LED light bar help

[williamsjp2004]

I'm trying to build an LED light bar that runs off of 12V that I can turn a potentiometer to control the intensity. That's the easy part. The part that I'm running in to problems with is that I would like it to fade in one by one.

When LED 1 is lit to about 3 volts (I will be using 3 volts as my maximum for the LEDs, all LEDs will be the same), I would like LED 2 to begin lighting. After LED 2 is lit, LED 3 begins, and so on...

The only thing I have been able to figure out is connecting 12V to a pot. to a current limiting resistor, from the limiting resistor to an LED, from LED to BOTH the next LED and to a resistor connected to ground. The problem is, this works up to about 3 LEDs, then the rest (of a total of 7) don't light and if I apply enough power, the first LED fails under the load or course.

I'm hoping I explained that well enough. Basically I would kind of like to have a single equalizer bar that is controlled by a pot. instead of by sound. I'm trying to get as basic as possible but do know how to read schematics and can put together any circuit not using personally coded ICs.

Thank you in advance for the advice.

 

[Gryd3]

I'm trying to build an LED light bar that runs off of 12V that I can turn a potentiometer to control the intensity. That's the easy part. The part that I'm running in to problems with is that I would like it to fade in one by one.

When LED 1 is lit to about 3 volts (I will be using 3 volts as my maximum for the LEDs, all LEDs will be the same), I would like LED 2 to begin lighting. After LED 2 is lit, LED 3 begins, and so on...

The only thing I have been able to figure out is connecting 12V to a pot. to a current limiting resistor, from the limiting resistor to an LED, from LED to BOTH the next LED and to a resistor connected to ground. The problem is, this works up to about 3 LEDs, then the rest (of a total of 7) don't light and if I apply enough power, the first LED fails under the load or course.

I'm hoping I explained that well enough. Basically I would kind of like to have a single equalizer bar that is controlled by a pot. instead of by sound. I'm trying to get as basic as possible but do know how to read schematics and can put together any circuit not using personally coded ICs.

Thank you in advance for the advice.

You're lucky the Potentiometer didn't begin to smoke.
Your solution may require a microcontroller, or a small collection of other components to properly drive each LED.
LED's are unique creatures that like to take... you need a resistor to limit the current to a safe level. Your current setup increases the current through the LED until it dies...

 

[williamsjp2004]

I forgot to mention I modeled everything virtually and on paper first as to avoid burning up any physical components.

That's what I was afraid of. It's just going to take a little more work is all. I was going to use this as an introductory project to a much more complicated setup down the road and I wanted to start with as few components as possible.

I guess it's time to brush up on simi conductor/MC again.

Thank you for the reply!

 

[Gryd3]

You may be able to build something by using transistors.
If each transistor is baised a little differently they will turn on at different rates. The tricky part will be biasing them properly, and making sure that they will handle the LEDs you plan to use. (As they fade on, the transistors will operate in a linear region and generate some heat...)

 

[Scotophor]

I'd use an array of comparators, and a string of resistors for reference voltages.

 

[Gryd3]

I'd use an array of comparators, and a string of resistors for reference voltages.

Or an LM3914.. but this would not allow the LED's to 'fade' on.
It would cut down on component count by quite a bit though.

 

[Arouse1973]

You may be able to build something by using transistors.
If each transistor is baised a little differently they will turn on at different rates. The tricky part will be biasing them properly, and making sure that they will handle the LEDs you plan to use. (As they fade on, the transistors will operate in a linear region and generate some heat...)

What about driving them from an emitter follower with an RC network on the base to fade them in. This might work.
Adam

 

[Scotophor]

Ooh, new brainstorm... do you need each individual LED to have infinite brightness control, and once it's fully lit, the next one begins to light? Or would it be acceptable for each LED to have just a few discrete brightness steps? The LM3914 bargraph driver idea from Gryd3 could be extended by cascading drivers so that the total number of outputs is some multiple of the total number of LEDs. By setting the output currents low and connecting multiple outputs to each LED, you could get several levels per LED. For example, using 36 outputs to your 12 LEDs would give 3 brightness levels on each LED.