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Sequential fading LEDs. Power / intensity loss by the end of the string. How to make all LEDs the same brightness? Answered

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Trying to build a sequential fade on when power is applied and fade off when power is removed LED circuit. I have problems with power loss by the end of the LED string. 
The current layout has 4 LEDs that will fade on one at a time until all 4 LEDs are lit and then the fade off in reverse order.

My original idea came from osgeld's No CPU / MCU led pulse-fade circuit. 

Any ideas on how to keep the power to the LEDs consistent from the first to the last?

The idea is not needing to program any chips.


Once I/we have figured out how to complete this circuit as desired, I will post it as my first Instructable.

19 Replies

user
Re-design (author)2011-03-08

T3,4,5 are not turning fully. T2 is the only transistor turning on fully.

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user
pinhead1984 (author)Re-design2011-03-08

How would you correct this flaw in the circuit?

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user
Re-design (author)pinhead19842011-03-09

There are two thing I would try.

#1. is the most difficult. Since 2n2222 are amps they are not turning on fully. You could change the transistors for switching transistors that would turn fully on but then the circuit might not work properly. They might all go on at once.

#2. is the method I'd try first. Measure the voltage to led 2 and calculate the res. for R5 to get it to full voltage, change it and that will probably fix it. Now measure the voltage to led 3 and change R6 and do the same for the last set. You can't change them all at once since changing the one before it will change the next voltage. This should work.

Good luck.

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user
pinhead1984 (author)Re-design2011-03-10

Do you think that this diagram may solve the problems and work? I can control the fade on and fade off times in this circuit.

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user
Re-design (author)Re-design2011-03-10

or maybe all it would take is to move the resistors between the led and the wire that leads to the next transistor.

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user
lemonie (author)2011-03-08


I don't know what you mean by "I have problems with power loss by the end of the LED string."
How long are the wires between the LEDs?

L

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pinhead1984 (author)lemonie2011-03-08

The circuit is on a project board at this time. Each one of the LEDs on the diagram is 2 pre-manufactured sets of 3 LEDs with their own resistor per set of 3 (3 LEDs in series 2 set in parallel).

The voltage reading to the base of each transistor is as follows:
T1: 7.9v
T2: 7.3v
T3: 6.6v
T4: 5.9

The emitter voltages are:
T1: 7.3v
T2: 6.6v
T3: 5.9v
T4: 5.3v

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user
lemonie (author)pinhead19842011-03-09


Isn't it supposed to be stacked that way?
You cut the power and they go off in sequence?
You've not said what it isn't doing that it should be doing very clearly.

L

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user
pinhead1984 (author)pinhead19842011-03-08

Sorry, its T2, T3 ect...
Not T1

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user
steveastrouk (author)2011-03-08

Are you actually seeing a ripple effect ? ...because I can't see how.

Steve

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user

I was pretty sure your circuit wouldn't work, and I can see exactly why. I also don't think t1 is doing anything.

First, put the LEDs in the collector of each transistor, with its dropper resistor.

Put a resistor from the collector to the base of the next transistor.

Put a capacitor (100uF ?) from base to ground on each transistor.

Steve

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pinhead1984 (author)steveastrouk2011-03-09

There is no ripple effect. All of the LEDs are steady once they are on.

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user
steveastrouk (author)2011-03-09

DOES it "ripple" at all ?

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user
pinhead1984 (author)steveastrouk2011-03-09

No, there is no ripple in the circuit. All LEDs are on and steady.

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user
oreodjr (author)2011-03-08

its all in the resistorsssss~~~

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user
pinhead1984 (author)oreodjr2011-03-08

Please clarify. That is not a helpful answer

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user
Re-design (author)2011-03-08

Is you power supply strong enough to run 5 transistors, 4 leds and charge the cap all at the same time?

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user
pinhead1984 (author)Re-design2011-03-08

Power source is a 12v 10A variable power supply (and yes, its set for 12v and set at 10A) Installation of this circuit will be in a car

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