Maker Pro
Maker Pro

Powering LEDs Question

SparkyCal

Mar 11, 2020
846
Joined
Mar 11, 2020
Messages
846
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
 

Attachments

  • Screen Shot 2020-06-07 at 12.23.06 AM.png
    Screen Shot 2020-06-07 at 12.23.06 AM.png
    128.9 KB · Views: 4

ramussons

Jun 10, 2014
441
Joined
Jun 10, 2014
Messages
441
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.
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.
 

bertus

Moderator
Nov 8, 2019
2,642
Joined
Nov 8, 2019
Messages
2,642
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
 

Bluejets

Oct 5, 2014
5,884
Joined
Oct 5, 2014
Messages
5,884
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)
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,615
Joined
Nov 17, 2011
Messages
12,615
It is not wise to put several leds direct parallel:
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.
 

bertus

Moderator
Nov 8, 2019
2,642
Joined
Nov 8, 2019
Messages
2,642
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:

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
 

SparkyCal

Mar 11, 2020
846
Joined
Mar 11, 2020
Messages
846
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?
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,615
Joined
Nov 17, 2011
Messages
12,615
It is necessary that each resistor travel to the Pin3 lead on its own?
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.
 

SparkyCal

Mar 11, 2020
846
Joined
Mar 11, 2020
Messages
846
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
 

bertus

Moderator
Nov 8, 2019
2,642
Joined
Nov 8, 2019
Messages
2,642
Hello,

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

555 heart back.png

Bertus
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,615
Joined
Nov 17, 2011
Messages
12,615
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
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.
 
Top