Multiple Led's on each channel of a chaser circuit (4017)?

T

TMan1876

Limp Gawd
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Jul 12, 2006
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I am looking to built a fairly large lighting system for a project that I am planning. I have found diagrams for LED chaser circuits that could be expanded to provide the number of channels that I desire (24).

The only problem is that I would want to connect 4 LEDs to each channel.

What would I have to do to make this work? Is there a heavy duty version of the 4017 IC that could drive 4 LEDs per channel? Or would I have to have some kind of amplifier for each group? Or something entirely different?

We are looking at 96 LEDs total, so it will be quite a project no matter what I do.

Thanks in advance for the help, I'll try to get a diagram up of what I am thinking of when I get a chance.
 
You can use each 4017 output to switch a small NPN transistor such as a 2N3904 (200mA) or 2N2222 (600mA); for a compact system the ULN2803A IC could be useful, an 8-channel darlington chip that will connect straight to the 4017's and give all the current amplification you need.

You can also run your LEDs in series to reduce the current compared to a parallel set-up; a 12V supply will run four 2V LEDs with a margin for the current-setting resistor.
 
I would use some cheap transistors or FETs. Just connect the output to the gate of the FET, with a pulldown or pull-up resistor as necessary.
 
I was planning on running them as two sets of two LEDs in series connected in parallel, if that makes any sense.

So there would be a current limiting resistor, and then it would split into two sets of two LED's in series.

I don't know if that would be enough, because they would still be pulling 40 mA on each channel.

I like the idea of an 8 channel amp that I could use to amplify all of the outputs in one package...

That way I could just use any old 4017, and just have one of the 2803's for each one. This is sounding more doable. I need to get my sim program going so I can test this out.
 
The 4017 won't reliably drive four LEDs. So you will need to use a 2803 type chip which will invert the output, or a UDN2983 which will not invert the output.
 
TMan1876 said:
I was planning on running them as two sets of two LEDs in series connected in parallel, if that makes any sense.

So there would be a current limiting resistor, and then it would split into two sets of two LED's in series.
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You'll want to have a current-limiting resistor for each set of two LEDs. Because of manufacturing tolerances, the voltage on the LEDs will vary slightly, and you'll end up with unevenly-lit LEDs. If you use a separate resistor for each string, they'll light up exaxctly the same.
 
I could do that, i was just trying to avoid a little soldering, but I'll probably order my led's from best hong kong, and get the resistors free.

Does anyone know where I can get a simulink model of a darlington array for me to use in my simulation. If not I can just use sets of darltington transistors instead.
 
Bump

Can anyone tell me if I will need a resistor between the 4017 outputs and the 2803 inputs?

And one last question, assuming the vcc that I send to all the components is 9V, can I just select the current limiting resistors as if there were a 9v voltage source coming out of the darlington array? Or do I need to treat it differently?
 
TMan1876 said:
Bump

Can anyone tell me if I will need a resistor between the 4017 outputs and the 2803 inputs?

And one last question, assuming the vcc that I send to all the components is 9V, can I just select the current limiting resistors as if there were a 9v voltage source coming out of the darlington array? Or do I need to treat it differently?
Click to expand...

You do not need resistors between the 4017 and 2803.

The darlington transistor in the 2803 drops 0.6 volts. So calculate LED resistors as though your voltage source is 8.4 volts.
 
You said a 2803 would invert the input, but a 2983 would not, what does this mean exactly, how would using either one of these change my setup?

Once the signal goes from the 4017 to the 2803/2983, what will the rest of the setup look like? I was imagining taking the output of the 2803 and going directly to the led arrays. Woudl this work?
 
TMan1876 said:
You said a 2803 would invert the input, but a 2983 would not, what does this mean exactly, how would using either one of these change my setup?
Click to expand...

No difference except in how you wire the LEDs. 2803 is more readily available so I would go with those.

TMan1876 said:
Once the signal goes from the 4017 to the 2803/2983, what will the rest of the setup look like? I was imagining taking the output of the 2803 and going directly to the led arrays. Woudl this work?
Click to expand...

Yes, connect the cathode end of the LEDs to 2803. And the anode end through current limit resistors to the positive voltage.
 
ok, so its going to go:

2803---(-led+)---(-led+)---(resistor)---(+voltage source-)

so the 2803 will basically act like a switch to complete the circuit for each group of led's? The groups of led's are going to be pretty spread out, so I can just connect them all to a common positive wire/node?

Thanks for all of the help, I'll post pics when the project is done around new years ;)
 
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