Flashing LED project

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johnk

New Member
I'm a newbie, but I'd like to make something with flashing leds. Ideally, I'd like the leds to change their state at the same time but to remain off or on independently. Can someone tell me what parts I need and a good intro in how to wire up the project?

Also a good cheap source for parts, of course!

Thanks

John

John Sorensen

New Member
You can use a 556 timer IC to set up two flashing rates. If you want to have LEDs change state at the same time, hook one up to be on when it is "sunk" and the other to be on when it is "sourced." Research 555 astable circuits, and sinking and sourcing LEDs (a 556 is just two 555s in one IC). 555 circuit examples are cheap and plentiful on the web.

If you live in the US, get your parts from Digikey-- they're outstanding.

If you go to Radio Shack I'll pinch my nose in disgust and never help you again

HTH, have fun,

j.

johnk

New Member
Thanks

I want to make a bunch of these. Do I just get a plastic circuit board that is all pre-holed, then just solder the parts in?

When i say I'm a newbie, I mean I started this week!

John

John Sorensen

New Member
Well, the absolute first thing you need is a breadboard. If you just start soldering things, you'll get very frustrated very fast. A breadboard lets you just plug things in, try them out, and toss out the smoldering parts easily. You can get breadboards (presumably at Digikey), but also at (ugh) Radio Shack, AllElectronics.com, etc.

If you decide to go the 556 route (or just buy a couple 555's for flexibility) then research the circuits and buy the parts to go with that. If you're serious about getting into this, buy a handful of parts:

Resistors: 10ohm, 100ohm, 1kohm, 10kohm, 100kohm, 1Mohm
Capacitors: 1nF, 10nF, 100nF, 1uF, 10uF, 100uF
Inductors: don't get any now
Buy some transistors: 4400 (NPN) and 4402 (PNP) or 3904 and 3906
Diodes: 1N4005 or whatever. If you're desperate enough, you could use the base-emitter junctions of the transistors (groan)
Some LEDs: Whatever trips your trigger.

Buy like a dozen of each-- they're not expensive. Whatever you do, buy at least three of each. This is true, at least as far as I'm concerned, with whatever you buy. The reason is, when you have a problem, you can do a best-out-of-three comparison to tell if it is the component or the circuit that is the problem.

Remember the old saying, "Never go to sea with two chronometers [clocks]. Either take one or three."

Once you get a circuit working, then buy some boards to solder stuff into. Different people have different techniques for doing this, so do some research into that. I prefer boards with 3 or 4 holes-per-pad. Radio Shack (ugh) has some ok small boards for this, but for bigger ones go to Digikey, AllElectronics, etc.

j.

John Sorensen

New Member
BTW, larger "Protoboards" can cost between $10 and$20 apiece. Therefore, if you're making more than one of something, and if you're time is worth anything (read: you have more money than time) then it can be cheaper to have the boards made for you. For that I prefer expresspcb.com.

j.

johnk

New Member
OK, so the pre-holed board is called breadboard. I'm learning, I'm learning.

Theres a prebuilt one that might be adequate for \$15 before postage. Is building one cheaper?

I'd also like to put this in a cheapo case, like a cardboard box with holes for the leds. With a double a battery, or whatever will run it, it wouldn't require special insulation, will it?

John

johnk

New Member
Kewl. Thanks.

Is there a good place to get dummie instructions on this project? I can find schematics, just need plain language instructions.

Any help appreciated.

Thanks

John

mattg2k4

New Member
this is a great tutorial on using the 555 timer. It's about as dummy as they come. Just figure out the timing you'd like, and run the equations they give you until you find values that work for you. Try not to get either of the resistors too low, say 1k minimum. This is a rule of thumb I heard, I guess it might be less accurate below that.

Simply hook up a led to pin 3 of the 555. The values of the two resistors and capacitor will determine how fast they flash and how long they are on and off. If you're using a lot of leds at once, that may have a greater current draw than your chip is built for, then hook a transistor up to pin 3 and run the leds off of that.

Since you're new, I'll also refer you to this set of free downloadable books. I highly recomend that you read them.

Gene

New Member
Please keep in mind that you can do different things with LEDs and a 555 is only one route. Maybe it would be useful for you to decide exactly what you want your LEDs to do, how many LEDs you want to have in your project, what the power source will be, etc. It will be easier to decide on a circuit after you have decided on the project itself.

For instance, you can make a flashing LED with one battery, one LED, and one resistor. As a learner, this might be a good place to begin. Oh, and as to it possibly being cheaper to buy a circuit ready-to-go . . . if you do it yourself, you will learn something new, leave with a true sense of accomplishment, and, yes, it will probably cost less.

johnk

New Member
My project

I want 8 leds to be changing states maybe three times a second, and I want the change to happen for all 8 at the same time. I would like the power supply to be battery power, hopefully no more than two double AAs.

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