flashing leds

Discussion in 'The Projects Forum' started by dd1313, May 23, 2010.

1. dd1313 Thread Starter New Member

May 23, 2010
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Hello everyone,

This is my first post.I am helping my grade 6 daughter with a science
project.I am also new to electronics.What she wants to create is a toy
(that is her theme).She must use just basic stuff, like LED,battery,resistors
nothing like 555 etc,

She wants to create a stage, like the ones the ladies model on.And she will
place 2 dolls on it.Now the outline of the stage will have flashing LEDs

connecting the LEDs in paralell is the solution and then connecting them
to a resistor and then to a battery.

I have researched that we should ask the electronics store for flashing LEDs.

Thanks
Devan

2. Bychon Member

Mar 12, 2010
469
41
You seem to have all your ideas correct, to the point that I have trouble finding that you are asking a question. What can I say? Buy the blinking LEDs and start calculating the resistors...or buy the blinking LEDs and ask how to calculate resistors based on what you've bought.

3. dd1313 Thread Starter New Member

May 23, 2010
14
0
Thank you,

If they are blinking LEDs, they don't have to be in paralell do they ?

And how do we calculate the resistance if we have the LEDs,are all LEDs the same

Thanks
Devan

4. Bychon Member

Mar 12, 2010
469
41
Blinking leds will have to be in parallel, otherwise, the first one that goes off will stop all the others.

How do you calculate the resistance if you don't have any LEDs? They are not all the same. You need the LEDs specifications and the voltage you will be using to do the calculations.

(Power voltage minus the LED voltage) divide by the current needed by the LED = resistance.

5. Bychon Member

Mar 12, 2010
469
41
These are available in 3 colors from www.mouser.com

They don't need any resistors.

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6. dd1313 Thread Starter New Member

May 23, 2010
14
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i truly appreciate the guidance.I will have to checl tomorrow at the store for the ones that I can get.We will be using a 9V battery .How many LEDs can we use please.

Thank you
Devan

7. Markd77 Senior Member

Sep 7, 2009
2,803
596
9V pp3 batteries have fairly poor capacities so I'd keep it low. 4 or 5 of those Mouser ones would probably drain a battery in a couple of hours.

8. Wendy Moderator

Mar 24, 2008
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Modern LEDs can be hazardous to look directly into due to their brightness, so some caution is required.

Why no 555's? I assume other logic isn't used either. For simplicity?

9. k7elp60 AAC Fanatic!

Nov 4, 2008
555
106
Most blinking LED's do not require resistors in series with them when operated on a 9V battery. You can even connect a different color standard LED in series with blinking LED's and both LED's in the string will blink at the same time. Radio Shack as a several blinking LED's. I would think 10 or 12 blinking LED's would last quite some time on a standard 9V battery, as I have a small pumpkin for halloween that has two blinking LED's that lasts for over a week on one 9V battery.

Apr 5, 2008
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11. dd1313 Thread Starter New Member

May 23, 2010
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Thanks..

do you know what they are using here do hold the resistor

http://www.hobbyprojecten.nl/afbeeldingen/spijker.jpg

DD

12. dd1313 Thread Starter New Member

May 23, 2010
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Yes, it's just to test they know how to apply circuits in practice.
Nothing fancy.

Apr 5, 2008
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Hello,

The resistor is held at place using a copper nail.
The advantage of copper nails is, they can be soldered.

Bertus

14. Wendy Moderator

Mar 24, 2008
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I'm confused a little, you can use transistors but not 555's? Are you wanting runway lights, where they sweep down the strip, or just flashers?

15. dd1313 Thread Starter New Member

May 23, 2010
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just flashing lights

16. dd1313 Thread Starter New Member

May 23, 2010
14
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can you connect paralell circuits to form bigger paralell circuits

Thanks
Devan

17. Wendy Moderator

Mar 24, 2008
21,425
2,949
Reading the data (no sheet, just word of mouth) for this Radio Shack Blinking LED it has a Vf of 3-3.8V, so for a 12V power supply at 20ma you would need a 390Ω resistor.

You can put other non blinking LEDs in series and reduce the resistance to get them to blink in time, but the power supply dictates how many. For 12V it is around 4 (including the blinking), for 24VDC it is around 8. LED color affects this, the units we're talking about is red. Other colors drop more voltage. LEDs are current devices, you can not eliminate the resistor in spite of what has been said by others, unless the data sheet specifically says you can (a major exception).

Just for the record, Radio Shack is not the best place to buy parts. They have a 100% to 1000% mark up compared to most vendors. If you are interested we can point you to some better deals.

There is no way to sync it with other LEDs without additional electronics, with simplicity comes major limitations. If you're willing to use transistors, 555s or other circuitry you can have real runway lights, but not with LEDs only, they will be at their own rate and pretty random.

I have an article for other special effects if you change your mind.

LEDs, 555s, Flashers, and Light Chasers

I've made true runway lights with some simple circuits, something like this.

Last edited: May 24, 2010