100 LED chaser with multiple LEDs on at the same time

Question

I'm sure this has been covered but I am not finding answers to what I am looking for. Just getting back into electronics after well over a decade...so I'm a bit rusty. :)

What I need is a 100 LED sequence broken down into 20, 5 LED segments, with LEDs lit in pairs as they chase. Ideally 1/2 on, 3/4/5 off...1 off, 2/3 on, 4/5 off...1/2 off, 3/4 on, 5 off...1/2/3 off, 4/5 on. Something like that (visually represented below). Always 2 LEDs lit and 3 unlit for each 5 LED segment. I've broken out my old lab kit (was shocked at the amount of dust on it) and to my surprise I found my packet of first gen blue LEDs. I remember having to special order them and they cost me $10 each. That'll tell you how long it's been. But I have all manner of parts and was hoping that using a 555 and 4017 (I have a tonne of these) as well as some combination of transistors or inverters is what I'm looking at here. Chances are I have the parts on hand already. But I'm straining my brain trying to figure out a workable and SIMPLE circuit that can drive that many LEDs in the pattern I'm seeking. Bonus if I can regulate the speed of the chase.

Any advice, input or thoughts is GREATLY appreciated.

OOxxxOOxxxOOxxx

xOOxxxOOxxxOOxx

xxOOxxxOOxxxOOx

xxxOOxxxOOxxxOO

x=OFF O=ON

Answer 1

4017 output is 'one hot', and won't source much over 1mA, so you can't use that directly.

If you must employ a 4017, then the simplest way to get to a base-5 chase sequence is to use diode logic to connect the 10 outputs to the bases of 5 NPN driver transistors. So output Q0 connects by 2 diodes to TR0 and TR1 bases. Output Q1 connects by 2 diodes to TR1 and TR2 bases, etc etc. Total bill of materials 20 diodes, 5 current limiting resistors on the bases, and five transistors. If you use a driver array like ULN2803, then you don't even need the base current limiting resistors. That array goes up to 50v, so you can put LEDs in series to reduce the current requirement.

Finally, use an oscillator to drive the clock pin. A variable speed clock varies the speed of the chase.

Answer 2

Use a 556 (or two 555) and a shift register.

Make one go at a desired rate but most crucially set its duty cycle at 40% (that's your pattern generator) and feed its output to a shift register's data input (be aware that since this duty is less than 50% you have to actually set it to its reciprocal, 60%, and then invert it).

Put the output of the other timer to the clock input of the shift register and tweak the timer frequency until it's 5 times that of the first timer or until you see the pattern/speed matches what you want.

Answer 3

This isn't a full answer if this is about using all the parts you already have on hand, but you mentioned an hour ago you are flummoxed by driving two LEDs in pairs. So I thought I'd start there since that's not so hard.

Look at the following schematic, which only uses four LEDs instead of five (for space-saving reasons only.) There are three input lines, each of which turns on two adjacent LEDs. This would be a 3-state case, of course. But that's one possibility.

^{simulate this circuit – Schematic created using CircuitLab}

You could also consider using two different counters similiar to (but not necessarily the same as) your 4017. If both were initialized to the same starting state, the following similarly short-handed case might look like:

^{simulate this circuit}

Also, only 3 states (for brevity again.) I've no idea why you might decide to go that way over the other. But you might come up with a reason, so there it is, as well.

The overall problem faced might be figuring out how to get 4 states out of a 10-state device, or to find a way to combine 10-state devices into a 20-state or 40-state situation where you could then divide that evenly back into 4 states without what amounts to blanking periods.

I'd probably sell the 4017s online in nice packages, get the money back for them, perhaps sell those all-too-expensive blue LEDs, too, and then pick up some really cheap LED modules (which can be bought with drivers included) and get a microcontroller and do it that way. More versatile for the future (and I think you'd imagine some fun ways to use that flexibility as time goes on.)