# On-Off-On switch for 2 series of LED lights (newbie)

Discussion in 'The Projects Forum' started by AFPara, Feb 5, 2015.

1. ### AFPara Thread Starter New Member

Feb 5, 2015
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Ok ladies and gentlemen, I came up with a project that hearkens back to my early days in the military. Forgive me if something similar has been posted previously, but I was unable to locate anything through the search function.

I am trying to recreate the green (jump) and red (caution) lights used by paratroopers on the inside of military aircraft, in my truck (12v). My plan is to use an On-Off-On switch to control the color being illuminated. I believe, and I have no prior experience with circuitry, and lack the terminology, that I would be running 2 sets of 2 LEDs in series, for a total of 4 LEDs. 2 reds illuminated on one half of the switch, and 2 greens illuminated on the other half of the switch.

I have read through some of the other posts, and kind of understand some of the help that has been given out. I understand that resistors will be required so as not to burn out the LEDs, and that I can run them in series as well, to get the desired result (next highest level, in combination, i.e. 555 required, but 600 will work). I also have a basic understanding of the formula to come to this determination.

These would be my questions (I have tried to place them in a logical order):

1. The power source ties directly to the "common" pole of the On-Off-On switch, where does the switch ground?

2. Where does the annode end terminate? Is this where the switch grounds? Would both series have a common ground?

3. Running them in series, the annode end of the 1st LED is wired to the cathode end of the 2nd LED?

4. Should this be a separate circuit, or would it be safe to tie into an existing one running approximately the same amperage?

5. Will the length of wire run between the switch and the terminus affect the output? If so, how would I figure the loss, and what should be done to remedy that?

6. Do I need to keep the switch amperage as close, but higher than that required for the LEDs? If the highest amperage required for the LEDs is, let's say, 2.7 amps, then a 3 amp switch would suffice?

7. Am I missing anything else?

I've attached a (very) crude schematic of what I imagine my circuit to look like, as far as I can understand it. Please feel free to attack it with your red pens. And please remember, I have zero experience in building circuits. This is completely new to me, so if you're goal is to degrade me, forget it, I don't need/want your help. If you have CONSTRUCTIVE input, I greatly welcome it, and look forward to hearing what you have to say. Again, this is new to me, so layman terms are greatly appreciated.

Thank you,
AFPara (Alex)

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2. ### pwdixon Member

Oct 11, 2012
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The positive supply goes to the common pin on the switch and the switched pins go to the resistors then to the anode/cathode to anode/cathode to earth.

I hope this is regarded as such a minor car mod that the moderators don't kill the thread for you, they don't like car mods.

Jan 15, 2015
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You would configure the LEDs like the attached and switch them using a SPDT switch (available anywhere just about) with a Center Off position. The series resistor values would be determined once the LED specifications are known. For use on automotive figure the voltage as about 13.6 or 14.0 volts when calculating for the R1 and R2 values.

4. ### wayneh Expert

Sep 9, 2010
13,435
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This may be a modification which we can't talk about, or an accessory that we can. Looking for a mod to weigh in here.
So just to confirm; the lights will always be on, the switch is just to control the color? You might consider an off switch, unless you just want to unplug them from the cigarette lighter.
The switch does not need to be grounded per se. It is part of a circuit loop that includes a path to ground, but the switch can be at any point in that circuit. "Ground" is the negative pole of the battery.
See the diagram provided. Note that the switch could be at ground instead of at the +12V supply.

The anodes of all face +12V and their cathodes all face ground. In series, the cathode of the first one in the string - the one closest to +12V - will connect to the cathode of the next one down. The cathode of the last one connects to ground. (The current limiting resistor, like the switch, can be at any point in the circuit.)

Are these generic LEDs that draw ~20mA? This is tiny compared to your automotive circuits (usually fused at 10A or more), so it can tap in anywhere. Using anything other than the accessory jack may put this thread afoul of the Terms of Service here, though.

I wouldn't be concerned, again assuming these are normal LEDs not drawing more than 50mA. If you need an amp or more, then run a fatter wire.

Uh oh. So these things are drawing that much current? I'd use a switch rated to at least 2X the known load. Would a 3A switch work for a 2.7A load? Sure, but I'd prefer a larger safety factor.

Power switch? Where will the power come from? Power on regardless of ignition switch position? Dim at night?

5. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,906
1,789
This is inside your truck? Isn't that where the pilot is supposed to sit? He does not see green and red lights. He sees indicators on his panel that read "RED" or "GREEN".

Two separate indicators, one for each color. The weird part is they are both colored green. The place I work for makes the panels, we see em all the time.

Yep, the indicator for RED is green. So is the one for GREEN.

6. ### AFPara Thread Starter New Member

Feb 5, 2015
10
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First and foremost, let me address a concern that has come up, which I feared was a possibility. This is not a modification, per se. It will not affect any safety or operational equipment. They will not be left on continuously, which is why the switch will be On-Off-On with a center off position. Essentially, this is no different than adding a prefabbed LED strip for "mood lighting". It just gets me and my boys in a different mood

Yes, ErnieM. Like I said, they are for the rear passengers, with the switch located on the dash panel for the "pilot" to alert the passengers (read: my children) The lights are located next to the paratroop doors in the aircraft, which would be simulated by the rear doors of my truck (it's a crew cab) when mounted in the B-pillar. I would love to get my hands on a couple functional pairs of actual lights, but alas I cannot find them on the interwebs, hence wanting to create my own.

Jan 15, 2015
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That's cool. What I drew in post #3 will work. Find the LEDs you want (maybe even Radio Shack) and we can figure the resistors. Radio shack likely also has the switch, just about any SPST or DPDT will work with an off center position.

Ron

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8. ### AFPara Thread Starter New Member

Feb 5, 2015
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Second, I would like to thank everyone for the time to reply. I have read, and at least made an attempt to understand, what each of you has shared with me (some of it was pretty easy, some of it not so much).

wayneh:

I would consider it more of an accessory, than a mod, as I'm not attempting to change any safety or operational function of the vehicle.

The lights will not always be on: the switch I plan to use has a center off position, with an on position on either side. One on position for red, one on position for green. I guess I should have said thirds, as there are 3 positions on the switch.

1. I believe I have an empty slot in my fuse panel. If so, I am considering making a separate circuit off that so I do not have any unnecessary power draws from any other equipment/accessories.

2. If I understand you correctly, the switch could be after the LEDs, so long as it interrupts the circuit...

3. Got it, thank you.

4. Correct, I would be using generic ~20mA diodes. If it is against ToS of the site, I can jump them off the ACC. I'm not out to get anybody in trouble for assisting.

5. Again, got it, thank you.

6. I was going off standard data found on the interwebs (and here) for values. I have to order the LEDs online, since there is nowhere in town that stocks them.

7. I would prefer to use an empty position in my fuse panel, if there is one available (I believe there is), to create it's own circuit. It will have a switch to turn them off when not in use. I know that the actual lights used in the aircraft have a ring around them that adjusts the brightness, and if I could figure out how to work a variable dimmer on each, I would like to. Another thing I thought of today, prior to reading ErnieM's response, was to install a micro LED in the switch that indicates color illuminated. Red/Green rather than the actual Green/Green he mentioned

Again, thank you all for your assistance, and if this is in violation of the ToS, my apologies. I guess it depends on one's interpretation of modification Vs. accessory.

Last edited: Feb 5, 2015
9. ### AFPara Thread Starter New Member

Feb 5, 2015
10
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Thanks Reloadron. I spent an hour in Radio Shack. No luck there. They didn't even offer to order in the stock that they were out of. They won't be getting my \$. I will have to order the LEDs and switch online.

Jan 15, 2015
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The Radio Shack of years ago died. They are in financial problems now and a darn shame too.

Ron

11. ### AFPara Thread Starter New Member

Feb 5, 2015
10
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It is sad. I'm getting into this thanks to my oldest son. He is starting to get into robotics and circuitry in a DoD partnership with city and county schools, and I want to encourage and help him as much as possible.

12. ### AFPara Thread Starter New Member

Feb 5, 2015
10
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In my original post, question #6 should have been the ~20mA as noted by ErnieM. It was late, and I'm a noob. The 2.7 I believe I was referring to at the time was volts, rather than amperage...Thanks ErnieM, I just caught my mistake. Sorry for any confusion that may have caused

13. ### wayneh Expert

Sep 9, 2010
13,435
4,272
Cool, sounds like you're on the way. Give some thought to your LED selection - there are so many! I got some really bright ones off e-bay for cheap. One reason they're so bright is the light is focused in a narrow beam like a flashlight. I think for your application you'll want a diffuser in front of the LED so that you get a big bright localized indicator, as opposed to a beam of light.

14. ### AFPara Thread Starter New Member

Feb 5, 2015
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I would prefer something with a wide angle, and of a lower intensity. However, with the variable dimmer, like a rheostat or similar, to make them brighter for daylight, and dimmer for 'night ops'.

15. ### wayneh Expert

Sep 9, 2010
13,435
4,272
For dimming, you could add another switch that chooses between 3 different resistors. It's not terribly elegant but would be quick and easy to set up. If you'd prefer a dial for continuous adjustment, there are LM317 based circuits that are pretty simple. Or, you could buy a cheap PWM dimmer on e-bay. It would do the job for just a few bucks.

16. ### AFPara Thread Starter New Member

Feb 5, 2015
10
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Surprisingly, a dial dimmer is the one thing Radio Shack has. Online.

17. ### AFPara Thread Starter New Member

Feb 5, 2015
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Possible change of plans. Let me know what you think. I am now considering running RGBs, to where the "standard" is red, but when the door opens, it would switch to green. Not sure where that would stand with ToS, as it would be tied into the door switch and the dome light. Moderator?

wayneh, are there any good topics on this in the forum, as the RS units are rather bulky/unsightly?

18. ### wayneh Expert

Sep 9, 2010
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I don't recall, because there have been so many related topics. Go take a look on e-bay for "LED dimmer" and you'll find a huge assortment. Another term to try is "PWM LED controller". I see some have built-in power on/off switches.

19. ### GopherT AAC Fanatic!

Nov 23, 2012
7,116
5,784
for automotive, it is good practice to put the switch as close to the 12V+ power supply as possible. The entire frame is ground so the goal should be to turn off as much of the wiring run as possible (bring it to ground) and minimize the chances that a vibration or broken wire will short a positive charged section of wire to ground.

20. ### wayneh Expert

Sep 9, 2010
13,435
4,272
Interesting you say that, because on my Chrysler van I've been surprised that most things are hot all the time, and turned on by completing the path to ground at the relay box or wherever the switch is. I guess they like using open-collector switches.