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LED Star Constellation Light or night light

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Picture of LED Star Constellation Light or night light
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This instructable was a small after school project that I created for some STEM Club students to make as part of our astronomy sessions. Learn about astronomy and electronics at the same time!

Materials and equipment
small cardboard box (shoe box)
Red electronics wire
Black electronics wire
5 mm White LEDs
100 ohm resistors
Small matrix circuit board
Printed picture of star constellation
Soldering iron, solder, flux
Heat/shrink wrap (optional)
9v  Switched battery holder/box
Mounting tape

 
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Step 1: Prepare the box

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Take the box and glue the picture of your chosen constellation to the bottom of the box. You may need to reprint the picture so the constellation fits nicely within the area of the bottom of the box.


Following this you need to make approx 4mm holes in the bottom of the box where the stars of your chosen constellation are located. Some constellations have only a few stars. Others have many more. I recommend a constellation with about 8 - 12 stars, but this is up to you. A 9v battery should easily power up to 20 LEDs though you may need to choose the correct resisters for your LEDs.

Step 2: Cut some wire to size

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Cut a 200mm length of red wire and black wire.

Repeat this for every  LED you are going to use in your chosen constellation. I use The Big Dipper in this instructable which has 7 main stars. So I need 7 lengths of red and 7 lengths of black.

When you have done this strip approx 5 - 10mm of insulation from the wires and twist the ends to keep the strands tidy.
randofo1 year ago
Cool. I like the big dipper. It is one of the few constellations I can always pick out for certain.
my fave is Orion.
the star Sirius is in his belt !!
Paulbacca (author)  kevinlc771 year ago
Orion is one of my favourites too! I did make an Orion light but I had to leave this at my last job.
Treknology1 year ago
You've missed an opportunity to be economical. Instead of using one LED and Resistor combination repeated in parallel, try lowering the Resistance and running some LEDs in series.

With a 9V supply rail, you should be able to get up to three LEDs in one string with a much smaller resistor, such that the 3 LEDs are using the same current as a single LED in the existing circuit.
Paulbacca (author)  Treknology1 year ago
Thanks for your feedback.

Even in parallel I'm still getting variations in the brightness of the LEDs that seems to be because of the resistors. It's a great effect.

I've never been to the southern hemisphere. So I'm in a similar position to you. Fortunately with this project you can simply turn the box up-side-down to align for northern or southern hemisphere.
What is the tolerance of your Resistors? If they're average 20%, then each could vary in value from 80 - 120R which, on high-bright LEDs, would make a distinctly visible variation in the light output. If you want higher consistency, look at better tolerance Resistors such as 5% or better. Unless you go to the ultimate extreme of 1% tolerance, there will still be noticeable variance, and I suggest you re-arrange the LEDs according to the magnitudes of the stars they are representing (as it looks to me in the photo).

As NitroRustlerDriver points out, when a LED fails it is usually a short circuit rather than open circuit.

<03:00 rant>I am working on my own LED lighting design to get the optimum wattage:efficiency ratio. On the last batch of LEDs my calculation was 80 minimum in a single string to handle 260V peaks in Oz at a rating of about 5W. I don't want lower power using chopper supplies because of RFI health risks, and I definitely don't want to use Luxeons because they are really pushed to the limit and with those whopping great heatsinks on them, where's the so-called efficiency improvement? So I'm looking for a comfortable balance which will probably be a 10*10 square to allow for higher spikes, and hopefully enough buffer, so that if one LED shorts it won't overload others. I'm also trying to come up with a design that is extremely easy to unplug so that defective LEDs can be replaced without excessive diagnosis. That safety barrier probably means it will only operate at about 4W (over-engineering rears its ugly head again). I'm designing it to plug directly into the wall, in such a way as it MUST be physically removed to replace any defective LEDs which, if I get it right, should be a fairly quick process.

If you want a challenge, mount 5mm multicolor LEDs in a practice golf-ball---works fine until you want to fit a battery inside. As this was part of a movie prop, I'll put both related projects up at some later stage. I'm not going to get photos together in time to get an entry this time.

I love to support simple starter projects like this, because this is the learning field before you move on to sticking your fingers inside live mains equipment and taking your life into your own hands. I was lucky. My Father was an electrician and Installation Inspector. From very junior ages (5-6), I was allowed to wire up mains equipment, provided that he inspected it before it was plugged in, so by my early teens 240V zaps were a way of life. Sadly I grew up in old 3-phase territory where Red Yellow and Blue were the primary (colors) phases, Black was Neutral, and Green was Ground. Changing over to the new ISO standard was annoying, but when I look back on it, it was designed with two major factors in mind.
One, Red-Green Color-blindness (the most common, leading to Active/Earth swaps).
Two: Such color-blindness is prevalent in males who predominated the industry at the time.
This will work, but you will get much more even lighting from the LED's by putting a resistor on each one. Manufacturing variations in them cause them to draw different amounts of current, so when wired in series, some will draw less current and be dimmer then others. Also, when wired in series, if one burns out, that will increase the current draw on the other LED's, possibly causing them to burn out as well.

All in all, it is much better practice to wire them in parallel, each with their own resistor.
I get your point but, are not these LEDs meant to be of varying brightness to represent star magnitude? Or is that just the way it happens in the photography? Being in the Southern Hemisphere means I've only seen representations of the "Big Dipper" and never the real thing.

I would expect that if a LED were to fail, it would happen within the first week. It is only because of over-driving illumination LEDs that there is even a quoted life-span on LED products.

I'm also very prone to over-engineering, meaning that I would be running the LEDs below their peak values and seeking to make that 9V battery last to the bitter end. If using a potentially spiky power supply from the mains, then, yes, I would defer to your preference for individual resistors.
LEDs don't get short-circuited when they burn out; they only get dimmer, or open-circuit in catastrophic cases.
I would follow Treknologys design advice :) , not too difficult to test both designs before committing yourself either.
wilgubeast1 year ago
Nice. Oh man, there are so many more constellations that could use the night light treatment. Somebody's got to get their scout troop or physics class to make a full night sky's worth of these. Start with the northern hemisphere, then later... the world!
Remember that the those constellations that can be seen in both hemispheres are upside-down to each other.
Paulbacca (author)  wilgubeast1 year ago
Thanks. Actually I did a large version with a large paper mâché dome and Christmas lights. It worked great but I did not take any photos record the build. That would be an awesome next project for me to do again for instructables.

I love LED projects - this one is pretty nice dude.

there is a few on my site, one popular one is the knightrider/cylon LED scanner on stripboard HERE
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