Alternating Output LED Driver

[Mishael]

I'm modifying a chainsaw for halloween (which is very close, i know) and, instead of having the chain, I want to wire up a bunch of LEDs that alternate. Basically all i need is a circuit that alternates the output between two seperate drivers at a constant speed. And id like that speed to be relatively fast, or even adjustable. It would need to power upwards of 100 or so 20 mA, 3 VDC max LEDs so if i need to beef up the circuit, then so be it. If i had time and/or knowledge of what i was doing, i could very easily just research this myself but i was hoping here i can get explanations, kit options, and some choices in what im doing. Thanks!

 

[electro_phunk]

Do you know anything or have heard of a LM555 IC? Do you have access to electronic components?

 

[Mishael]

i believe that is the 555 timer. in which case, yes i am familiar with it. i havent done much work with it, but i have used them in circuit kits. as for access to components, whatever radio shack has is what i have access to

 

[electro_phunk]

I would recommend using a 555 timer IC and a decade counter. If you follow this link: **broken link removed** , then you can select which one is best suited for your project. You may run several of those simultaniously to create a nice chain saw effect. Hope this helps.

 

[Reloadron]

I would go with the suggestion of electro_phunk and what you actually want is called a LED Chaser Circuit. You clock a 4017 counter chip which gives you 10 outputs sequentially. Similar to what you see here. You can use a 555 for the clock or any number of basic clock circuits. You would take the 4017 outputs and drive transistors and let them drive the LEDs. This way you can get several LEDs per leg of the 4017. 0 through 9 maybe 4 times (40 LEDs). A Google of LED Chaser Circuits will bring up plenty of variations. I just don't think Radio Shack still carries the 4017 counter chip? They do have the 555 and boards to build on.

Ron

 

[Mishael]

I like what im seeing but is there any cost-effective way of having more LEDs aside from what i can figure out which is just using relays? (i dont think they are a very viable option). The chainsaw has a 14 inch bar so i figure at least two LEDs/Inch, so thats somewhere in the low 30s at least, but i was hoping for at least 3 LEDs/inch. I have seen a circuit kit that alternates at variable speeds through only two channels but i dont think the circuit has enough heft to carry 20+ LEDs/channel, especially the LEDs that i was hoping to use, because they have a high forward voltage and current. I know i could use microcandella LEDs but i have an obnoxious amount of bright red ones that i need to use for something. the issue with the 10 channel output is that i would have to wire up everything in a very specific way, and it is not conducive to time constraints. Having a tree circuit is my easiest option with two different outputs, instead of ten

 

[Reloadron]

Relays? There are no relays. You are missing something here. See the attached images.

The first image is a very basic clock using a 555 to drive a 4017 counter chip. The second image is the effect from the circuit. Now that is only 10 LEDs, however, rather than connect the LEDs directly to the 4017 as shown each output of the 4017 drives a 2N2222 tiny cheap transistor using about a 1 K Ohm base resistor. You simply place 3 LEDs on each leg using this method. That will give you 30 chasing LEDs. You can buy a small board at Radio Shack for a few bucks that will hold everything. The 555 and other timer parts can be bought at Radio Shack for a few bucks, the LEDs and 1 K resistors and transistors can be bought at Radio Shack. Everything but the 4017 and they may have that too.

Ron

 

[Mishael]

unfortunately, radio shack does not have the 4017. now with high draw LEDs (what im planning on using), do i risk overloading the 4017? Id also like more than 30. Is there any way i can get any more easily?

 

[Reloadron]

OK, let's take a look at the whole picture here and gain a little understanding of the circuits in general using the CD4017 Decade Counter/Divider. For each incoming clock pulse of low to high the 4017 outputs will sequentially go high, Q0 through Q9 for a total of 10 outputs. One and only one output is on at a given time. The 4017 outputs can drive an LED but only a standard generic low current LED. That is why when you see chaser circuits using the 4017 there are only single LEDs on each output.

When we want to drive more than one LED we need to use a transistor to handle the added current. Now the 4017 drives the transistor which drives the LEDs. The LEDs are placed in parallel at the transistor collector and each LED has a series resistor. I mentioned using 2N2222 transistors which will easily handle a current of 500 mA which is a heck of a lot of 20 mA LEDs or even 5 100 mA LEDs.

I made a brief cartoon of what I am getting at. See the attached image. I used 3 LEDs for each leg but you would just add more in parallel. Long as you don't exceed the transistor ratings.

Ron