This project was inspired by a co-worker and is a great exercise to work on your soldering skills. I made a constellation light for my daughter. You could easily adjust this project to suit your own horoscope project. I suggest not making the lights as bright. Later on in the project I described some possible improvements on this project.
Materials Needed for this project:
- 2' x 2' wooden board
- White LED
- Resistors (Its value is figured out by http://led.linear1.org/led.wiz)
- Power source (USB wall wart or similar)
- Wire stripper/cutter
- Hot glue
- Mineral Spirits
- Soldering gun
Step 1: Step 1: Transfer the Horoscope
Find a a picture of your horoscope. I am using one an enlarged version of one found online. The photo needs to be printed in reverse onto to a large piece of paper. Be sure to leave some space on the margins. Take the printed image and place it on the wooden board. This wooden board or picture frame was found at Michael's craft store. The image is transferred from printed paper to wood by placing it on the board, image down. Using mineral spirits, sponge the paper and lift the paper up. The image should now be on the board.
Apply some varnish or lacquer to seal the image on the board.
Step 2: Step 2: Adding Holes
For the "stars" to shine through, I needed to drill holes into the board. Depending on your constellation and photo you choose to use, you will have a different number of stars to make. One option is to only light up a few of the stars. I adjusted the size of the drill hole to control the brightness. The brightness can also be controlled by angling the LED in its whole since less light comes from the side of an LED than straight out of the top.
First, I drilled holes for the opening at the front of the picture frame. This ensures any splintering happens out of view. Drilling onto a hard surface, like a block of wood, also helps minimize splintering.
At the back, I added a counter-sink using a drill bit the same size as my LEDs. This helps hold the LED in place when it gets hot glued.
Step 3: Step 3: Adding LEDs
This is an afterthought, but it would be better to solder the resistor to the LED before they get mounted. It makes a bulk of the soldering much easier. Handling of the resistors is in the next step.
Place the LEDs into their holes. Be careful with the angle of the LED. They are very directional lights. Some LEDs only give out light at 20 degrees from the top. So unless you are almost looking directly down, the light will seem very dim, where from the top is actually uncomfortable to look at.
I rotated the legs of the LED so the longest leg (positive, anode) is relatively close to other LEDs anodes. This will allow me to solder them in clusters. To avoid any confusion later on, I bent all the shorter (negative, ground, cathode) legs. I suggest bending them with pliers to get a smooth bend. They can easily snap off. Use hot glue liberally to hold the LED into place.
Step 4: Step 4: Power
I used a wall wart from an old cellphone charger to power the project. It's output is 5V (DC) at 1500 mA (1.5A). This is ample power for all of my LEDs. Now I need to figure out the current-limiting resistors.
I used an a online calculator though you could quickly figure this out using Ohm's Law. The supply voltage is 5V. I assume the forward voltage for an LED is 2V and its forward current is 15 mA. I had 53 LEDs in my array but this won't affect the resistor value.
If you want the LEDs to be less bright input a lower current (e.g. 10 mA) and you may be able to go as low as 6 mA depending on the LED. Please note that different coloured LEDs have different characteristics. Try it out on a solderless breadboard first to see that your circuit is the brightness that you are looking for.
Without these resistors, the LED is toast in a bright blink. Each LED needs to have a resistor as well since all LEDs are not exactly the same. Some have a slightly lower internal resistance and thus will draw more current. If only one resistor drove a cluster of LEDs, one of them would draw the lion's share of current and burn out more quickly. The same would happen with the next lowest LED until all of your LEDs have burnt out.
To prepare the wall wart as a power source, I made sure it wasn't plugged in and I cut off the USB end and striped back the wire about 2 inches to expose four smaller wires. The red and black, positive and ground respectively, are the ones we want. The other two are for serial data and we don't need them. Cut them back to leave only two 2 inch long red and black wires. Strip each write to give yourself 1 inch of exposed wire.
Step 5: Step 5: Soldering the Resistors
First, lets be clear about Resistors and LEDs. Resistors are bi-directional so it doesn't matter what side is connected. LEDs are Light Emitting Diodes and being a diode they are one directional. If an LED is not connected properly, it will not work.
I soldered the two components together by adding a bit of solder to one leg of the resistor and to the anode (positive, long) leg of the LED. Using pliers to hold the resistor, put the two legs together and heat them with a solder gun. The solder from both will melt and bridge between the two. Its not the ideal joint, but it works well in tight spaces.
Step 6: Step 6: Connect the Positive and Ground
I soldered the positive connections together first. Clusters of positive connections where formed where possible to limit the amount of additional soldering to be done and wires added to make sure all the clusters were connected together and finally to the positive (red) wire from the power supply. I trimmed any extra parts of the legs or wire to keep my connections neat, ensure there were no shorts and check that all joints had been soldered.
Afterwards, I connected all the ground (cathode, short) legs of the LEDs together by soldering individual wires. Once again, I trimmed all the extra bits of the legs to ensure no shorts and all connections were soldered.
Step 7: Step 7: Final Prep
I checked over everything inside one more time to make sure there were no shorts. There are a lot of exposed connections and I needed to be sure there were no left over bits of cut wire or legs floating around. I plugged in the project and carefully checked that there were no shorts and that all the lights worked.
Finally, I used a bent nail to hold the power wire in place. That way, if someone pulls on the wire, it will pull the frame off and not tear the soldered connections.
Overall, I am pretty happy with this project, though I found 53 lights at 15 mA a bit bright and I would opted for 10 mA limit in future. I hope to expand this project to work with a nightlight circuit so it only turns on when its dark or possibly turn this into an Arduino project. Another improvement would be a hole drilled into the bottom of the frame for the power supply to go through. The hole would allow the frame to mount flush with the wall. If you are worried about the exposed connections, you could paint them with acrylic paint which is not conductive and this will isolate all your connections.
Please send me any comments or feedback. This is my first instructable and I would love to make it better!