100 LED chaser

Thread Starter

Ron H

Joined Apr 14, 2005
7,014
Has anyone ever posted, or seen online, an LED chaser (one direction, one LED at a time) that will handle up to 100 LEDs while requiring only two CD4017s, plus 20 transistors and a handful of resistors? The length can actually be arbitrary.
As with all chasers, it also needs a clock oscillator, and maybe a power-on reset, both of which are made here with a Schmitt trigger quad NAND package.

I'll post the basic 100 LED version here. The arbitrary length version requires a few more parts.

If this is a common approach, I hope you'll forgive my ignorance. I am not an LED chaser guy, normally.
 

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Wendy

Joined Mar 24, 2008
22,582
Ummm, I'm stealing this. OK? I'll probably add it to my light chaser article.

You can set an arbitrary count with a very simple diode AND gate. Easy peasy.

If you are going to use driver transistors I would also add sinking transistors to get the full benefit of current amplification.

I really love this, it is neat.
 
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Thread Starter

Ron H

Joined Apr 14, 2005
7,014
Ummm, I'm stealing this. OK? I'll probably add it to my light chaser article.
Sure. Credit would be nice.:)

You can set an arbitrary count with a very simple diode AND gate. Easy peasy.
That was my plan, although if you want to retain the power on reset, you also need to OR the original one with the output of the AND gate.

If you are going to use driver transistors I would also add sinking transistors to get the full benefit of current amplification.

I really love this, it is neat.
Sinking transistors drive the rows. Sourcing transistors drive the columns. Am I missing your point?

BTW, for the benefit of NOOBs: The LEDs can be arranged in any geometric fashion, such as a line, a circle, etc.
If you need a shorter chaser, unused transistors and resistors can be eliminated.
 

Wendy

Joined Mar 24, 2008
22,582
Full name or just forum link? I understand wanting credit, just tell me how you want to be listed. If you don't want to do it here send me a PM. That way only folks who only read the article will know (whatever there is to know).

In your drawing you have the Vcc 4017 providing all the current, I suspect this will still limit it to 6.8ma, though I would have to check the data sheet to be sure. A simple emitter follower for each output will solve this problem.
 

Thread Starter

Ron H

Joined Apr 14, 2005
7,014
Full name or just forum link? I understand wanting credit, just tell me how you want to be listed. If you don't want to do it here send me a PM. That way only folks who only read the article will know (whatever there is to know).

In your drawing you have the Vcc 4017 providing all the current, I suspect this will still limit it to 6.8ma, though I would have to check the data sheet to be sure. A simple emitter follower for each output will solve this problem.
Are you looking at the same drawing that I am? Both 4017s have transistor buffers. The LEDs run at ≈20mA.
 

Wendy

Joined Mar 24, 2008
22,582
My bad, I did miss the other set of transistors. So stealing it as is it is then (but you will get the credit).

If you don't mind I am hijacking this thread, rather than starting a new one, to explore this circuit further. Long term I may even come up with a PCB for the basic designs and post them here, and then there is adapting it to sweep back and forth.

This one will keep me busy for a while.
 

Thread Starter

Ron H

Joined Apr 14, 2005
7,014
My bad, I did miss the other set of transistors. So stealing it as is it is then (but you will get the credit).

If you don't mind I am hijacking this thread, rather than starting a new one, to explore this circuit further. Long term I may even come up with a PCB for the basic designs and post them here, and then there is adapting it to sweep back and forth.
That's gonna be tough, unless you can find (or make) an up/down Johnson counter/decoder.

This one will keep me busy for a while.
I would love to see a PCB. I was thinking a circle would be cool. I think it would require a double-sided board, or a lot of jumpers.
 

Markd77

Joined Sep 7, 2009
2,806
And that impedance is defined how? By the 4017?

Do yourself a favour if you are going to build this circuit, use a PNP.

Or you drop voltage with the transistor.
It's the 300 ohm resistor R11 at the very bottom that limits the base current in the transistors Q11-Q20. No reason to use PNPs.
 

Thread Starter

Ron H

Joined Apr 14, 2005
7,014
And that impedance is defined how? By the 4017?

Do yourself a favour if you are going to build this circuit, use a PNP.

Or you drop voltage with the transistor.
We have LEDs that have a fwd voltage of 2 or 3 volts. We have a 9V supply. Somewhere, we have to drop an extra 6 or 7 volts. I chose to drop 0.7V across an emitter follower. The remaining drop is across R11. This is more efficient than a PNP. With a PNP we would have to have a base current limiting resistor (more parts), and supply enough current to guarantee saturation (more currrent). The NPN emitter follower base current is automatically limited by beta. Furthermore, PNPs would require 10 inverters, since the pulses are the wrong polarity.
 
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vrainom

Joined Sep 8, 2011
126
I have designed a lot of commercial high-tech stuff. Despite all that, I like low-tech. So do a lot of other people here.
Amen to that. There are a lot of ways to do things and it's fun to think about the different ways to get to a solution.
 

Wendy

Joined Mar 24, 2008
22,582
I will probably make a uber simple LED grid just to demonstrate this. It also solves another problem I've been mulling for several years, I want to make a digital LED clock that looks analog, 60 seconds, 60 minutes, that kind of stuff. The parts count is satisfyingly low with this.

I'm thinking of a simple 20 pin ribbon connector to connect two boards together. It would make modifications pretty easy.

I think you mean common collector.:)
So it is. I'm thinking of steering diodes for a sweep, though I'm not sure the idea will work. Gives me something to think about walking and driving.
 
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GopherT

Joined Nov 23, 2012
8,012
You could use a multiplexer and counter instead of a 4017.

74HC4067 multiplexer allows 16 outputs so two could control a 16x16 array.

The multiplexers need a counter. Interestingly, one 8 bit up/down counter (DM74LS469 for example), could drive both multiplexers. the lower four bits to drive one multiplexer and the upper 4 bits could drive the other. That way, you could travel across x-axis 16 steps (bits 0-3), then index on the y-axis when the higher 4 bits increment. This device allows up/down counting by toggling the U/D bit.

Alternatively, separate 4-bit counters could be used to drive x and y position separately (or use bdc counters if you want to limit to a 10x10 matrix and still use the above-listed multiplexers).
 
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