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
Step 1: Prepare the Box
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
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.
Step 3: Tinning the Wires
PLEASE BE CAREFUL WHEN SOLDERING. BURNING YOURSELF IS POSSIBLE IF YOU DO NOT TAKE DUE CARE.
Next we need to tin the wires. This means we are going to coat the ends of the wires with some solder. This makes it easier to solder the wires to the LEDs and circuit board and also keeps the wire strands tidy.
To do this coat the bare ends of the wire with some flux. Then with a hot soldering iron pick up some solder and then draw the melted solder along the bare wire. Repeat this on all wires.
If you have not done any soldering before, you may need to check out a good guide. There are a few on instructables. Try this one: https://www.instructables.com/id/How-to-solder/
Step 4: Solder the Wires to LEDs
Before we solder the wires, you need to know which wires, red or black are soldered to the correct part of the LED. Anode (+) or cathode (-). You can determine this by looking for the flat edge of the LED. This is the negative terminal. It is also the shorter of the two terminals.
cathode (-) = black.
Anode (+) = red.
Solder the black wire to the cathode (-) and the red wire two the anode (+). You may want to shorten the LED terminals to about 10mm to match the wires ends
Try to make the soldering as neat as possible so that you can slip some shrink wrap over the soldered connections. Once heated with the soldering iron it will shrink to insulate and hold the connection together. This is optional, though you must make sure the + or - do not touch.
You will need to repeat the tinning and soldering for the number of LEDs your chosen constellation has. I have chosen Ursa Major (The Big Dipper) which had 7 major stars. Therefore I need 7 pairs of tinned red/black wires.
Solder the wires to the Remaining LEDs and shrink wrap soldered connections if desired.
Step 5: Create the Circuit Board
The circuit board is used to connect the LEDs to the power source. It is good practice to use resistors to maintain the correct amount of power to the LEDs. Otherwise the LEDs might blow. It is not advisable to do this project without resistors.
This circuit diagram shows 7 LEDs. The LEDs are in parallel layout with a resistor of 100ohms. The LEDs wil be quite bright with 100ohms.
Take your piece of circuit board and place the resistors like this image. It does not matter which way you place the resistors. All components are placed on the non copper side. All soldering is done on the copper side. The copper helps the solder adhere to the circuit board.
Solder these on the reverse side being careful to solder to that copper strip only.
Trim any excess off of the resistors leaving a nice clean soldered join.
In this picture you can see I've added some additional wire to connect the resistors in parallel.
Step 6: Solder LEDs to Circuit Board
Next we want to solder the LED wires to the circuit board.
Place the black wire from one of the LEDs in the hole next to a resistor. Solder this in place so that it is connected to the resistor.
Place the red wire a few rows up from where the black wire is. Solder this in place
Repeat with the remaining LED wires making sure that the red wires are all in the same row and the black wires are soldered to the resistors.
You may also need to solder joins in the row of red wires to make them parallel.
Step 7: Add the Switched Battery Box
Solder the red wire from the battery box to the row of red wires or the positive terminal.
Solder the black wire from the battery box to the bottom row by the resistors or the negative terminal.
Put a 9v battery in and test it works.
Step 8: Insert LEDs
Gently insert the LEDs into the holes from the inside of the box until you can bed or wedge the LED into the box. Do this for all LEDs.
Finally, use some double-sided mounting tape to secure battery pack and the circuit board to the box.