in Visual Basic, for instance?
Sorry for the delay. Washer crapped out and the need for replacement has taken priority. As far as programming goes I have zilch knowledge/skill in that are so it would be a non starter. I read on another forum about tne idea of wiring up a "blinking" led at the start of the chain that I have. In theory, this should cause all to blink.

This project has been pushed to the back burner for now. Thankyou for all the input and interest.
 
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