# Flashing LED Help



## Doc Doom (Aug 28, 2008)

I purchased a bunch of regular and flashing LED online. I connected them using the info on this sight http://wolfstone.halloweenhost.com/HalloweenTech/anemak_MakingLEDEyes.html#SimpleBlinkerEyes. Problem is the flashing LEDs don't flash.
anks 
I did the same thing last year using Radio Shack LEDs and they flashed fine, causing the two static LEDs to flash as well. Are flashing LEDs different? Does the voltage matter? I thought I knew this stuff but I'm stumped.


----------



## The Watcher (Sep 13, 2008)

The ones I have used have been, You just hook them up like the regular ones. But I have pulled some out of things where it looked like they had a micro controller that made them flash. Contact them and tell them what is going on. They should know the product. But Looks like they are using a flashing led to act as a flashing bulb in Christmas lights. So it would be taking the place of a controller. Do the lights come on at all? Doc did you use the led voltage calculator? I went read the whole thing. It is possible if you used to much. From what I get , it might have fused the flasher chip in the led instead of burning it out. If the leds are burning check just the flasher.


----------



## The_Caretaker (Mar 6, 2007)

what your voltage source and current, the flash rate of the led has to do with the current drawn. does the flasher led work by itself?


----------



## Doc Doom (Aug 28, 2008)

I'm using two regular 3mm red LEDs and have tried both a yellow and red flashing LED. Flash rate: 1 per second , Voltage: 2.2V, Current: 20mA 

Power source is 12V wall wart. Closest resistor calculated at 330 ohm so I'm using a 100 and a 200 in series with three LEDs per diagram. All three LEDs burn fairly bright, but none flash. 

Connected two flashers in series without a resistor and a 5.2V wall wart anf both flashed independently.

Can anybody tell what I'm doing wrong? I've got 25 rats waiting for glowing, flashing eyes. 

Thanks in advance.


----------



## The Watcher (Sep 13, 2008)

Are you using 1 flasher for all of them? Are did you put a flasher in each one? The reason I ask, is one flasher might not handle that many. But you might have a voltage problem also.


----------



## The_Caretaker (Mar 6, 2007)

When I did my flaming skull i used 2 flashers and 6 leds with a 20v laptop power supply. I would just put 1 flasher and a 560 ohm resistor and see if that flashes. If not you may have got some none flashers in error.


----------



## Doc Doom (Aug 28, 2008)

I' m using two regular LEDs in series with one flasher.


----------



## corey872 (Jan 10, 2010)

> Connected two flashers in series without a resistor and a 5.2V wall wart an[d] both flashed independently.


That might be a problem. If both flashers in series are going independently, that would seem to indicate they are passing current even when off (which seems to be a pretty weird way to operate, but who knows...). Otherwise, the first one to flash would automatically cut power to the other.

Back to the original issue when you say 'flashing led's don't flash' - do you mean the normal led's stay on constantly and only the flashing led flashes?

If something really strange is going on, you might have to add a small transistor to get the regular led's to work, but we'll have to clarify the situation first.


----------



## Doc Doom (Aug 28, 2008)

corey872 said:


> That might be a problem. If both flashers in series are going independently, that would seem to indicate they are passing current even when off (which seems to be a pretty weird way to operate, but who knows...). Otherwise, the first one to flash would automatically cut power to the other.


I think they are working normally. They both started out blinking at the same time. Either both were on or both were off. I let them go and the blinking got more erratic in each one and then cycled back to the same time again. I think they were actually just a little off in their blink rate and the erratic blinking was when they got out of sync and were cutting of the other's power.



corey872 said:


> Back to the original issue when you say 'flashing led's don't flash' - do you mean the normal led's stay on constantly and only the flashing led flashes?


 What I meant was all three LEDs, (2 regular and 1 flasher) all stayed lit, none of the three flashed. As you said, the flasher should have cut the power to the other two, effectively making them flash as well.


----------



## Doc Doom (Aug 28, 2008)

Ok, made a little progress (I think)but am still having problems.

One regular LED, one flashing LED and 100 ohm resistor in series with 5.2V supply - both flash, brightness ok.

Two regular LEDs, one flashing LED, no resistor, in series with 5.2V supply - all three flash, but dimly.

Two regular LEDs, one flashing LED, 100 ohm (or 200 or 300) resistor, in series with 12.0V supply - none flash, brightness ok.

Two regular LEDs, one flashing LED, no resistor, in series with 12.0V supply - magic smoke escapes from all threee LEDs.

I'm thinking that using a 12v wall wart and up to 300 ohms resistance provides too much voltage across the flashing LED and prevents it from flashing, but it is not enough voltage to let the smoke out. 

Does this make sense?


----------



## The_Caretaker (Mar 6, 2007)

If i remember correctly when i read the specs on the ones i bought the flash rate is based on current. A 12v with the proper resistor should do the trick.


----------



## Scottzilla (Jun 13, 2007)

(Double-posted for some reason)


----------



## Scottzilla (Jun 13, 2007)

Flashing LEDs aren't really like Christmas lights where you can put one in series with a whole bunch of them to make them blink.

Flashing Christmas bulbs have a bi-metal contact that bends back and forth as the bulb heats up and cools down and it acts like a little switch in series with the filament that makes/breaks the circuit. That's why the whole string blinks; it's like there's a switch right in the middle of it.

Flashing LEDs have a multivibrator circuit in them that oscillates at 1Hz or so and turns the power to the LED itself on and off. The multivibrator circuit is always connected to the power though. As a result, these LEDs don't act like a regular switch. 

As the LED blinks on and off, more/less current will flow through it which is why you are getting some success, but if you hook too much stuff in series with the flashing LED the multivibrator won't have enough juice to run and it won't blink any more.


----------



## The Watcher (Sep 13, 2008)

That is what I was wondering also. If it was to much voltage for the flasher. When they said to subtract the Flasher voltage, before figuring the voltage and resistors needed. That made me think it might be. But I certainly wasn't going to tell you to just start trying different configurations with the 5.2. But That is what I would have done. I have found some time to much current can fuse a circuit. That is probably what is happening with the flasher. It speeds up the flasher to where it is so fast, It never really stops.


----------



## corey872 (Jan 10, 2010)

Earlier you mentioned the flashing LED at 2.2V, 20ma. The link you posted showed flashing LED's at 3-5V, so not sure which you have. But assuming the 2.2V flashing is correct - and your 3mm red LED probably needs about 1.8V ...



Doc Doom said:


> Ok, made a little progress (I think)but am still having problems.
> 
> One regular LED, one flashing LED and 100 ohm resistor in series with 5.2V supply - both flash, brightness ok.


So 1.8V + 2.2V = 4V, drop the other 1.2 in the resistor (V/I = R) - so 1.2/.020 = 60 ohms. Your 100 ohm resistor is 'safely' over sized.



> Two regular LEDs, one flashing LED, no resistor, in series with 5.2V supply - all three flash, but dimly.


1.8+1.8+2.2 = 5.8 volts required, so the power supply is a bit undersized on it's own - resulting in the dim light.



> Two regular LEDs, one flashing LED, 100 ohm (or 200 or 300) resistor, in series with 12.0V supply - none flash, brightness ok.


1.8+1.8+2.2 = 5.8 volts required, burn 12-5.8V = 6.2V in the resistor. 6.2V/.020 = 310 ohms required. So that should work with the 300 ohm resistor. One key would be is the power supply really putting out 12V or is it a little higher or lower? You might take a quick measurement with the LED's and resistor hooked up, then try basing a new resistor value off that reading.

One other possibility is hooking everything up with the 100ohm resistor first somehow damaged the flasher due to over voltage. Now it is just stuck on when the 200 and 300 ohm resistors were tried.



> Two regular LEDs, one flashing LED, no resistor, in series with 12.0V supply - magic smoke escapes from all threee LEDs.


Yep, ~5.8v required, 12 applied = magic smoke.



> I'm thinking that using a 12v wall wart and up to 300 ohms resistance provides too much voltage across the flashing LED and prevents it from flashing, but it is not enough voltage to let the smoke out.
> 
> Does this make sense?


Could be, especially if the voltage of the wart is drifting a bit and/or the flashing LED's are highly sensitive to the input voltage. One other thing to consider is if this is a true 'DC' wall wart. Some claim 'DC', but really they're just rectified AC with very little smoothing. The big ripples in the power supply might make the flashing LED unstable.


----------



## Doc Doom (Aug 28, 2008)

Checked flashing LED and it was not damaged. Added additional resistors one at a tme to try to bring the voltage down. Added up to a total on 1210 ohms without any change in flashing or brightness of both standard LEDs or the supposedly flashing one.

I give up. Life is too short.


----------



## corey872 (Jan 10, 2010)

I don't blame you. I would at least look for some different power supply. Something weird is going on if you add that much resistance and it doesn't change brightness, plus the fact things seem to work OK off the 5 volt supply. 

I wonder if the 12 volt supply is not true DC...maybe only half or full wave rectified AC. That would give you an output which pulses from 0 to 12V at the 60Hz AC frequency. It would probably be too fast to see the flickering, but the timer of the flashing LED might reset each time the voltage drops, so it never builds up enough 'elapsed time' to make the flash.

The other possibility is to make things work with the 5v supply. You could try to parallel the two normal LED's then add them in series with the flashing LED and ~60 ohm resistor. That should still get the desired effect, though the normal LED's will be a little dimmer, but don't know if it would be too dim for the intended app or not.


----------



## Scottzilla (Jun 13, 2007)

Here's a simple LED flasher circuit you can build if you're still not having any luck with your flashing LEDs:

http://wild-bohemian.com/electronics/flasher.html


----------



## Doc Doom (Aug 28, 2008)

Scottzilla,
Thanks for the info. I saw that same site but even the simple circuit is over my head. Mty electrical enginnering class was way too long ago. I also want both LEds to blink at th esame time, like eyes.


----------



## hpropman (Jul 27, 2008)

you could also just add a NPN transistor between the flashing led and the regular leds. The flashing led connected to the base of the transistor will turn it on and off connecting the collector and the emitter to bring ground to the non flashing leds. You can connect the collector to ground and the emitter to the series resistor of your 2 regular series leds. and the other end of the leds to your Positive supply. I would also add a 1K between the flashing led and the base of the transistor. this protects the transistor from too much current. radio shack 276-1617 15 pack for 3 bucks.


----------



## HomeyDaClown (Oct 3, 2009)

*Been doing this for years, works fine.*

I can't even remember how many times I've done this...dozens at least.
After seeing all the many flasher circuits out there and since they got rid of the good old LM3909 Led flasher IC chip (was my favorite).

You just need plain vanilla flashing leds, non-fading types along with plain vanilla LEDs (non-high brightness types).

There is a good reference here for just about any situation:

http://www.trainelectronics.com/LED_Articles_2007/LED_101/index.htm

Scroll down the page and look for Flashing LEDs.

It does work.


----------



## corey872 (Jan 10, 2010)

The transistor is another good thought. That would basically be the same as the flicker circuit I use:

http://hauntforum.com/showpost.php?p=395744&postcount=49

Really, the transistor will amplify what ever the LED is doing....flicker, flashing, fading, etc - this is a great way to 'amplify' the effect of the 'special' LED and project it to normal or different color LED's.


----------



## Doc Doom (Aug 28, 2008)

HomeyDaClown said:


> Scroll down the page and look for Flashing LEDs. It does work.


I know it can work. I've done it before. I just can't get it to work with 12V
and the LEDs I bought online.


----------



## HomeyDaClown (Oct 3, 2009)

This is a basic series circuit and current is either there or not depending on the flash state of the Flashing LED. With a 12 volt supply, I use one cheapo 3mm Flasher (Red) in series with either:

4 normal leds or
2 normal leds and a 330 ohm resistor (to give me a voltage drop of about 6 volts) (330 x 0.02 = 6.6) close enough standard value.

The Flasher is the first in the chain starting at the V+ (positive) unless you are using a resistor, then it would be second only to the resistor.

The trick in making it all work is that the Flasher LED does not enter into any voltage or current calculation, it is basically the on/off switch. The power it needs to flash is very little compared to the regular LEDs. Since they are all in series the regular LED(s) current draw is the same throughout the circuit (20 milliamps) and the voltage drop across each LED is 3 volts.

On a 12 volt supply, you simply divide by 3 volts to get the number of regular leds. Then use either LEDs or LEDs and a resistor to satisfy the number.

I am wondering if the Flasher is the first in the chain? Also wondering if your 12 volt supply is battery, regulated or un-regulated? You might want to put a meter on it to see how close to 12 it actually is. A volt or two difference can really throw a wrench in the mess.

Update: I went into the workshop and threw this together and shot a video which will be on YouTube as soon as it gets done uploading.






Sample Single LED Flasher Series Configuration With 2 Normal LEDs.
Power Supply Un-regulated 12 Volt -- Measured 14.73 Volts
With 2 Normal LEDs (3 Volts x 2 = 6 Volts) 
Required Resistor Voltage Drop = 14.73 Volts - 6 Volts = 8.73 Volts
Resistor Value = 8.73 Volts / 0.02 Amps = 436.5 Ohms
Resistor Used = 470 Ohms










As you can see it works pretty well with a few pauses when either the voltage
drifts or the hand twisted power leads get moved)


----------



## The_Caretaker (Mar 6, 2007)

Doc I was playing around with some flickering candles that had the flickering led looking to convert them to 12volts. I hooked them up +12 to led to resistor to ground, all the led did was burn steady it did not flicker. It worked with a 3 volt battery, I found if you put the resistor before the led it starts flickering I also added additional leds to the circuit and they all flickered. Hope this helps you


----------



## HomeyDaClown (Oct 3, 2009)

Doc, did you get it running? 

Now I've created a monster, my son saw me put this together and is building them to sell to his friends.


----------



## Doc Doom (Aug 28, 2008)

HomeyDaClown said:


> Doc, did you get it running?


I gave up trying to use a 12V wall wart and switched to 6V. Two regular LEDs, a flasher and no resistor needed.

Thanks again for all those that tried to help.

Doc


----------



## corey872 (Jan 10, 2010)

Glad to know you got it working. For future reading, there may be something to the resistor placement mentioned above. Since these 'special' LED's are moving into the range of a small integrated circuit as opposed to a generic LED, they might actually need to have the ground tied to a "0 volt" rail. Making the configuration "power>LED>resistor>ground" technically holds the ground side of the resistor at a voltage higher than ground - and that may fluctuate depending on how much power the LED is drawing at the time. With the "power>resistor>LED>ground" configuration, you assure the ground side of the LED is tied to 0 volts regardless of the power flowing through the LED. This would give the microchip controlling the LED the best chance to function properly.


----------



## The_Caretaker (Mar 6, 2007)

In some additional testing I found if you used multiple leds the flashing led had to be the last in the circuit, if the resistor was sized for all.


----------



## Doc Doom (Aug 28, 2008)

Thanks for all the help. I've built many sets of flashing and non-flashing eyes this way and have never had this problem before. I previously used Radio Shack LEDs but this time need a whole bunch and the three RSs in my neighborhood had about four LEDs between them. I ordered them on ebay and they were shipped directly from China. 

In my experience, it doesn't matter whether the flashing LED and/or resistor comes first or last. 
Doc


----------



## goneferal (Sep 8, 2010)

*Blinking/ flickering LED's*

This isn't to be self promotional, but it is a compilation of my ENDLESS searching the web for this sort of info. I think the wizard link at the end will help the most like it did me. http://goneferalinid.blogspot.com/2010/09/led-flicker-lantern-take-one_09.html


----------

