# Question on LED flasher.

#### reno12469

Joined Jan 17, 2009
47
I have a schematic but i dont know how to get it up here because its in paint. I was wondering if it would work or not. So if anyone can help me on how to put it up it would be nice.

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#### Audioguru

Joined Dec 20, 2007
11,249
Save it as a PNG file type and attach it with your reply here.
You will see the manage Attachements box in Go Advanced then you Browse for the schematic and Upload it. Then Submit Reply.

#### reno12469

Joined Jan 17, 2009
47
OK, here it is. For the blue they have a forward voltage of 3.2V and a max of 4.0V and operate at 20mA. The red have a forward voltage of 2.1V and a max of 2.6V and operate at 20mA. I was wondering if i could also use a 556 instead of a 555 and hook two sets of white LEDs. They have the same spec as the blue ones.

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#### SgtWookie

Joined Jul 17, 2007
22,210
Do you know that your voltage supplies are connected incorrectly?
You have the negative voltage outputs connected to the positive rails.
You don't have the positive voltage outputs connected to anything.

Are you planning on using this in a vehicle? If you're in law enforcement, blue lights are OK, but not for ordinary civilian use on any public roads.

Looks like you haven't calculated your current limiting resistors properly for the blue LEDs - unless 3.2v is the minimum and 4.0 is the maximum? You want to use the typical Vf, like this:
R = (VSupply - (total Vf of LEDs))/Desired Current
If your typical Vf is 3.6v @ 20mA, then:
R = (13.7 - (3 * 3.6))/20mA = (13.7 - 10.8) / 0.02A = 2.9/0.02 = 145 Ohms.
If the red LED's typical Vf is 2.3 @20mA, the resistors should be 340 Ohms.

If you're going to use them in an automobile, that'll complicate things a tad. You will need to use a voltage regulator, as an automotive electrical system may vary in voltage from as low as 11.4v (dead battery) to nearly 15v just after starting. Using a regulator will take away from the maximum voltage available, so the resistors will need to be re-calculated anyway.

#### reno12469

Joined Jan 17, 2009
47
Yea I'm new to making circuit diagrams. This will be for a car. I am not in law enforcement and i know that they are illegal to have but there just for show. I have attached the data sheet for the LEDs. Is there a voltage regulator that will change with the Volts to always keep it at 12V? Another thing is that i want to just splice the cigarette lighter in the vehicle for power. Is that always at 12V and never higher?

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#### Metalfan1185

Joined Sep 12, 2008
161
Voltage in a car is not regulated, so you will get from 11.5 to 14.1V from the cigarette lighter.

take a look at the LM7812 Positive Voltage regulator. It's really easy to use.

I do automotive electronics myself, be sure to take current measurements on the LED series segments and make sure the resistor is rated for the correct wattage. and a value that corrects the LED's Forward Voltage. they may get a little hot too.

I would also drive each cluster of LED's with it's own transistor or MOSFET, the 555 doesn't offer too much current off of pin 3.

One last thing...to be safe, wherever you connect any homebrew circuits into the Auto's + battery supply, use a fuse, (maybe 1/2 A to 1A in your case) do not rely on the car's fuses to stop damages to your car and or circuit.

If you want to see a few auto electronics things that i have done, check out
www.myspace.com/customautoelectronics

if you have any questions with anything i'd be happy to help!

#### reno12469

Joined Jan 17, 2009
47
Can you give me a schematic. Because im completely lost on what your saying.

#### reno12469

Joined Jan 17, 2009
47
What type of LEDs do you think i should buy? I want them to be pretty bright but still have the through hole design.

#### Audioguru

Joined Dec 20, 2007
11,249
The cheap LEDs sold on E-Bay are dim old chips in a tightly focussed case making a narrow angle so they appear as bright as modern ones whan they are on-axis. They cannot be seen off-axis.
Modern bright LEDs are wide angle.

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#### reno12469

Joined Jan 17, 2009
47
What would be a good angle for this project? And im a little confused. What determines how bright an LED is? Is it the luminous intensity or is it the angle?

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#### Wendy

Joined Mar 24, 2008
22,155
It is actually both. Lumans give you the total light output, but the apparent brightness is increased by reducing the angle it is projected, so the light generated covers a smaller ground. It can be pretty useful actually, a way of projecting a beam of light without using a laser, useful for detectors and whatnot.