Help with wiring some LEDs for a cosplay.

[dethkruzer]

Hola Peeps. I'm not gonna lie, I'm a complete scrub when it comes to this kind of stuff, which is why i'm here, hoping to get some advice.

I'm planning on doing a cosplay for which I would need some LED lights. Specifically, I need two LEDs that flash in an alternating pattern, preferably with a pushbutton to activate it.

Now I've done some googling, and I came across the Make Magazine project (http://makezine.com/projects/555-timer-blinky/), which pretty much seems to fit the bill, minus the pushbutton. I also did some research into switches and pushbuttons, and was wondering, if I wanted a simple normally open, single-pole single-throw in the design shown in the link above, should it be placed on the red or black wire coming from the power supply? Or is this irrelevant?

Also, Since i'm here writing this, I might as well ask about tthe 555 timer chip used in the Project. Could someone explain to me, preferably in laymans terms, what affects the rate at which the LEDs would blink? Is there some way to calculate the frequency of the blinking?

Thanks.

[DavidSh]

It shouldn't matter whether you put the switch in the red or the black wires.

And there is a Wikipedia page on the 555 timer IC chip, which tells me (in the section on the "Astable mode") that the timing is controlled by the capacitor and two of the resistors, the ones that are listed as 1 mega Ohm. The formula is something like
Time 1 = ln(2) * C * ( R1 + R2)
Time 2 = ln(2) * C * R2
where R1 and R2 are the resistances of these two resistors, in Ohms, and C is the capacitance of the capacitor, in Farads.

The basic intuition is the circuit operates in one mode, pushing current in one direction, while the capacitor charges. When the capacitor reaches a certain charge, the circuit is switched over to another mode, pushing the current in the other direction, and the capacitor discharges. The times for the capacitor to charge and to discharge depend on the capacitance, and on the resistances.

[Kato]

Yeah, not too much to add to the earlier description... better not try to understand that circuit diagramm, it will only give you a headache. I think the basic idea is it manages the output being constant, not the curve the capacitor puts out, but even then it seems too complicated, you could just use a transistor... but I'm not into electronics, I'm sure they know what they are doing.

Er, yeah, as was said, the overall time of a cycle is given by T=ln(2)*C*(R1+2*R2), with the longer part being ln(2)*C*(R1+R2) and the shorter ln(2)*C*R2, which with the recommended resistors give you something like 1 second intervalls. Use larger resistors or capacitors for longer intervalls.

If you've never done it, be careful about the soldering. At least I, lacking much experience, fried a transistor recently which is kind of a pain. But the parts shouldn't be too expensive so maybe buy a few spares to begin with.

[dethkruzer]

Thanks. I've done some soldering maybe... 7 years ago, but I'll try to be careful.

Just wanted to clear up a few things. Are the 1 megaohm resistors in the above link just related to the cycle duration, or do they somehow also relate to something like not burning out the LEDS? It would seem to me that that's waht the 100 Ohm resistors ar for, but I thought I might as well ask. Would I risk damaging something if I were to say, halve the resistance of those 1 megaohm resistors, meaning roughly two cycles per seconds? Or should I rather just decrease the size of the capacitor if I wanted to cut the time of the pulses?

[Gray Mage]

It doesn't matter which wire you put the button, it'll work the same. If it's your first time soldering, I highly recomend buying an IC socket for the 555, as soldering it directly without any experience is a good way of burning it.

The circuit works with the voltage in the capacitor trigerring comparators inside the IC, thus giving an on/off output. The resistors change the rate in which the capacitor charge, and thus the time of the blinking LEDs.

Edit: The 1Mohm resistors should be the ones to detrmine the time. The 100ohm ones are in series with the LEDs so they are the ones responsible for the LED not burning up due to excessive current (not sure it'd happen considering the max output of the 555 but it's always best to be safe). Tampering with the 1Mohm or with the capacitor shouldn't change more than the time. Just be carefull if using an eletrolytical capacitor, as these have a given polarity you must be consious of.

[wumpus]

Some thoughts from a sometime EE.

The socket will cost more than the 555. It is still worth it as you can heat it up as much as you want without wondering if the chip still works.

LEDs are current devices. The brightness depends on the current (and for real efficiency you light them at the recommended brightness and dim them by flashing on and off (a few thousand times a second. 555s are good for that). You probably don't need to worry about how you dim them, just make sure there is a resistor between the voltage source and the LED. The LED will drop the voltage by about 1.3Volts, so subtract 1.3 from the voltage source and that is going through the resistor. The current is the voltage (source - 1.3) divided by the resistance of the resistor (choose the resistor depending on what the LED manufacturer recommends: there should be a datasheet for it and somewhere a recommended current. If this is too bright, you can use a higher resistance).

The LEDs are also heat sensitive. You might want to clip something to it (any metal clip should work. I've used aligator clips, but the type of thing to hold [potato/tortilla] chip bags closed will do in a pinch, as long as they are metal). The resistors aren't heat sensitive, so solder them first if you've never soldered before.

I'm guessing the above 555 info is right. Haven't used one for decades, but they are a classic chip.

[Fri]

I majored in product design in college, and sometimes we had to make the prototype of our designs. Sometimes those tats need circuits. And I'm pretty much really bad at circuit building. I don't know if it's available in your place, but back then when I need some wiring or circuiting done I can ask some person in the electronic shop for some money. Better than waste the chips and such.

Man, I miss that place. Back then, where I used to buy stuffs for my projects is some sort of electronic-part mall. It's a collection of stores that sell various kind of electronics and weird electronic parts, ranging from common gadgets and PC parts like radio, ram or hard drive or graphic card, to specialized building needs like various soldering tools, IC chips and cannibalized old electronics. As you can imagine, it doesn't really look as tidy or as clean as normal mall. In fact, I always thought it looks like a bazaar from some post apocalyptic, steampunk/cyberpunk, or fantasy setting. Or at least a setting for a fight from a hong-kong gangster movie gunfight.

[dethkruzer]

The LEDs are also heat sensitive. You might want to clip something to it (any metal clip should work. I've used aligator clips, but the type of thing to hold [potato/tortilla] chip bags closed will do in a pinch, as long as they are metal). The resistors aren't heat sensitive, so solder them first if you've never soldered before.

So, is that metal thing clipped on to basically soak up the excess heat conducting up the leads?