A Funny Thing Happened on the way to this circuit

[SparkyCal]

I created a circuit that utilizes a 555 timer that flashes a bank of blue LEDs driven by a 12 volt battery

It works fine. Then I had the bright idea, of creating another bank of LEDs- this time using a yellow LED, and daisy chaining it to the prior LED bank, in series..

My thought was, it would simply cause both banks of LEDs to blink.

But I am finding that it is either one or the other. Both banks will not blink at the same time.

I am sure there is some sort of principle I am not understanding, and violating. Can someone give me a clue?

Thank-you

 

[bertus]

Hello,

As always, when you have a question, post the schematic.
Can you draw a schematic of the set-up?

Bertus

 

[SparkyCal]

I can't draw a schematic yet, but this is what i can do. Here is the circuit I am working withsee attached. )

I also hand drew the LED banks and their connections.

 

[bertus]

Hello,

Do you have the specifications of the leds?
When the leds do not need serial resistors, aka 12 Volt leds, they should light at the same time.
It is not a good idee to put classic leds parallel.
A classic blue led would need 3 to 3.5 Volts to work.
A classic yellow led would need 2 to 2,5 Volts to work.

Bertus

 

[SparkyCal]

Yes I do Bertus. The blue LEDs are 3.oV-3,4V 20mA. the yellow are 1.8V-2.4V 30 mA.

 

[bertus]

Hello,

When putting leds in parallel, each led must have its own current limiting resistor.
When the supply voltage is high enough, you can put several leds in series with one resistor.

You might want to read this thread made by Wendy on the AAC:
https://forum.allaboutcircuits.com/threads/leds-555s-flashers-and-light-chasers.19075/

Attached you will find a led color chart with some typical forward voltages.

Bertus

 

[SparkyCal]

Thank-you. i think you nailed the problem. I failed to realize I was working these banks of LE Ds in parallel. I had assumed, it was i. series. But your observation makes perfect sense. A few solutions are now becoming apparent. Thank-yopu

 

[Bluejets]

Just be aware the 555 has a maximum current limit of around 200mA.

 

[SparkyCal]

Thanks. I have reconsidered this and decided not to introduce a second bank of LEDS. But I learned something from this, do thanks for that,

 

[Nanren888]

BTW, did you have one resistor per LED bank, or one shared?

each led must have its own current limiting resistor.

As mentioned, one per LED is best.

 

[Bluejets]

Thanks. I have reconsidered this and decided not to introduce a second bank of LEDS. But I learned something from this, do thanks for that,

When you get in to high power LED's , constant current /voltage drivers can be an advantage.

 

[Martaine2005]

LEDs can be connected either series, parallel or a combination of both depending on the circuit and voltage available.
There is a great resource section on this forum here , that will explain all you need to know about LEDs.

Martin

 

[Martaine2005]

I failed to realize I was working these banks of LE Ds in parallel. I had assumed, it was i. series.

BTW, top is series and bottom is parallel.
No need to ever ‘assume’ again.

Martin

 

[Audioguru]

My cheap Chinese flashlight has 24 white LEDs in parallel and it works fine. All the LEDs must have been tested and grouped into groups having only one matching forward voltage. The forward voltage is about 3.2V and if a few 2V red LEDs were additionally in parallel then the red ones would light up VERY brightly and the white LEDs would not conduct and produce no light.