Some math required I reckon....

[savage]

Lo all,

Quite a devastating project, but hopefully it will be successfull (and hopefully I'll get lots of help!! ). I want to start building scale models of air ports. Model rail roads and the like are very common these days and allot of people do them, but it recently struck me what seriously complex electronics actually is involved in running and operating multiple runways at airports - hence, I want to attempt to build them.

My first big problem (hence the post) is the current requirements. As I'm sure you all know, air ports have MASSIVE amounts of lights. Based on scale, I am estimating that 1 runway will have approximately 4,000 LEDs (DING DING DING). Up to know, I've been connecting most LEDs in parrallel, but the shocking part, is that with a 5V supply, my SPICE program reports a over 50A current for +- 100 LEDs (2.2V @ 10mA).

How on earth can I possible manage a power supply, regulators, inverters, lots of timers and allot of other electronics to drive LARGE (and I mean LARGE) amounts of LEDs? Working on 4,000 LEDs per runway, installing 2 Runways on the airport - that's 8,000 LEDs. Add some taxiways, signal lights, and the like, I think I will be easily over the 12,000 mark as far as LEDs go....

The majority of the LEDs will be RED and WHITE (which I also think isn't the best thing as far as current goes), and all the LEDs will be 3.5mm. I think as far as the runways are concerned, approximately 25% of the LEDs will be bi-coloured.

Colours used on the runways range from green, red, yellow, and white. Taxiways and the like will be Blue and White....

The bottom line, I think I need to get my hands on a KILLER power supply. So far, I thought about perhaps getting a high Amp transformer, and running a bunch (couple of 100's) of 7805's. This will give me a regulated supply of 5V 1A. My idea is then to run say 60 LEDs of each regulator... But again, I'm not sure if this will work - more than likely not.

Hopefully, someone clever here can come up with some feasable ideas for me, because I'm fresh out of ideas as far as this power supply goes, based on the ideas I get back from my SPICE modeling.......

Cheers.

 

[bmcculla]

You are probably better off buying a bunch of smaller supplies. If you check some of the suplus supply vendors like allelectronics you should be able you buy a bunch of small surplus supplies. You also should try running bigger supply voltages and using a bunch of LEDs in series. If you ran a 48V supply you could get 20 or so LEDs that could share the same current which would keep your wires down to a more manageble size - 50A would take a fair amount of copper. You also wouldn't need as many current limiting resistors. Try to stay below 60V - over 60V starts to be dangerous.

 

[jrz126]

:shock: That is a lot of LED's...

First off, I am obsessed with leds, so I'm sure I'll be able to help with this. The most I ever used was 62 ([url https://www.cardomain.com/memberpage/435572/2 [/url]). The problem with wiring them in parallel is you SHOULD have a seperate current limiting resistor for each one. This is because the LED's have properties that vary when they are manufactured, so one led could draw more current than the others and burn out.
I'd look to wire as many as possible in series. You'll need a supply greater than +5V, but it will greatly cut down on your current draw.

You should look into a switchmode powersupply, (one that doesnt use the 7805's), the 7805's burn up the extra voltage and disipate it as heat, whereas a switchmode (i think thats the name for it) supply will convert the extra voltage into usable power.

Do you have any idea of how you are going to control them?

Definitly sounds like a cool project.

 

[savage]

First off, WOW at your project... Now you are making me want to install that into my bedroom's ceiling!

To get back to business... I do agree with you that I do need to run SOME of the LEDs in series. One of the problems I have with this, is that it *might* conflict with the automation of the runway. I don't know how close you followed Bruce Willace in the Die Hard trilogy, but in one of them, he is running arround saving planes at a airport. At some stage, the terrorists take over the runways and shut them down. Did you notice the effect of HOW the runway shuts down? It is one MASSIVE Chasing LED sequence, running from the start to the end of the runway, switching of everything in parrallel. When the runway is switched on again, or reversed, the chasing effect is also reversed. This isn't going to look good - I'll draw some gifs later, but you are looking at something like this:

[pre]
1 X XX X
2 X XX X
3 X XX X
4 X XX X
5 X XX X
6 X XX X
7 X XX X
8 X XX X
9 X XX X
10 X XX X
[/pre]

Let's take the above as a small section of the middle part of the runway (the simplist part because the lights serve no other function than to be on or off.

Should the aircraft be approaching from row 10 to 1, the ENTIRE row 10 is switched of up to 1. Should the runway be reversed, the ENTIRE row 10 to 1 is switched of, and it is switched back on from row 1 to 10 (in a completely reversed sequence - the entry lights / signal lights further than row 10, now sits on the other side, further than row 1). Now, that's simple in that I can connect a entire row in series for example, but the problem comes in at the fact that towards the end of the runways (past rows 1 and 10) - the lighting gets ALLOT more complicated, and I can't simply connect a row in parrallel - unfortunately about 30 to 40% of the LEDs are situated PAST rows 1 and 10 on a active runway.

In regards to controlling the system, I am busy designing a computer based controller system that will used the printer port to control over 2048 triggers (+5V pulses) individually. This will be FAR more than I need, and I am also sure that allot of pics will be involved (something I have zero experience with so far). I was hoping to post more about this at a bit of a later stage and try to make this a "joint" project where more than one person is involved in the designing of the circuits. Due to size, the boards needs to be broken up into sections in any case.

This may be a bit of a silly question, and I admit I am asking this now without doing any research into it... What will be good values here? What will be the ideal amount of leds in series, at what supply voltage, and what is generally good values for current limiting resistors?? 100Ohm? Are there perhaps any good calculaters out there that I can use? Obviously, I won't be able to ALWAYS put 20 LEDs in series. In some cases, I may manage 20, in others I may only manage 5. Obviously, the supply voltage can't be the same. I am talking under correction, but with the LM7805's during my testing, I ran about 10 LEDs with 5V1A before they started fading...

The entire airport will be controlled by a Delphi appliction - strangly enough, the application is REMARKABLY simply to program and operate - definately not even a thought in my mind right now. The biggest problem is getting the circuit correct to allow for maximum capabilities in regards to turning LEDs (or arrays of LEDs) on or off (ala automation).

The question to ask now however, is how many LEDs in series are REQUIRED to bring the voltage down to a acceptable level to stop the LEDs from burning out and poping. I honestly doubt that there will be allot of places where I can manage to get 20 LEDs in series. Frankly speaking, are you even able to operate a "chasing" effect with LEDs in series - whilst NOT affecting the brightness of the LEDs during "normal" operation. I am aware that I can generate a "chasing" effect via the use of resistors, but these would also affect the brightness (LED1 definately won't be the same brightness as LED100 at the other side of the runway).

And wires.... Those are definately DEFINATELY DEFINATELY out of the question. I'll more than likely stick to ribbon cable for signalling and use some sort of sliding slot to connect multiple boards together SILs or something to that effect... That's one mess I most definately do not need... hehe

Again, thanks for all the feedback so far. I'm sure we're going to discuss this ALLOT in the future... I already spend hours just getting the scales right and the alignment of the LEDs to get the right amounts... If there is a interest, I'd definately appreciate some people coming aboard to help in the design and construction of the proto types... I reckon airports / meuseums, and allot of other places will definately be interested to have decent automated models of their airports built for them. (I hope) Just think of the educational benefits *g*

--
Chris

 

[savage]

Just a quick diagram of how the runway actually look. I'm sorry if this is a bit small / unclear. One pixel = 1 LED, just to give an idea of the amount of LEDs we're talking about here. The yellow arround the edges are markings and do not form part of the circuitry.

The runway at the top is for approach from the left, and bottom is approach from the right. This will also give a good indication of the whole "reversal" of the entire runway....

The arrows at the approach ends will be forming a "chasing" effect, with the arrows moving from the approach to the runway. This is done with a 555 and L297 Stepper IC - at least that part works well already

 

[TheOne]

I will seriously think of multiplexing LED's or banks to save on power.

 

[jrz126]

First off, WOW at your project... Now you are making me want to install that into my bedroom's ceiling!

Thanks

This may be a bit of a silly question, and I admit I am asking this now without doing any research into it... What will be good values here? What will be the ideal amount of leds in series, at what supply voltage, and what is generally good values for current limiting resistors?? 100Ohm? Are there perhaps any good calculaters out there that I can use? Obviously, I won't be able to ALWAYS put 20 LEDs in series. In some cases, I may manage 20, in others I may only manage 5. Obviously, the supply voltage can't be the same. I am talking under correction, but with the LM7805's during my testing, I ran about 10 LEDs with 5V1A before they started fading...

**broken link removed**
thats the one I use. It's kinda simple to calculate:
(Vsource - Vf(total))/Iled
where Vf is the forward voltage of your leds, and Iled is the current you want them to run at. so if you wanted to run 2 LED's (vF=2.2V) off your +5VDC at 10mA, it would be (5V-(2.2+2.2))/10mA =60 ohms.
If the Vf(total) is greater than your source, then the leds wont light.

The entire airport will be controlled by a Delphi appliction - strangly enough, the application is REMARKABLY simply to program and operate - definately not even a thought in my mind right now. The biggest problem is getting the circuit correct to allow for maximum capabilities in regards to turning LEDs (or arrays of LEDs) on or off (ala automation).

Shift registers will greatly increase your I/O. thats what I'm using to control the 62 individual leds in my roof. It'll take a bit more programming, but it will simplify the wiring. (you can have each shift register positioned near the leds, so you only have to run acouple wires.)

I have a schematic on my PC at work, I'll post it...tuesday is when I work again, I'll see if I can dig up an old copy of it before then.

The question to ask now however, is how many LEDs in series are REQUIRED to bring the voltage down to a acceptable level to stop the LEDs from burning out and poping. I honestly doubt that there will be allot of places where I can manage to get 20 LEDs in series. Frankly speaking, are you even able to operate a "chasing" effect with LEDs in series - whilst NOT affecting the brightness of the LEDs during "normal" operation. I am aware that I can generate a "chasing" effect via the use of resistors, but these would also affect the brightness (LED1 definately won't be the same brightness as LED100 at the other side of the runway).

The shift registers will allow you to do the chasing effect, you have to program it though.
for the larger strings of LEDs, you just have to connect more shift registers in series.

And wires.... Those are definately DEFINATELY DEFINATELY out of the question. I'll more than likely stick to ribbon cable for signalling and use some sort of sliding slot to connect multiple boards together SILs or something to that effect... That's one mess I most definately do not need... hehe

Ribbon cables and the 0.1" headers are probably your best bet.
Network cable is very cheap as well. Thats what I used for my leds in the roof.

Again, thanks for all the feedback so far. I'm sure we're going to discuss this ALLOT in the future... I already spend hours just getting the scales right and the alignment of the LEDs to get the right amounts... If there is a interest, I'd definately appreciate some people coming aboard to help in the design and construction of the proto types... I reckon airports / meuseums, and allot of other places will definately be interested to have decent automated models of their airports built for them. (I hope) Just think of the educational benefits *g*
--
Chris

Well Chris, sounds like you are very serious about doing this project. I've spent 3 months working on my LED project, I'm just getting started on the microcontroller programming for it. I'd be more than happy to share my knowledge on this.
Too bad we aren't a couple 1000 miles closer to each other. There aren't very many people that are interested in insanely large amounts of LEDs out there :wink:

 

[savage]

Only 3 months? I've just been playing with the drawings (designing the runways, airports, scales, etc) for the past six months already. My diagrams are exactly 1:75, which makes it 100% on scale with most of these plastic model planes you get that you can glue together and build... I wonder if they make a couple of 747's on 1:75 as well... *G*

The feedback I've been getting so far, has been VERY VERY helpful - believe it or not. I know I have been told to stay under 60V, but this is so neat now... 30 LEDs (RED) in series, each rated at 2V10mA. My supply is 65V. Total current rated a mere 0.06A!!!!! Vtot = 65V (Obviously), and V over each LED is 2.17V - which should be fine to ensure a long life for the LEDs.

This now means that I should be able to run 20 "bunches" (0.06 x 20 = 1.2Atot) of 30 LEDs for a total of 600 lights of one single 65V2A Supply - which is still little... At a 65V supply, I can more than likely safely use a 4A or even a 6A transformer... It's all coming together very very quickly now. I feel safe to say that the "static" LEDs (non alternating) - such as the sections in the middle of the runways, are pretty much covered.... And it wasn't even a hours work. I'm going to start feeling stupid soon for not figuring out these things myself

I don't know whether this may be usefull to anyone, but I am adapting my PC Controller interface basically from a unit I found here **broken link removed** (64 outputs). I'm not too worried about I/O really. It's not like I'm going to be switching runways on and off 10 times per second Hey... Maybe I should design a weather station as well and control the approach / runway directions with a wind sensor.... *blink*

Shift registers huh... Now there's another great idea now that you mention it... I'm already using allot of them to get the large number of outputs from my PC... I'll look into that, thanks! One thing that does come to mind is the Voltage and Current output that these registers provide. The low current may again become a problem after the registers I reckon - and no, 12,000 relays / mosfets / triacs are also not a option

 

[savage]

LIGHT BULB MOMENT! :shock:

Someone may want to just confirm this for me, but with a slight alteration in programing.....

The program and circuit (with the shift registers) that I use to interface with the PC... That entire unit only uses 1 bit of the available 8 bits on the parrallel port... Surely, with a bit of change in programming, I should be able to run another LARGE amount of registers from the 2nd data bit, the same with the 3rd, 4th, 5th, ... ??????

Or, am I missing something here??? It sure as *beep* would be easier to program this thing in Delphi than what it would be to sit and program endless amounts of PICs and stuff...

It is time for me to go get some sleep (i.e. am I dreaming), or is this actually possible????? What about introducing a series of counters??

 

[jrz126]

The low current may again become a problem after the registers I reckon - and no, 12,000 relays / mosfets / triacs are also not a option

I'm using uln2803 transistor arrays after the shift registers. They are very convienent since there are 8 i/os on them, so you only need 1 uln2803 with every shift register.

I dont know about using the parallel port. I'm not sure if it has the speed that you'll need to be shifting, it's quite slow. Also, I think you'll need more than 8 outputs.

 

[savage]

Hi,

The circuitry used for the par port uses EPP as far as I am aware. It is incredibly fast (or more than fast enough). According to the web site, it is capable of running something like 180K shifts under 1 second on a entry level P2...

I'll check up on all the info I received so far from this post and try to design a "lower" current SPICE model of the runways boards I have completed so far...

Again, thanks to everyone for being so helpful.

 

[Juglenaut]

There are some realitivly large LEDs out there, I have had one that can take 5 amps max, operate at 15-20 volts and the lens is slightly larger than the size of a quarter and has an extremly high MCD rating.

Package warns; exposure to radiation emitting from this device at very close distances to eyes or skin can cause permanent damage.

Cost might be a factor to goto larger higher voltage higher current LEDs instead of 1000's of small high MCD LEDs.

 

[pittuck]

Well rapid (http://www.rapidelectronics.co.uk) do 2mA 5mm LED's for about £0.09 each, less when more is brought. They are rated as follows:

RED - 5mcd @ 2mA - 1.7V
SUPER RED - 20mcd @ 2mA - 1.65V
GREEN 3.2mcd @ 2mA - 1.9V
YELLOW 3.2mcd @ 2mA - 1.8V

compared to a standard RED led:

RED - 5mcd @ 10mA - 2V

Which costs £0.08 each...

 

[Juglenaut]

Those arn't super bright. I am talking 10k+ MCD.

 

[Juglenaut]

Check this out, they give specs and other info as well.

**broken link removed**

conversions:

https://www.electro-tech-online.com/custompdfs/2005/01/LEDunits.pdf

Terms:

https://www.electro-tech-online.com/custompdfs/2005/01/LEDterms.pdf