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I have been fascinated by the hologram scenes in Star Wars since I was a little boy. This Halloween, I decided to create the similar effect using a home made fog screen.

Fog screen is an "immaterial" projection screen that consists of air and a little humidity, and enables high-quality projected images in thin air. The image floating in thin air encourages kids to play with it. 

However, most fog screen designs are either expensive or complicate to operate. We often need to control the temperature and the air flow at the same time. Some widely used ingredients such as dry ice and hot oil are also dangerous to kids. So I build a simple desktop fog screen for my daughter using a low cost ultrasonic humidifier. My humidifier costs $39.99. And it is the most expensive part. This process is also very straight forward. It took me about 2 hours. The operation of humidifier naturally creates the fog screen as a by-product. We do not need to think about adding dry ice or any fog solution. And my daughter loved it.

Another happy Halloween just past. Here is how I made it.

 

Step 1: What You'll Need

Ultrasonic Humidifier
Pico Projector
iPod or computer
Washing machine drain hose ( Inlet 1-1/8'' to 1-1/4'''  or 28 mm-32mm)
About 50 bendable straws
Wood photo frame (without glass) or iPad stand
Packing tape
Teflon tape (thread seal tape)

Step 2: Test and Clean Humidifier

Make sure the ultrasonic humidifier works. A typical ultrasonic humidifier uses a metal diaphragm vibrating at an ultrasonic frequency to create water droplets that silently exit the humidifier in the form of a cool fog. This forms an extremely fine mist of droplets about one micron in diameter, that is quickly evaporated into the air flow. If your humidifier has a plastic cover that is used to guide the air flow and decorate the humidifier, please remove it. We need to make our own air channel to guide the fine mist and create a thin screen in the air.  

If necessary, you can clean your old humidifier with white vinegar.

Step 3: Make a Two-hinge Bendable Straw

To generate a stable thin layer of fine mist of droplets, we need to guide the air flow from the drain hose into many small air channels. We choose to use bendable straws because they are light, flexible and easy to find.

A normal bendable straw has only one concertina-type hinge near the top, and it is still not flexible enough to guide and change the air flow. What we need is a straw with at least two hinges.

We can make a two hinge straw by connecting two normal straws with a layer of Teflon tape and a layer of regular packing tape. The purpose of using Teflon tape is to create a water proof layer between two straws and the packing tape. 
 

Step 4: Bundle Two-hinge Straws

At one end, those straws are taped together as a single layer of tubes. At the other end, they are free to bend so they can be filled in the hose. We need about 25 straws to fill the hose. 

Step 5: Connecting Hose With the Humidifier and the Straw Bundle

We insert one end of the drain hose into the humidifier opening and connect the other end with the loose end of the two-hinge straw bundle. The other end of straws are mounted on the top of the frame.

Step 6: Setup Pico Projector System and Prepare Halloween Pictures

Mount the pico projector on the table with a cell phone holder. Several Halloween theme images are saved in an iPod, which can output its video signal to the projector.

Step 7: Tuning

Turn on the humidifier, adjust the angle of straws and control the speed of air flow so that the cool mist forms a thin layer of air flow within the photo frame.

Step 8: More Images

Although we cannot walk through the fog screen at the current scale, we can touch the cool air and interact with the image. It is a great Halloween gift to kids. 

In the future, I want to create more stabled airflow by adding a little bit air pressure.
This is genius!
That is awesome. Love the idea do using the humidifier!
Oh my, this is impressive!!
Interresting concept, thanks for sharing! I cannot help but wonder whether this would be possibly to do with a whole doorframe...
Yes. We can build a very big fog screen using an industrial ultrasonic humidifier (see the link attached). <br> <br>http://youtu.be/SCjSgF3SG-Q <br> <br>
Wow! This is so cool!! What a sweet mechanism you built to project on.
Thanks. :-)

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