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
Best Answer
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.