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# Help needed in powering 500 flashing led.

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#### RaySoul

##### New Member
Hi dudes, currently i am working on a project which will require to power up 500 white led. The project is just to let the 250 led flash alternately with another 250 led.

I have try using the 555 timer to control, but the Power supply i am supplying is 16 x AA" battery which will add up to 24v? I added in so much battery is because, LED is a current component. So in order to light them up, i have to supply enough current for all of them?

But now the problem comes in. the IC 555 timer can only take up to 15v max.

The circuit i am currently using is this LED Flasher Using 555 IC | Free Circuit Diagram

I have tot of another method is to use 2 of the circuit(above). but the flashing wouldn't be alternately, due to the time different i guess.

Can any dude here help me with this? Much appreciation.

A single LED has a forward voltage drop of between 2 to 3.5V, depending on color. To power 250 of them in a single series string, it would take a minimum of ~500V, so obviously, you have to wire small groups in series where each group shares one current limiting resistor, and then wire many groups in parallel.

This means you can choose an operating voltage which powers a group, like 15V which might power 5ea 2.2V Leds, leaving 4V across the current limiting resistor. Obviously, it would take 25 groups in parallel to get 250 Leds.

Assuming you plan to operate the groups at 20mA, this means that the total current through 25 groups would be 1/2A. At 1/2A, your proposed AA batteries would last about 1 min!!! Try a 12V car battery.

Last edited:
Multi LED flasher thingy schematic

I knocked up a quick schematic of what you will need to do. This shows 90 white leds connected to 6 of the 12 ports of a PIC16F676, which drives logic level mosfets.. It's all easily scalable to use any number of leds, but you should get the basic idea.
Writing the code for the pic would be a simple matter, and shouldn't take more than about an hour.
The unused ports have been tied to ground, but could be assigned to push buttons to allow speeding up of the flashing, resetting etc etc...

I haven't tried this schematic, but it's really simple.

#### Attachments

• flasher thingy.GIF
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Try this wizard.

Ron

Wow..Thank for all replies..Really appreciated it..

But as i have connect all the led in parallel, is there any bad side of it?

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