This project is targeted towards the K-3rd grade crowd. There are a few initial steps that an adult has to do to prepare, but after that, it's completely kid friendly.
A couple of Halloweens ago, I saw a house with a ghost with LED eyes hanging in the tree by the driveway. I thought it was cute, so I peeked under the sheet. It was two LEDs taped to a 3V coin cell battery. Not exciting, but certainly effective. This year, as an excuse to play with electronics with my kids, I pulled that idea back out and gave it a major overhaul. This project was the result. We liked it so much that we bought a bunch of parts and did it as a group with my daughter's Brownie Girl Scout troop, where we had a 100% success rate with limited adult assistance.
This project requires the following supplies:
- 18oz Crystal Geyser water bottle
- 2 matching 3V LEDs
- 1 150 Ohm or 250 Ohm resistor (see below)
- 1 bat switch (on-on or on-off)
- 1 terminal block trimmed down to 5 terminal pairs
- 1 9V battery snap
- 1 9V battery
- A 20"x20" piece of light, white fabric (e.g. poly-cotton)
- 1 4" zip tie
- Small flathead screwdriver
- Lead-free solder
- Wire stripper
The last four items are for the adult prep steps.
The size of the resistor depends on the LEDs. If your LEDs are rated around 3V, then a 150 Ohm resistor is fine. If you have 2V LEDs, then go with 250 Ohm. (The red LEDs tend to be 2V.)
Any small water bottle will do, but I think the Crystal Geyser bottles have just the right shape for this project.
These are the parts I used:
My total cost of supplies was about $6 per ghost.
Step 1: Do the Adult Things
Before you get the kiddies involved, there are two things you need to prepare for them.
First, you'll need to solder two 4" wire leads onto the switch. The goal is to have the switch control whether connection between the leads is open or closed. If you have an on-on switch with a third post, you can just ignore that post. Make sure you strip both ends of the leads.
Second, you'll need to drill some holes in the bottle. You'll probably want to drill five holes:
- A 1/4" hole just above the line where the bottle goes from being cylindrical to being conical
- A 1/8" hole just above the line where the bottom attaches, on the same side as the first hole
- A 1/4" hole somewhere between the first two holes
- Two 1/16" holes in the bottom of the bottle
The first hole will be to house the switch. Most switches have a 3/16" post, but I find that if you drill a 3/16" hole, it's too hard for kids to get the switch through. A 1/4" hole makes it easier, and it's still small enough for the switch to screw onto. Make sure to clear away any flashing from around the hole, because it will get in the way of attaching the switch later.
The second hole is for the zip tie to hold the terminal block in.
The third hole is just a starting point for the cutting they'll need to do. Getting a hole started in the bottle with a pair of scissors is a little risky, even for an adult.
The last two holes are to run a string through for hanging. The other three holes will be on the back of the ghost, so these two holes should be to the left and right of the center of the bottom so that the ghost faces forward when you hang it. Exactness is not required.
Step 2: Assemble the Eyes
You can see from the picture above how the components should connect. It is important to connect the LEDs both with the longer lead to the left. The leads should not poke all the way through the terminal block. They should only go far enough in to make a firm connection. I find it's easier to tighten the terminals down most of the way before inserting the leads. Just don't tighten them down so much that the leads won't fit in.
Through the terminal block, the first LED connects to the resistor connects to the second LED connects to the switch connects to the battery snap connects back to the first LED. Make sure that the red lead of the battery snap connects to the terminal opposite the first LED, and the black lead connects to the terminal opposite the switch. Screw all the terminals down firmly so that none of the components wiggle. It's best if the leads are under the screws in the terminal block instead of beside them.
As long as both LEDs face the same way, you can face them either direction, but if you put the longer lead on the right, you'll need to swap the terminals for the red and black leads of the battery snap. If you end up with LEDs that don't both face the same direction and/or don't agree with the terminal snap, the circuit won't work.
Step 3: Test the Circuit
Now comes the moment of truth. Connect the battery to the battery snap. If the LEDs don't light up, flip the switch. If they still don't light up, disconnect the LEDs from the terminal block and make sure they're both facing the same direction. Also make sure the red lead of the battery snap connects to the same end of the terminal block as the side of the LED with the longer lead.
Once you've verified that the circuit works and that the switch controls it, bend the two LEDs towards the top of the terminal block so that they will point forward when you install them into the bottle.
Step 4: Prep the Bottle
In order to get all the stuff into the bottle, you'll need to cut a hole. I recommend a rectangular window that starts about 2/3 the width of the terminal block below the hole for the zip tie, stops above the hole for the switch, and covers about 1/3 of the bottle's circumference. Use the starter hole to get going.
Step 5: Add the Sheet
Once you have the terminal block installed, it will be difficult to do much inside the bottle, so it's best to attach the fabric sheet now. There are two approaches that work. You can either cut two small slits in the fabric or thread a needle with the string. Either way, thread the string through the fabric, into the bottle through one of the holes in the bottom, out through the other hole, and then back through the fabric. Since you are attaching the sheet to the bottle, you'll want the string to go through the sheet somewhere near the middle, roughly aligned with the holes in the bottom of the bottle. After the string is threaded through, tie the two ends of the string together. A square knot works well.
Step 6: Install the Terminal Block
Insert the zip tie through the hole in the bottle. Place the terminal block into the bottle so that the zip tie falls between the two LEDs. Feed the zip tie through the loop made by the resistor. Make sure everything is roughly in place and then close the zip tie and pull it snug. The LEDs should be roughly level. You can always make adjustments later by bending the LEDs. This step is probably easiest to do if you disconnect the battery first.
Step 7: Install the Switch
Remove the top nut and washer from the switch. Poke the switch through the switch hole and replace the washer and nut. Turn the switch so that the bat handle operates on the vertical plane (up and down). Tighten the nut. Finger tight is fine.
If you find that the post isn't long enough to go through the bottle and still let the washer and nut go on, make sure that there isn't some flashing left over from drilling the hole that's getting in the way. Worst case scenario, you can leave off one or both washers.
Step 8: Hang It Up!
Reconnect the battery and drop it into the neck of the bottle. Drape the sheet down over the bottle while holding it by the string loop. Make sure the strings are not twisted between the sheet and the bottle. Turn on the switch and hang it up!