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Help with flashing LED circuit design. Answered

Hello, I was wondering if some could help me with a circuit design. Designing is my weak point, so apologies in advance if it is a simple question.

Basically, there will be 9 LED's in total, 3 in each row. It will be powered by a 9v battery. The LED's are 2.2v50mA.

So I want the 3 LED's in Row 1 to illuminate.

Then Row 1, de-luminate fully, then Row 2 to illuminate straight after.

Then Row 2, de-luminate fully, then Row 3 to illuminate straight after.

Then start over again, so it's basically a sequence of 1,2,3,1,2,3,1,2,3 etc.

From what I understand a 555timer is required? 

I'm looking to do this as cheap as possible Any help or guidance would be appreciated.

Thanks!

5 Replies

user
LiquidLightning (author)2011-01-14

I'm not sure if this would work, but why not just put a capacitor in front of each line and wire in pararell?

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user

Won't work, not least because the battery is the wrong way round.

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user

I drew and thought of it in haste. Mah bad.

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user
AndyGadget (author)2011-01-15


A 555 timer on it's own would only give you 2 of the strings flashing alternately. 
To get three flashing in sequence you could use a 4017 decade counter IC.  There's some information on a the chip and a circuit you could base your design on HERE.  (You would also need to build a clock circuit like the one they mention to clock the circuit.  You could use a pot to control the speed.)
You would have your LED strings connected to the first three outputs of the 4017 and the fourth output would go to the RESET pin to re-start the count.
If you were driving the LEDs at the full 50mA you would need transistors at the bottom end of each LED string, and you would need to drive the circuit at the full 9V to get over the LED voltage drops.

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LiquidLightning (author)2011-01-14

Oh wait, nvm, that would have each line stay lit even as the next lights.

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