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Self-Contained Mini Fogging Cauldron - No Dry Ice, No Fog Fluid

Want a tiny, completely self-contained fogging cauldron only suitable for the smallest of witches? Well, read on…

While walking through a store just before St. Patrick’s Day I saw some miniature cauldron ‘pot-of-gold’ party favors. I thought, “I’m not that into St. Patrick’s Day, but these would be great for Halloween!”

Why put gold coins in these mini cauldrons when they would be great for brewing a bubbling potion?

Then, as serendipity would have it, while looking for some electronic atomizer boards, I saw a very small battery-powered, self-contained atomizer circuit board. These atomizer boards are like mini versions of the larger ultrasonic atomizers I have used to create fog before; see my Water Only Fog Machine.

The main build of this Instructable is essentially a small Fog Module that just drops into the mini plastic cauldron. This Fog Module is ideal for this mini cauldron but can be used anywhere you want a mini source of fog/smoke.

The electronic atomizer board is really the wonder of the whole project. It contains the electronics to drive the piezo atomizing disk along with a charging circuit for the lithium ion battery, LED indicators and operation timer.

Warning: Technobabble follows about why this is so cool. You can skip to the next step if so inclined.

The piezo disk (transducer) is different than the ones I have used in the past. In the past I have seen solid disks that vibrate at ultrasonic frequencies that are placed under water that cause the surface of the water to break up into fine mist (fog) droplets. These new disks have tiny (probably laser drilled) holes in them that pump super fine sprays of water when the piezo disk vibrates at ultrasonic frequencies. The disks get the water to spray from a fiber wick saturated with water that is contacting the back of the disk.

Going from seeing the plastic party favor cauldron in the store to the finished Mini Halloween Cauldron took a bit of experimenting.

I had to make sure all the components would physically fit.

I had to test the atomizer to see if it provided appropriate fog - both volume and flow. I had originally planned that I would need to provide a mini fan in the bottom the cauldron since I have seen fog stagnate and not move when using other ultrasonic atomizers (foggers). This new type of disk was so energetic that a fan was not needed.

Most installations have the piezo disk mounted horizontally and the water mist spray pointing vertically. This orientation had several problems:

A horizontal disk took up a large amount of area of the cauldron opening.

I would have to provide a deflector over the disk since I did not want the fog spray to be vertical.

If water fell back onto the disk the disk would stop spraying fog.

All of these issues were solved by mounting the disk vertically on the inside surface of the cauldron (Water Cup) and spraying the fog horizontally. It greatly simplified the design and worked great!

Now on to making a Mini Fogging Cauldron….

Supplies Needed:

- Mini Plastic Party Favor Cauldron (Dollar Tree / Amazon)
- Electronic Atomizer Circuit Board with Battery [AliExpress: “2022 New Ultrasonic Mist Maker Fogger Ceramics Discs Replacement with PCB for atomizer”]
- Fiber Wick, 10mm dia. [AliExpress: “Humidifier Filter Replacement Cotton Sponge Stick”]
- Green LED
- Fine Gauge Hookup wire
- 0.250A (250mA) pico fuse
- 330 ohm resistor
- Tiny Slide Switch, Jameco Valuepro MS22D16 Slide Switch (Jameco/Amazon)
- Solder
- Black Electrical Tape
- 1-1/4-inch diameter thin-wall PVC pipe (PVC-1120 SDR-26)
- 1/8 Inch PVC sheet (white/any) approx. 4” x 2”
- 0.2-inch (5mm) PVC sheet (black/any) scrap
- Scrap wood or plastic for button extension
- Black Felt-Tip Permanent Marker
- PVC cement
- Silicone Sealant
- Epoxy Glue
- Distilled Water

Alternate fog illuminating LED connection:

- CR2032 Lithium Coin Cell Battery
- CR2032 Battery Holder”

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