multiple flashing LED not playing nice

[wilykat]

I wanted to wire up a bunch of cheap multiple flashing LEDs (red-yellow-off, 3 seconds total cycle time) that I got off eBay but they aren't playing nice. If I run just 1 LED they work fine but if I put 2 or more in parallel (each with its own resistor), they start misbehaving and flashing only red (for about 1/10th of a second) then off. it did not matter if I used resistor on anode or cathode side. I am just guessing but these flashing LEDs seems noisy and causing interference? It'd seem silly (and messy) if I have to add 100 capacitors parallel to each LEDs just to cancel out each other's interference.

Is there a way to wire up some 100 of these as I wanted to put it inside my computer and make it look like that old computer with lots of flashing lights from old sci-fi show. (More specifically I wanted the WOPR display LED from the movie War Games)

Available rail are 12v and 5v. As a last resort, I could also use 2 resistors one on each side of LED with a cap parallel across LED.

 

[ronsimpson]

Do you have a data sheet or part number for the flashing LEDs?

 

[wilykat]

There is no datasheet with details, just some basic information:

Size (mm) 5mm
Lens Colour Water Clear
Forward Voltage (V) < = 3.6
Reverse Current (uA) < = 30
Luminous Intensity Typ Iv (mcd) 6000 - 7000
Life Rating 100,000 Hours
Viewing Angle 20 Degree
Absolute Maximum Ratings ( Ta = 25°C )
Max Power Dissipation PM = 80 mw
Max Continuous Forward Current IFM = 30 mA
Max Peak Forward Current IFP =75 mA
Reverse Voltage 5 ~ 6 V
Lead Soldering Temperature 240 ° C ( < 5 Sec )
Operating Temperature Range - 25 ° C ~ + 85 ° C
Preservative Temperature Range - 30 ° C ~ + 100 ° C

I've contacted the seller to see if he can provide more.

 

[ronsimpson]

I am looking for how they think it should be powered.
The LED is not just a LED it includes a IC inside.
I have used a multi-colored LED blinker that goes through 32 colors. It will take hours to find the data sheet. We are using it in production. I have not thought about it in 2 years. I think it can not be used like you are using it. It sounds like the IC is being reset after its first step.

Your part likely is not what I am using. But sounds like a line of similar parts. I will try to find more information. And you will try to get information.

 

[ronsimpson]

Is this what you have?

 

[wilykat]

It is probably similar but I can't tell without opening the LED and putting it under microscope to see and it's pretty dang hard to open up a LED.

Still, would a capacitor help? I have some SMD caps (0.01uF) and solder it between the legs of the LED.

 

[4pyros]

Still, would a capacitor help? I have some SMD caps (0.01uF) and solder it between the legs of the LED.

Cant hurt to try.

 

[alec_t]

You could also try putting a respective ordinary silicon diode (forward biased) in series with the dropper resistor of each LED. So you have +V /\/\/\/ >¦- LED. That should isolate each LED from its neighbours.

 

[ronsimpson]

Try the capacitor across the LED. The ones I use draw very different current depending on where in the cycle they are.

 

[audioguru]

The power supply is not described. It must have a steady output voltage to power flashing LEDs so that they don't cause the voltage to bounce up and down and affect each other. Is the power supply a weak little battery?

Try adding a 100uF or 1000uF capacitor parallel with the power terminals near the LEDs and resistors. 0.01uf will be useless.

I hope the LEDs with their series resistors are really in parallel and not actually a few flashing LEDs in series.

 

[k7elp60]

Another problem that some people don't realize that LED's are also sensitive to light, in fact it is possible to use them as photodetectors. I have put flashing LED's in parallel and they start talking to eachother. I used some that way to flash an orange LED with some green blinking LED's. I had to put some black heatshrink on the green LED's to prevent them from syncronizing with each other.

 

[4pyros]

I had to put some black heatshrink on the green LED's to prevent them from syncronizing with each other.

I never would have thought the effect could be that bad.

 

[k7elp60]

I never would have thought the effect could be that bad.

Here is the schematic attachment. What I found was that with the heat shrink on the to two green LED's that they would get out of sink and the orange LED would flicker similar to a candle. I also learned that if you put blinking LED's in series with other LED's they will all flash in synch with the flashing LED. You can mix colors and make sure the applied voltage of all the series LED's and the flasher does not exceed the ratings of the LED's. Current limiting resistors are not necessary in this configuration.

 

[audioguru]

Your LEDs do not have series current-limiting resistors so when the 9V battery is brand new then the LEDs will instantly burn out.
Or maybe the datasheet you posted is for other LEDs that you do not have.

 

[k7elp60]

Audioguru,
The data sheet on my flashing LED's specifies maxium Vf of 14V.

 

[audioguru]

The description of these LEDs does not say if they have internal current-limiting or not. It says "maximum 30mA" like ordinary LEDs so I think they need you to limit their current.

 

[4pyros]

It says "maximum 30mA"

Whare does it say that????

 

[audioguru]

Where does it say that????

The cheap Chinese (?) two-color flashing LEDs do not have a datasheet but their "information" was given in post #3. It says, "Max Continuous Forward Current IFM = 30 mA". Most ordinary LEDs that need an external current-limiting resistor say that.

 

[Sceadwian]

Series resistors are definitely required, the only exception is if the datasheet explicitly states there is an internal series resistor. On something that's cheap you won't have any, I've seen some limited 12V DC rated LED's that do have internal resistors, but I've never seen blinking LEDs that have internal resistors, although there may be some out there these do not seem to be them. It's just far cheaper and for more simple to use external resistors because it allows the LED's to be used at virtually any voltage.

You'll be very lucky if you haven't fried all the diodes you've tried.

 

[audioguru]

The problem is that the cheap Chinese flashing LEDs do not have a detailed datasheet in English (hint: don't buy that junk).