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Powering LEDs Question

Discussion in 'LEDs and Optoelectronics' started by SparkyCal, Jun 7, 2020.

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  1. SparkyCal

    SparkyCal

    831
    31
    Mar 11, 2020
    Below is a picture of a circuit I am building on a PCB board. I could not figure out how to make the picture bigger, so if it is difficult to see, you can see it full size at. :32 here:


    You will note that the schematic calls for a number of individual 560R resistors that are attached to pin 3 of the 555 timer, and then attached to a LED ( one LED per resistor).

    I am looking for advice on how to physically wire/solder this.

    Do I solder one wire to Pin 3, and then attach one side of each resistor to that wire? I am thinking that could be quite messy because then I would have 12 resistor ends, all connecting to that single wire coming from Pin 3 of the 555 Timer.

    I am sure there must be a better way, but I've never done this before. I know that the circuit boards I bought came with break off header pins. Will those help?

    Thank-you
     

    Attached Files:

  2. ramussons

    ramussons

    385
    73
    Jun 10, 2014
    Yes, that is how it is done, even is it is a PCB. Or do you feel that connecting 12 resistors to a single pin is easier? And please notice that the "gnd" has more than 12 connections.
    The LED's with their Resistors are strung exactly like in the schematic, though their physical layout may be shaped like the heart.
     
  3. bertus

    bertus Moderator

    2,071
    781
    Nov 8, 2019
    Hello,

    The circuit will draw a current of 12 X ledcurrent.
    When using 6 X 2 leds in series , the used current can be half, and prolong the battery life.

    Here is a larger picture of the schematic from that video:

    ledheart.png

    Click on the picture to show it even larger.

    Bertus
     
  4. Bluejets

    Bluejets

    5,043
    1,053
    Oct 5, 2014
    Even could go 2 legs in parallel, 6 leds in series and a 100R resistor in each of the two legs.

    Original circuit would exceed the current rating (200mA) of the 555 (216mA)
     
    hevans1944 likes this.
  5. bertus

    bertus Moderator

    2,071
    781
    Nov 8, 2019
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,713
    2,719
    Nov 17, 2011
    The suggestion is not to have all LEDs in parallel, rather build 2 strings of 6 LEDs in series, each string with 1 resistor, both strings in parallel:
    upload_2020-6-7_15-7-1.png
    Perfectly legitimate and saves power: power is used to illuminate the LEDs, not to heat the resistors.
     
    hevans1944 and davenn like this.
  7. bertus

    bertus Moderator

    2,071
    781
    Nov 8, 2019
    That will likely not work, as the output voltage of the 555 will be to low.
    The output voltage is about 2 volts lower as the supply voltage.
    The original circuit uses a current of about 15 mA for each led.
    Perhaps make 3 strings of 4 leds with a resistor of 120 Ohms in each string, wich will result in about 17 mA in each string.

    Bertus
     
    hevans1944 likes this.
  8. SparkyCal

    SparkyCal

    831
    31
    Mar 11, 2020
    I think I will stick to the original schematic, only because I don't see hsving to leave this circuit on for a lomng period of tiem, thus i am not overly concerned about battery drain.

    I have a question though. If in the diagram, I decided to twist together all the resistor leads, and then connect the twisted together end, to Pin 3, woukd this screw everything up. It is necessary that each resistor travel to the Pin3 lead on its own? I am thinking it would screw everything up because it may change the value of the resistors to be the addition of all the resistances. True?
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    11,713
    2,719
    Nov 17, 2011
    No, definitely not. In this circuit it makes no difference. The resistance of the wire connecting the resistors to pin 3 is negligible compared to the resistances used (unless you use ultra-thin wire ;)).

    Just for future reference: There are circumstances where it matters how you make the connection. Ususally when very high frequencies or very steep signal edges are involved. This is off no concern here.
     
  10. SparkyCal

    SparkyCal

    831
    31
    Mar 11, 2020
    I was not concerned about the wire. I was wondering. If the resistors were bunched into one connecting point, could they form a super resistor or will they all maintain their same resistance values
     
  11. bertus

    bertus Moderator

    2,071
    781
    Nov 8, 2019
    Hello,

    Looking at the back of the PCB in the video, each resistor is connected to one led:

    555 heart back.png

    Bertus
     
    hevans1944 likes this.
  12. Harald Kapp

    Harald Kapp Moderator Moderator

    11,713
    2,719
    Nov 17, 2011
    Why would the resistance of a component change depending on how it is connected?
    upload_2020-6-9_6-41-16.png
    In this example each resistor has an (arbitrary) resistance "R", regardless of the connection.



    A different story is a connection like this one:
    upload_2020-6-9_6-42-40.png
    Here the 3 resistors are connected on both ends, a parallel connection. While each single resistor still has a resistance of "R" (remember it doesn't change with the type of connection), the total circuit with 3 resistors in parallel has a resistance of 1/3 × R.

    Whereas in this connection
    upload_2020-6-9_6-48-24.png
    The total of the resistance is 3 × R.

    Read more about series and parallel connection of resistors e.g. here.
     
    hevans1944 and bertus like this.
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