Connect with us

A Funny Thing Happened on the way to this circuit

Discussion in 'General Electronics Discussion' started by SparkyCal, May 18, 2020.

Scroll to continue with content
  1. SparkyCal

    SparkyCal

    362
    14
    Mar 11, 2020
    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
     
  2. bertus

    bertus Moderator

    1,150
    436
    Nov 8, 2019
    Hello,

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

    Bertus
     
    narkeleptk likes this.
  3. SparkyCal

    SparkyCal

    362
    14
    Mar 11, 2020
    I can't draw a schematic yet, but this is what i can do. Here is the circuit I am working with:(see attached. )

    I also hand drew the LED banks and their connections.
     

    Attached Files:

  4. bertus

    bertus Moderator

    1,150
    436
    Nov 8, 2019
    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
     
  5. SparkyCal

    SparkyCal

    362
    14
    Mar 11, 2020
    Yes I do Bertus. The blue LEDs are 3.oV-3,4V 20mA. the yellow are 1.8V-2.4V 30 mA.
     
  6. bertus

    bertus Moderator

    1,150
    436
    Nov 8, 2019

    Attached Files:

  7. SparkyCal

    SparkyCal

    362
    14
    Mar 11, 2020
    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
     
  8. Bluejets

    Bluejets

    4,258
    907
    Oct 5, 2014
    Just be aware the 555 has a maximum current limit of around 200mA.
     
  9. SparkyCal

    SparkyCal

    362
    14
    Mar 11, 2020
    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,
     
  10. Nanren888

    Nanren888

    337
    83
    Nov 8, 2015
    BTW, did you have one resistor per LED bank, or one shared?

    As mentioned, one per LED is best.
     
  11. Bluejets

    Bluejets

    4,258
    907
    Oct 5, 2014
    When you get in to high power LED's , constant current /voltage drivers can be an advantage.

     
  12. Martaine2005

    Martaine2005

    2,967
    817
    May 12, 2015
    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
     
  13. Martaine2005

    Martaine2005

    2,967
    817
    May 12, 2015
    upload_2020-5-19_8-33-1.jpeg
    BTW, top is series and bottom is parallel.
    No need to ever ‘assume’ again.

    Martin
     

    Attached Files:

  14. Audioguru

    Audioguru

    2,985
    668
    Sep 24, 2016
    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.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-