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Help - Simulating runway lights with LEDs

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foxenergy

New Member
I want to create runway lights for a project. I want to have 2 columns of 4 LEDs. I'd like 1 and 2 on at the same time and then 3 and 4 and so on until it repeats with 1 and 2. Can I use a 555 timer for this? Ideally I'd like to have the sequence flash quickly, but would also like to be able to adjust the frequency to slow down if need be.

Also, I want to use high brightness LED's which would have a combined drop of 28.8 Volts. Any recommendation of a small battery or other power source would be helpful. If not I guess I'll wire 4 9 volts in series.

Here is the layout of the LED's:

8 7
6 5
4 3
2 1

Any and all help is appreciated. Thank you.
 

Pommie

Well-Known Member
Most Helpful Member
Are you trying to simulate the glide slope lights or lights that run along the edge of the runway?

Mike.
 

Boncuk

New Member
Hi foxenergy,

runway lights never flash. They are steady on or off, on at night and under instrument flight conditions.

If you mean the approach sector along the final approach course 4 flashing LEDs one each side of the course won't suffice.

Further the approach course is indicated by a chain of strobes exactly positioned on the centerline.

In the touchdown zone there are double rows of lights perpendicular to the runway + an additional VASI (visual approach slope indicator, mostly used on military airfields).

Whatever you want to do, you can use a timer and a decimal counter (CD4017) to have the LEDs flash at any desired speed.

Boncuk
 
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foxenergy

New Member
Thanks Boncuk - I'll have to brush up on how airport runways are setup.

Let me modify the post:

1 - I want to have 2 columns of 4 LEDs. I'd like 1 and 2 on at the same time and then 3 and 4 and so on until it repeats with 1 and 2.

2 - Also, I want to use high brightness LED's which would have a combined drop of 28.8 Volts. Any recommendation of a small battery or other power source would be helpful. If not I guess I'll wire 4 9 volts in series.

Here is the layout of the LED's:

8 7
6 5
4 3
2 1
 

MikeMl

Well-Known Member
Most Helpful Member
What kind of LED operate at 28V? Are these some sort of clusters of LEDs like used for traffic lights, or truck brake lights? If so, how much current does each LED cluster require?

Boncuk, you must be a pilot. Your description of ALS is right on.
 

Pommie

Well-Known Member
Most Helpful Member
In the touchdown zone there are double rows of lights perpendicular to the runway + an additional VASI (visual approach slope indicator, mostly used on military airfields).
I always knew these as PAPIs - Precision Approach Path Indicators (I think). Are VASI and PAPI the same thing except VASI is military?

Mike.
 

Boncuk

New Member
I always knew these as PAPIs - Precision Approach Path Indicators (I think). Are VASI and PAPI the same thing except VASI is military?

Mike.
Hi Mike,

I think there is no technical difference between PAPI and VASI. Basically both devices are red and green lights in a box emitting the light at certain slightly overlapping angles to mix colours at an angle corresponding to the glide slope which is normally 2.5 degrees, except for mountaineous terrain where it might be up to 4 degrees.

VASI is a common term used within the NATO.

The attached sketch shows how a PAPI(VASI) works. (Sorry, Eagle has no yellow, so replace blue with yellow mentally. :D )

Please note that the accuracy increases with decreasing distance from the device. I preferred ARA (Airborne Radar Approach to PAPI(VASI) since it is independent of the weather situation.)

Regards

Hans
 

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Boncuk

New Member
8 x 3.6 = 28.8
20 ma
Something is very wrong with your calculation. You don't connect eight LEDs in series

If I got it right, you want two LEDs to light up simultaneously. Considering an LED forward voltage (Uf) of 3.6V my calculation is as follows:

2 x 3.6 = 7.2

Using a 9V (UBat) battery at an LED forward current (If) the current limiting resistor (RL) for two LEDs in series connection is calculated:

RL=(UBat-2xUf)/If
RL=(9V-2x3.6V)/0.02A
RL=90Ω

Power calculation for RL:

P(W)=UXI
P(W)=1.8Vx0.02
P=0.036W (36mW)

The next suitable resistor power value is standard 250mW.

These calculations disregard losses which will apply switching the LEDs with bipolar transistors. If using those subtract an extra of 0.7V from UBat to obain the correct value for RL.

Don't connect the LEDs to a 36V power source. You will get an extremely bright flash followed by absolute darkness when energizing the LEDs.

Boncuk
 
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gabeNC

Member
Ahhh this thread brings back memories. Went through ground school and logged some hours but never finished. What was that old rhyme?

"Red over white — you're all right, red over red — your dead."
 

Pommie

Well-Known Member
Most Helpful Member
I also remember PAPI as red and white. The only time I have ever seen it was landing in a tomahawk at Manchester international during training sessions. Shortly after that they built the second runway and banned all training flights. Shame really as hearing your second to AA55 heavy was quiet a thrill.

Mike.
 

foxenergy

New Member
Boncuk - thanks again for sticking to the thread. Yes, you're right - only 2 of the 8 LED's will be on at one time, so your calculation makes sense to me. So I would need the CD4017 and a timer? Would the 555 timer work or do I need something else?

If I'm using 8 LEDS with two on at a time I'm only to use 4 outputs (not sure of the term) of the CD4017? What do I do with the remaining six outputs?
 

Boncuk

New Member
Hi foxenergy,

of course the timer IC will work perfectly in your application.

As you can see it works perfectly in the simulation.

Just copy the schematic and wire the components as shown.

Since I like electronics cool I've added small power transistors for LED drivers. Any NPN-type will do, since the minimum collector current will never be below 100mA, of which you will use 20mA only.

What to do with the unused outputs of the counter? Easy question and easy answer: Leave them open and connect pin15 (RESET) to the count + 1 as contained in the schematic.

If you prefer a small break between cycles connect pin15 to any other of the unused outputs, e.g. connnecting it to output decimal 6 (pin5) the circuit requires two extra clock cycles to restart the LED chain.

The new value for the current limiting resistor is calculated 55Ohm considering a typical voltage drop of 0.7V between emitter and collector of the transistor. The next suitable value is 56Ohm, which is used in the circuit.

RL=(9V-7.2V-0.7)/0.02A, RL=55Ohm

Regards and happy landings.

Boncuk
 

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