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help with a basic 5 LED circuit

DevilWAH

Jan 18, 2016
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Hi,

First of all electronics are not my thing, biology or networking and I am at home, but apart from distance memories from GCSE's I am coming back to electronics blind and would really appreciate some help.

I have printed out a rocket on a 3D printer and now would like to place some LED's inside to illuminate it. 3 of these will be static blue, and two will flash yellow and red alternatively (pretend flames from motor).

I want to run it from 2 X 1.5V AA batteries as I already have some 2.9v blue LED's (10ma). I thought 2X AA would work OK

First of all I tried to cacluate what resistors I should use and it worked out at 12ohms, is this correct do i need to put a resistor in? And in parallel I would need one resister per LED. So I think this bit is OK.

Next I want to have the red and yellow LED flash alternatively but quite rapidly so it flickers more than an on off effect. What is a good circuit to use to achieve this, the words "flip flop" pop to mind but I am not sure this is the best method.

I have drawn up a very basic first attempt, (with out the oscillator part which would run LED's 4 and 5. The idea would be that when the circuit is turned on LED's 1,2 and 3 light up. when the button is pressed then led's 4 and 5 flicker simulating the engines coming on.

Any help is appreciated.

Aaron
 

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Gryd3

Jun 25, 2014
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Hi,

First of all electronics are not my thing, biology or networking and I am at home, but apart from distance memories from GCSE's I am coming back to electronics blind and would really appreciate some help.

I have printed out a rocket on a 3D printer and now would like to place some LED's inside to illuminate it. 3 of these will be static blue, and two will flash yellow and red alternatively (pretend flames from motor).

I want to run it from 2 X 1.5V AA batteries as I already have some 2.9v blue LED's (10ma). I thought 2X AA would work OK

First of all I tried to cacluate what resistors I should use and it worked out at 12ohms, is this correct do i need to put a resistor in? And in parallel I would need one resister per LED. So I think this bit is OK.

Next I want to have the red and yellow LED flash alternatively but quite rapidly so it flickers more than an on off effect. What is a good circuit to use to achieve this, the words "flip flop" pop to mind but I am not sure this is the best method.

I have drawn up a very basic first attempt, (with out the oscillator part which would run LED's 4 and 5. The idea would be that when the circuit is turned on LED's 1,2 and 3 light up. when the button is pressed then led's 4 and 5 flicker simulating the engines coming on.

Any help is appreciated.

Aaron
2x AA batteries might be a tiny bit low with Blue LEDs as they batteries start to wear.
Anyway, I would suggest you look into random number generator or 'candle flicker' type circuits. There are some tricks you can use to keep your circuit small. Additionally, you can rely on a small 8-pin microntroller (PIC, AVR, or similar) and program a simple pattern for the LEDs.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Well, you have the resistors in all the right places. I agree with @Gryd3 that two AA cells probably won't hack it for long. Three (4.5 V) or four (6 V) would be my minimum, sizing the resistors accordingly. I would scale those up to at least "D" size if you expect the display to run very long. Two or three cells would be enough to run a PIC and the simplest one will do, such as a PIC10F100, -102, 104, or 106. Go to the Microchip website and download the datasheet. Purchase a few of these (they are dirt cheap) in the 8-in DIP package instead of the 6-pin SO-23 surface mount package. You will also need a PICKit 3 (or PICKit 2) programming pod, which interfaces between a USB connection on a PC and the PIC, but can be (should be) removed after the PIC's non-volatile memory is programmed. Learn to program the PIC, hook up some wires from the LEDs to the four output ports and... Voila! A pretty fancy display!

If the PIC microprocessor solution appeals to you, post back and someone here will probably upload a schematic. This literally ain't "rocket science" and it will be a lot of fun. Well, maybe in your case the project is sort of rocket science... rocket model illumination science anyway.

And welcome to Electronics Point @DevilWAH!

Hop
 

duke37

Jan 9, 2011
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A 555 is not my thing but here it can be used to flash leds alternativly. Make it run as a flip/flop and place your reds between output and ground and your yellows between positive and output. The 555 can supply sufficient output without amplification.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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@duke37 The 555 was my first thought too, but it doesn't provide the pseudo-randomness of a flickering rocket exhaust so I discarded the idea. A long ring counter (maybe sixty-four bits long) made with discrete integraded circuits, with taps located at "random" locations, the taps driving the LEDs, might produce the desired effect quite easily. The ring counter needs to be loaded with a "seed" bit pattern first, hence it really isn't random at all, but in appearance it might be "good enuf" for a flickering rocket exhaust display. Cheap and simple too. Can be clocked with your 555.:D
 

Colin Mitchell

Aug 31, 2014
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BikeFlasher-Amazing-1.gif
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Nice circuit, Colin, for powering up white or blue LEDs, but the problem we are considering is how to make the red and yellow LEDs flicker like a lit candle.
 

Colin Mitchell

Aug 31, 2014
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" but the problem we are considering is how to make the red and yellow LEDs flicker like a lit candle."

If you could understand how a circuit works, you could see that it does that.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Yep, sure it will. Two relaxation oscillators running independently should do the trick. Stick in whatever color LEDs you want: red, yellow, green, blue, even white. Elegant solution, Colin.
 

Colin Mitchell

Aug 31, 2014
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I would not really call it a relaxation oscillator because this term just refers to the circuit changing from one state to another.
It is much more complex than that.
Firstly the circuit has a transformer and it works on flyback to produce about 30v. This voltage is clipped at 7v to illuminate the two LEDs.
It must drive two or more LEDs to achieve at least 7v and that's why no-one has designed this circuit before.
During this time the 10u is charging via the energy coming out the feedback winding when the transistor is being turned ON. And then it provides the turn-ON current for the transistor for the next cycle. A point is arrived when the 10u is charged so much that the charging current is insufficient to start the next cycle. The transistor does not turn on and the 10u is discharged via the 100k. This is the OFF time. It discharges to a point where the base current is sufficient to start the next cycle. It will produce quite a number of cycles before it: "chokes itself to death." And it stops working.
It is commonly known as a JOULE THIEF but its technical name is FLYBACK OSCILLATOR.
 
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