34 replies to this topic

[Sug]

Waaay off topic. Any help is appreciated even if it's just telling me it won't work.

I've wired LED's before, like one or 2, really basic stuff. I'm working on a project where I need 8 LED's (4 red, 4 blue) to be operated by the same switch. If possible.

I'd like to be able to have 3 selections, either the red, or the blue, or both at the same time. There will be a main switch that turns the whole setup on or off.

Also it has to run on batteries, which have to fit within the project. 4 double A's are probably the most I can fit with a single power source though I might be able to shove a couple more somewhere. Getting a couple hours of light out of it would be nice.

Going through my tackle box of parts I found a sliding switch that looks like it will do what I want. After playing around with it and 2 LEDs I believe I have it doing what I want.




Having the switch in position 1 lights LED 1, sliding it down to position 2 lights LED 2, position 3 lights up 1 & 2.

So Question 1: Is this working because it's wired correctly or am I shorting something out somewhere?

Question 2: How can I incorporate my 2 sets of different voltage LEDs into this circuit?

The red LEDs are 2.0 - 2.2 volts and the blue LEDs are 3.2 - 3.4 volts. All 20mA. I know I need resistors in there somewhere but as I haven't chosen a power supply I am ignoring them for now.

I can't really wire them in series because I would need like 15 AA's which won't fit. I've read that LEDs in parallel is a semi bad idea.

Would wiring each set of 4 LEDs in serial (4 reds, 4 blues), and then wiring those sets in parallel be a feasible solution? Could I still incorporated the 3 position switch?

Or is the voltage difference too much? Am I asking too much of 4 AAs? I'm open to other power suggestions.

Any thoughts would be greatly appreciated. : /

[Magnificent Bastard]

I'll start this off by saying I know nothing about wiring LEDs. But have you tried searching youtube for a tutorial video? Click that link and see if you can find something that will help you. We have some knowledgeable folks on this forum but youtube would be the first place I'd check for info like that.... Google is great but for tutorials you can't beat watching a video. Some information is better watched than read.

Edit: Now that I look into this a bit deeper I'm not sure there is an appropriate video. Well... I've done what little I can. Sorry this wasn't helpful.

Edited by Magnificent Bastard, 21 May 2012 - 10:00 PM.

[Sug]

Hmmm... I guess I could try some more specific searches on youtube. Part of the problem is I'm not familiar with the terminology so I'm not sure what to even search for : /

[Wyzak]

I don't know a lot about LEDs, but I do know the reason you need resistors is so the LEDs don't go overvoltage. As long as each LED in parallel has it's own resistor, I don't see why it would be bad to wire them in parallel, but the current would get split across each wire so it might be dimmer.

[SpeshlED]

I have been messing with connecting leds lately with an arduino board and they have alot of very helpful tutorials and schematics for doing that sort of thing. Try googling for something like "Arduino LED schmatic" and see what that gives you.

Edited by SpeshlED, 22 May 2012 - 07:27 AM.

[Grokmoo]

(1) You should consider reading this page, which will explain a lot of what you are asking:

http://en.wikipedia....rallel_circuits

(2) As you probably know, AA batteries have a voltage of about 1.5 V. Connecting batteries in series will add the voltages, while connecting in parallel will keep the voltage the same while halving the current from each battery. With 6 AA batteries you should not have any trouble powering 8x 20 mA LEDs. An alkaline AA battery will have a capacity of around
2000 milliamp-hours. This means that a single AA battery should have enough charge to power your 160 mA total load (at 1.5 Volts) for about 10 hours. Likewise, you could run 3 AA batteries at 4.5 V on the same load for about 10 hours.

So lets say you configure 3 AA batteries in series so that your source is 4.5 V.

You will want to connect your 2.0 volt LEDs on one line in parallel with the 3.2 volt LEDs on another line. Based on the resistance of the LEDs, you will need to put in a resistor on each track to step down the voltage over the LEDs to the appropriate voltage. The link above should really help you with that. Basically, for each parallel branch, you will want to run the line to one resistor, and then to the 4 LEDs, with the LEDs in parallel so they are at the same voltage.

I hope this is helpful.

Edited by Grokmoo, 22 May 2012 - 07:34 AM.

[VvFreezervV]

^ As mentioned, Arduino is kind of the Ubuntu of EE. There should be some easy-to-follow guides that will help you out.

A couple of points, though...

- Chemical batteries have internal resistance
You shouldn't over-current your LEDs running them off a battery. IANAEE / pull out a multimeter, but it should be safe. Coincidentally, this is why a AA battery won't "shock" you if you're clumsy enough to short it (well, that and the low voltage). 9V batteries, on the other hand, will (and make great fuse starters, shorted with some steel wool).

- LEDs (despite not having resistance) do show Vdrop (the voltage will be lower after it passes through one)
So remember to take this into account if you wire things in series. Kirchhoff's Laws, as always, will tell you what's going on.

- Know what switch you're using
It makes it possible for people on the internet to give you advice.

- LEDs in parallel shouldn't be a problem
As above, I can't think of a reason not to do it that way. It's certainly simpler for you to wire, and it's simpler to calculate from a voltage standpoint.

- When in doubt, Wikipedia
Presumably, one of the reasons you're doing this is to learn, not just make it work.

Edited by VvFreezervV, 22 May 2012 - 07:55 AM.

[SNOWHOUND]

Before you do this:

1. Do you have any knowledge of basic logic gates i.e. AND / OR / NOT?

2. To have the required lighting sequence it would look smarter to use logic and driver chips.

3. The above is not neccessary and i have devised something for you though it took me 5 seconds and requires 2 switches.

4. I have studied electronics before at a relatively high acedemic level and thats a really cr*appy circuit diagram and it may help others give you a better answer if you drew it up properly and i cannot for the life of me completely understand your diagram.

5. The flat end of the LED is negative.

6. LEDs will only need a curernt limiting resistor of ~1 - 1.5KOhm

7. Wiring in prallel requires greater current as prallel arrangement causes current to be divided amognst the given tracks.


Above is what i have come up with.
You need a 2 way switch with one other toggle switch going accross the two leds.
This gives one or the other. dependant on which way the switch is set.
and both when the toggle switch is pressed

NOTE i didnt include resistors or the battery before the first switch for the sake of simplification

Edited by SNOWHOUND, 22 May 2012 - 08:10 AM.

[veretax]

Sounds two me like what you really need is Two Switches. Perhaps a Multiplexor (man it's been a while since I've done digital logic) But essentially you can design a circuit with a truth table like this.


Switch1 Off
Switch2 Off

All Red Off
All Blue Off

Switch1 On
Switch2 Off
All Red On
All Blue Off


Switch1 Off
Switch2 On
All Red Off
All Blue On

Switch1 On
Switch2 On
All Red On
All Blue On


That's one way to handle the switching. As for the driving of the power, I'd use a voltage divider and yes some resistors to keep from blowing out the LEDs (I believe if I recall correctly that there's a direction you want power to go into the LED)


I'd have to pull out my old digital logic books to remember if there is more to it.

As for the type of switch. It might be easier to give you an idea if we saw a picture of what you were planning.

[Kiyoshi Amaya]

Just in case you're interested, here's a project I've been slowly working on using LEDs. I used a mix of 8mm, 5mm and 3mm white and red super bright LEDs (normal LEDs for the gun well and cockpit), all 3 volt on 4 separate circuits and using 6 switches. Oh and because all the LEDs I used are rated for 3.4 volt max, I just used 2 x AA batteries for each circuit and didn't use resistors.

[SNOWHOUND]

veretax, on 22 May 2012 - 08:11 AM, said:

That's one way to handle the switching. As for the driving of the power, I'd use a voltage divider and yes some resistors to keep from blowing out the LEDs (I believe if I recall correctly that there's a direction you want power to go into the LED)

Flat edge on the base of the led is -ve

[Alex MSQ]

You need a powering scheme of diods to be sure in currents and voltages - voltage divider by resistors. And also you maybe need capacitor filter.

For all of this you also need tech info about diods, their currents, opened and closed voltage.

Also to manage 8-10-20 diods you need something like multiplexor chip and about managing scheme + triggers.

And for simulation you can use old free versions of something like Microcap. I dont like to calculate capacitors, so i usually estimate capacity and test it in simulation.

Edited by Alex MSQ, 22 May 2012 - 09:17 AM.

[Sug]

Lots of helpful info and lots to read. Thanks all

Wyzak, on 22 May 2012 - 07:21 AM, said:

As long as each LED in parallel has it's own resistor

Grokmoo, on 22 May 2012 - 07:33 AM, said:

Basically, for each parallel branch, you will want to run the line to one resistor, and then to the 4 LEDs, with the LEDs in parallel so they are at the same voltage.

Is it better for LEDs in serial to each have their own resistor or is one resistor in front of all the LEDs sufficient?

VvFreezervV, on 22 May 2012 - 07:53 AM, said:

^ As mentioned, Arduino is kind of the Ubuntu of EE. There should be some easy-to-follow guides that will help you out.
Presumably, one of the reasons you're doing this is to learn, not just make it work.

Is is bad that I gave up on Ubuntu after about 5 minutes? Learning seems to be the side effect of these projects. Unfortunately it just makes me want to do things that are even more complicated.


Snowhound and veretax, I actually had to duck as your posts whooshed over my head.

veretax, on 22 May 2012 - 08:11 AM, said:

As for the type of switch. It might be easier to give you an idea if we saw a picture of what you were planning.

This is the switch I currently have. My plan to wire the LEDs is something like this:



I think this setup, with appropriate resistors, will let me run the 2 different sets of LEDs off the same power source.

My first post shows the way my switch is set up now. With 2 single LEDs this works the way I want it to. I'm wondering if I can just drop in the above LEDs sets in place of the single LEDs. Something like this:

Shrekken, on 22 May 2012 - 08:50 AM, said:

Just in case you're interested, here's a project I've been slowly working on using LEDs. I used a mix of 8mm, 5mm and 3mm white and red super bright LEDs (normal LEDs for the gun well and cockpit), all 3 volt on 4 separate circuits and using 6 switches. Oh and because all the LEDs I used are rated for 3.4 volt max, I just used 2 x AA batteries for each circuit and didn't use resistors.

I'm still in the planning stage of my project as i have about 3 months to complete it. I'm making one of the rifles from Mass Effect for a friend, for a convention. I've made stuff like this before but never added any lighting, mainly because we're usually working at the last minute.

So since I have plenty of time for this build I'm trying to incorporate as much detail/complexity as I can, and then cut things out if I can't handle it or run out of time.

So basically I'd like this prop to have the different color lights on a sliding selector switch to represent the different ammo types. The LEDs will be pointed at a piece of acrylic running along the inside of the barrel shroud. At each slot in the shroud I'll etch the acrylic so it catches the light.

I've set this up on a test piece using single LEDs and the effect is great. Since I could wire 1 set of LEDs (red) fairly easily I decided I am to add another set of a different color (blue), and since I had 2 colors of LEDs I figured why not have both sets on at the same time to make a purple/magenta color.

This is where I ran into trouble with the different voltages and the switch wiring : /

Again, thanks for all the replies. Lots to think about and lots to read

[SNOWHOUND]

Sorry if it was a bit much.
It is best to explain it in those terms for consiceness and accuracy.

If you read up on circuit diagrams (only takes about 5 mins) and create one in terms of this circuit.

It will help you see things more clearly.

- Dont place LEDs in series as voltage drops accross each one i.e. if you have a 9V battery with 8LEDs and each LED takes 1.5V the 9V is spread accross each LED.

A few LEDs in that config. dont work too well that way from my experience.

[Lasgo Treem]

I agree with Snowhound that you don't want your four LEDs in series. You want to put them in parallel.

I don't quite understand how that switch works. However the only way I believe you can do what you want with that single three position switch is with a couple diodes. You will run a line from one switch position to turn on the red LEDs, another line from the second switch position for the blue LEDs, and the third position for all LEDs.

The logic gating problem is that ultimately, there will be electrical connectivity to ALL the LEDs. So any swtich position will actually turn all the LEDs on. You can solve this by placing a normal rectifier diode in the lines from the third swtich position to the red and blue LEDs. The diode only conducts in one direction. So the third swtich position will turn on all LEDs but block that outcome with the other two.

Without the diodes you'll need two swtiches (I think). I don't know if that made sense at all. If there was an online schematic program free to use, I could make you a schematic. I'm not aware of one though.

[Kiyoshi Amaya]

Awesome project! Just as a thought, you could use a 3v lithium button cell for the power, something like a CR2023 cell (the same type found on PC motherboards). That wouldn't take up much space at all.

[Sug]

I'll add circuit diagrams to my homework : /

Shrekken, on 22 May 2012 - 02:13 PM, said:

Awesome project! Just as a thought, you could use a 3v lithium button cell for the power, something like a CR2023 cell (the same type found on PC motherboards). That wouldn't take up much space at all.

Those little button cells are in the back of my mind as a possibility. Though the cost is kind of a deterrent and they wouldn't last as long as AA's.

[Alex MSQ]

Use this way

[Alex MSQ]

Resistors in parallel getting R1=R^2/2R so you get another current and another voltage at diods.
Use 1 resistor. And if you dont use MOSFET key, use capacitor filter.

[Alex MSQ]

And get in mind - current at resistor is a sum of currents in diods.
You have to give minimal opened current to every diod but not bigger than maximum current. And you need to give opening voltage to every diod by resistor. The bigger current in diods, the bigger voltage gets resistor and lower voltage get diods.

You can use resistor at every group of diods, but paralleling resistors may get you diods not open or diode breakdown.