Help needed - very simple wiring diagram

[Sulla]

I know this has been asked, but I've had trouble dredging up anything in search.

I am scratch building some trek tools and need to cobble a simple push button LED rig. Push the button and hold it, the LED stays on. Let the button go, the LED shuts down. I'd like to keep the battery to a single AA or maybe a 9 volt as I have to fit this into a plastic tube about 1" in diameter (I can dremmel space for a 9v if needed.)

I'd like to just get this stuff at Radioshack or some other close-to-me place.
Red LED
Battery Holder
Small switch
resistor
(I have wire and solder)

Sorry for the crude drawing, I did it in a hurry this morning on paint.

 

[Mike Rush]

The diagram looks fine... sorry to be dim, but what help do you need? :confused

 

[Sulla]

My fault... I need help picking the hardware out. I understand the basics, but not the LED, what type of resistor (or if it's even needed) even what the switch is called so I can go pick one out.

What I need:

• Do I need a resistor?
• What kind of resistor?
• Can I use a single AA or a 9v?
• What kind of red LED do I need? (I have about 3/16" to 2/8" clearance for it)
• Mainly the battery and resistor and what kind off switch is a press and hold = on/do not press = off.

 

[feek61]

My fault... I need help picking the hardware out. I understand the basics, but not the LED, what type of resistor (or if it's even needed) even what the switch is called so I can go pick one out.

What I need:

• Do I need a resistor?
• What kind of resistor?
• Can I use a single AA or a 9v?
• What kind of red LED do I need? (I have about 3/16" to 2/8" clearance for it)
• Mainly the battery and resistor and what kind off switch is a press and hold = on/do not press = off.

Yes, you do need a resistor and it will depend on the LED that you get. LEDs are all different. Here is a helpful link that will tell you what size resistor based on the voltage and LED specs:

http://led.linear1.org/led.wiz

You can basically use which ever voltage you desire (ususally over 3 volts) but the wizard above will tell you if your voltage is adequate. You can also use small watch batteries if size is a factor and it sounds like it is. Just pick out your LED and then go from there. All of the specs of the LED will determine what size resistor you need. Also keep in mind that LEDs are polarized so there is a positive and a negative leg. The resistor will go to the negative side (the negative side on your drawing would be the top side that connects to the resisitor). I hope this helps. Don't be afraid, it's really pretty simple.

EDIT: BTW, the short leg of the LED is the negative side!! It makes a difference

Will

 

[CustomCreations]

Iedited as above sums it up!

Its a push to make switch BTW.

 

[Sulla]

Awesome, thanks all!

 

[GrenadeKing]

The switch your looking for is called a momentary push-button switch. Basicaly, its a switch that you have to hold down to make the connection.
Radioshack used to have a 4 pack of some that were pretty small. I think they're about 3/8ths wide and 3/4ths long. If your using a 1" pipe they should be plenty small enough.
As for batteries, usualy 3 volts is good enough for one LED (still need a resistor of coarse). Those 3 volts you can get from a variety of scources, such as a simple watch battery as mentioned before. They'll last fairly long too. Personaly, I'd get two 1.5 volt watch batteries and run them like a simple flashlight. I'm not sure, but I think they'll last longer that way.
As for the rest, I think everybody else covered it pretty well.

 

[feek61]

Let me know if you need any more help.


Will

 

[Sulla]

Since I am using a monetary push button switch, does it matter if I wire it in between the battery and the LED, the LED and the resistor, or the resistor and the battery?

Radioshak 5mm red LED – 1.7 typical voltage, 20mA, with a source voltage of 3.

Here is what LED series parallel array wizard gives me:

 

[GrenadeKing]

It shouldn't matter, as regardless of where you put it, it'll be cutting the flow of current and breaking the circuit, thus serving it's purpose.

If I were building it, I would run the positive from the power source to one of the switch terminals, then run the other terminal to the positive end of the LED, then the negative from the LED to the resistor and then to the battery. I don't know if it's "correct" but, that's how I'd do it.

In case you don't know how to tell what resistor is what, this page here should prove somewhat useful:
http://wiki.xtronics.com/index.php/Resistor_Codes
I'm not sure if Radioshack has individual resistors, but they should have a few bundle packs and the package should tell you which kinds are in it. You still have to use the color code to actualy find the one you need if you do end up getting one of the bundle packs though.


I was under the impression that the resistor was supposed to go on the positive end. Maybe somebody else can explain? :confused

 

[masterjedi322]

does it matter if I wire it in between the battery and the LED, the LED and the resistor, or the resistor and the battery?

As long as you keep everything in series, as you have diagramed in your initial drawing, it shouldn't matter where you put the switch. I typically put any switch right after the battery, but that's more of a personal preference and really has no technical basis.

Sean

 

[rjmarthaller]

it doesn't matter where you put the resistor as long as it's there and the correct one.

 

[Sulla]

Been shopping around. The wizard suggested I use a 1/4W 68 ohm resistor. Would a 90.9 ohm-1/4W resistor work?

What are the rules here? If I need 68 ohm can I go a little high (90 ohm) or a little low (40 ohm), or tripple up on three 20 ohm, with out burning anything out or ruining batteries or something?

 

[motman241]

Radioshak 5mm red LED – 1.7 typical voltage, 20mA, with a source voltage of 3.

That tells me the batteries need to be at 3 volts. 3 volts equals 2 cells - AA, AAA, C, D, and you'd have to look at watch batteries to make sure of voltage. Just put two of them together and you're good.

Usually, the bigger the cell, the longer they last - a flashlight with 2 Ds will work longer than a flashlight with 2 AAAs (although they run at the same voltage).

*edit - oops, forgot to add that at 3 volts, there would be no need for a resistor.

 

[feek61]

Been shopping around. The wizard suggested I use a 1/4W 68 ohm resistor. Would a 90.9 ohm-1/4W resistor work?

What are the rules here? If I need 68 ohm can I go a little high (90 ohm) or a little low (40 ohm), or tripple up on three 20 ohm, with out burning anything out or ruining batteries or something?

Yes, you can go a little higher or lower without anything bad happening, lol.


Will

 

[Sulla]

That tells me the batteries need to be at 3 volts. 3 volts equals 2 cells - AA, AAA, C, D, and you'd have to look at watch batteries to make sure of voltage. Just put two of them together and you're good.

Usually, the bigger the cell, the longer they last - a flashlight with 2 Ds will work longer than a flashlight with 2 AAAs (although they run at the same voltage).

*edit - oops, forgot to add that at 3 volts, there would be no need for a resistor.

So I could use 2 AAA's? I was thinking of using a single 3 volt Energizer 2025 lithium. But 3 AAA's would be easier for me. I already have AAA battery holders I think would work.

Out of curiosity; can a quick and dirty battery holder be made from wire and styrene? I was thinking of a 3 volt disk battery (Energizer 2025) sanwitched between two pices of styrene with the wired poking through them and coiled on the pos and neg side of the battery.

 

[feek61]

Yes, I just made one very similar. All you have to do is to have something to hold the battery and one contact on each side. Really pretty easy to do and a lot smaller then the AAA batteries. What you have drawn will work but it would be better if you go with some thin brass and made contacts instead of just a coiled wire. The wire probably is not stiff enough to maintain a tight contact to the battery. Especially if what you are doing will be moved around.

Will

 

[exoray]

I was under the impression that the resistor was supposed to go on the positive end. Maybe somebody else can explain? :confused

It makes no difference... It's more a matter of 'doing it by the books' philosophy, but in reality it has no effect...

Same thing with switch location...

 

[Sulla]

Thanks. You all have been very helpful!

 

[motman241]

So I could use 2 AAA's? I was thinking of using a single 3 volt Energizer 2025 lithium.

Yup.
AA = 1.5 volts
AAA=1.5 volts
AAAA=1.5 volts
C = 1.5 volts
D = 1.5 volts

1.5 + 1.5 = 3 volts. (as long as you connect the + of the one battery to the - of the other battery)

And those numbers are assuming that they are not rechargable batteries. (when in doubt, just look at the package)

No need to spend an arm and a leg for some weird battery (and good luck finding a holder for it), when the average run-of-the-mill batteries work just fine.