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Unity Candle

Taking the idea of a unity candle to the next level

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Some good friends are getting married, and have asked various people to help out with the wedding. They came to me with one request. To build them a "Unity Fireball" for the ceremony. This project involves creating a controllable flame effect, with focus on safety, and reliability. The flame effect portion of this project portion of this project is not encouraged, see disclaimer below. Other elements of this project can certainly be used in many other projects without issue. Specifically, the sequencing controller, prop construction and robust electrical control over long wires.

This project includes what I believe is a new innovation in the design of a propane poofer, in the use of a sequenced pre-release of propane which is not ignited. The project logs explain more about this.

A "Unity Candle" is sometimes used in a wedding to symbolize the two people coming together. Each participant uses a small lit candle, and together, they light a larger Unity Candle. Continuing this symbolism, but representing the background of this particular couple, they sought a much larger flame. A control box is located in the ceremony space to allow the couple to light the candle. It has a large firing button on the top, and key switches on the sides. They each have their own key to symbolize their joint efforts coming together. Once armed with the key, the large button becomes active to fire the candle. When fired, a 30 foot high fireball comes out of the candle itself.

Front Room Photography took this fantastic photo during the ceremony:

How the ceremony came together:  (this is not the THP entry video, see link on left for that)

See more details

If you have any questions or comments, please use the comment box below.

Project log index:

More details
How it all worked out
Installation and setup of the system on site
Wiring the system on site and being a connected device
Construction of the firing button and keyswitches
Discussion about electrical robustness in this system
Rain shield for the hot surface ignitors
Estimating the heat output and costs of operation
Additional testing of various sequence parameters
Building the decorative shell
Code running on the Arduino Micro
Added circuitry, schematics and design notes
Modifications to the controller
Reverse engineering the existing hand controller
Notes on getting the parts
Initial manual testing of the propane poofer
Mounting the ignitors
Building the relay board to drive the poofer
Assembling the propane poofer
Initial discussion of safety design
Researching details of a propane poofer and possible improvements
Researching methods of making a fireball

Disclaimer: This project should only be attempted by those who fully understand it and have appropriate training. This project information is not appropriate training which must be sought out elsewhere. Anyone attempting must comply with their local ordinances and codes.


  • 1 × Liquid Propane 20lb Tank will lasts approx 50 bursts
  • 1 × Unfilled propane tank Preferably never filled with propane
  • 2 × 3/4" solenoid valve with Viton Seals, F-NPT Rated for propane. 12VDC used, 120VAC is an alternative.
  • 1 × Pressure regulator, 100psi Rated for propane. Substitute 60psi if desired.
  • 1 × POL fitting Full bore
  • 2 × Hot Surface Ignitor, 120V
  • 1 × Hand paddle/controller Or more generically, handheld case with buttons and LCD
  • 1 × Arduino Micro Or other microcontroller.
  • 2 × Pressure gauge Rated 200psi for use with 100psi regulator. Substitute 100psi if using 60psi regulator
  • 1 × 4x8ft 2inch insulation foam sheet The pink kind, not white

View all 26 components

  • THP Entry: System Design Document, Video and Requirements

    Quinn08/21/2014 at 03:27 0 comments

    This log is intended to make clear all the entry requirement specifics in one place. Other log entries provide more details on the project and design.

    A block diagram of how it all connects is shown here: (System Design Document)

    The controller schematic is shown in this project log.

    The first prize video is also linked on the main page links, and here.

    Some comments on the contest requirements:

    This is hardware and software project where a completed functioning system will be built.

    The system is connected in that is uses a variety of interfaces to connect to a stage and lighting control system. Interfaces supported are DMX, MIDI, RS-232 serial and USB. This allows a show operator to sequence the firing with other lighting and sound effects in a performance.

    This project is being documented here, in build logs, parts lists and eventually build instructions. Schematics, software and images are provided here. Please see the extensive documentation provided in project logs.

    This project is fully open hardware and open software, with everything needed to recreate it located here on

    While the system as implemented here has safety concerns that make it an advanced project, several of the elements described are quite usable by many hackers, and can be used in a wide variety of other projects. Specifically, the sequencing controller, stage control system interfaces, prop construction and robust electrical control over long wires. Some examples of other projects could be a model rocket launch system, DIY dance lighting, and haunted house effects.

    The dual stage propane poofer is an innovative technique which can produce more voluminous fireballs with a smaller outlet size than existing poofer designs. The smaller outlet allows more economical and easily available plumbing parts to be used. No prior instances of this technique could be found in the burgeoning fire art or theater pyrotechnic communities.

    See the details section of this project above for an index to the topics covered in the many project logs.

  • More details

    Quinn06/13/2014 at 23:47 0 comments

    The ceremony control box:

    The candle in this case is 3 feet high and 12 inches wide on top of a 3 foot stone pedestal, located about 15 feet beyond the ceremony space. The pedestal is made of insulation foam, cut and screwed together, with decorative paint to make it look like stone. The backside is open to allow installation and access. The candle on top is made of a section of galvanized steel ducting with an opening in the back for installation and to allow air to flow up through the shield.

    This is actually only a decorative shell to a two stage release propane poofer. A common propane poofer releases the contents of an accumulator tank past a flame to ignite it. To increase reliability, and prevent the visibility of the open flame pilot, Hot Surface Ignitors were used. These are off the shelf parts used in the electric ignition on many gas furnaces and water heaters. A pair was used for redundancy, though in testing, a single ignitor always worked. The ignitors were mounted in a wind shield at the top of the primary accumulator output pipe which served prevent the wind from cooling the ignitor, as well as to shield the ignitors from any propane coming out of the second accumulator output pipe. The most noteworthy difference of this from most poofers is the use of a second output path that is not ignited. This allows the release of propane into the air above the poofer prior to ignition to create more of a burning fireball effect than a jet.

    The basics of a propane poofer involve a propane tank with regulator the passes "high" pressure gaseous propane and fills an accumulator tank. In this case, the accumulator is filled to 60psi.(a standard regulator for a propane grill is 0.5-1psi) The accumulator tank has a high flow path for the propane to release under the control of a solenoid valve and out the top to be ignited. A 3/4" pipe path is used here as it is the maximum output size of the easy to acquire accumulator tank, and can empty the entire tank in about 1.5-2 seconds. The poofer is fired by opening the solenoid valve which quickly releases the stored propane in the accumulator to create the fireball burst. This system of using an accumulator is required because a standard liquid propane tank has a limited rate of evaporating the liquid into gas to be released and burned. This allows high volume bursts to be released very quickly. Further discussion of the principals of a poofer is left to the reader to research elsewhere.

    The remaining part of the system is a controller which implements safety features as well as runs programmed sequences to correctly time the two solenoid valves. This was built from a surplus hand controller, with an arduino micro, additional buttons, and IO drivers and protection built in. This was designed to be very tolerant of electrical noise, spikes and electrostatic discharage without damage or incorrect operation.

    During operation, there are several safety features. At the accumulator tank, there is a ball valve which can quickly close off the output as one emergency shutdown. At the controller, removing the cable functions as another emergency shutdown. The rest of the safety factors are for the flame effect operator and located at the controller. The primary is the positive manual enable. For the system to fire, an arming button must be held, which allows the operator to continually watch for site safety, and release if there are any issues. Releasing this button will prevent firing, as well as stop and shut down any sequence that is running. This arming button only makes the system active, as the keyswitches and main button for the couple actually fires the sequence. This allows the operator to be responsible for operation and safety of the system, while allowing the couple who are not responsible for the system to fire it. The controller also implements password protection, with it locked at powerup, as well as a single button to lock it.

  • Success!

    Quinn06/13/2014 at 20:00 0 comments

    The wedding was this past weekend, and was a great success! I'll have a video, a summary and maybe some more pictures up soon, but wanted to get this out there.

    I setup bright and early in the morning, getting everything installed and ready before returning later in the day better dressed. The minister gave a great lead up to the ceremony, explaining that this unity candle was a bit different, reflecting the background of the bride and groom. The guests were mostly unaware of what exactly the unity candle was. Actually, let me just quote D:

    "To symbolize the joining of families and communities, we use the metaphor of a unity candle. Lit together, it joins two flames into one, representing lives and passions joined into one. Of course, given our bride, and our groom, our candle is a little more elaborate than some, and holds some special significance. It is represented by this box, which you probably can't see from where you are, but it has two key holes, one on each side. The key is somewhere in this room... no.(laughter) The keys represent the complex array of life experiences, of personality, of desires, and strengths, Maggie and Scott each of you bring to this relationship. Once the keys are in place, the bride and groom will, together, press the button at the center of the box, right on top. A symbol of their joint and unified purpose in their coming lives."

    The bride worked at it, and eventually managed to find the key in her dress to much chuckle from the guests. The groom simply pulled the other out of his pocket, to even more laughs. Listening to the recording is great, because from the guests you could hear quite a few shocked reactions the moment it went off, followed by an energetic round of applause, while in the video you can see the couple grinning overjoyed, chuckling to themselves :)

    Sorry it isn't a great picture, it is a screen capture from a video which wasn't the best. I'm collecting another video or two, and will see what I can put up. The photographer knew all about this, so should have some good pictures as well. I'll share some of those as well if I'm able. Actually, funny thing about that. This was kept mostly a secret from the guests, though obviously I've been putting up logs here for some time under the assumption that no one was likely to come across this. Apparently when the couple had emailed the photographer that they were going to have a "unity fireball" along with a description, she was doing her own prep research and stumbled across this log. Sure enough, "unity candle fireball" in google points right here ;)

    Overall, the bride and groom were overjoyed at how it all worked out, and the lasting memories they, as well as their family and friends will have.

    Special thanks to M&S for asking me to do this for them, to A, K and J for helping create and decorate the decorative shell, to A for hand painting the box, A and J for code reviews, to D who helped bury wires, helped with multiple setups and tear downs, and was my safety backup in case of my illness, as well as to S who helped me take everything down after the ceremony.(formal wear is not so conducive to this sort of work)

    To answer a question that was frequently asked, yes, the bride and groom did actually fire the candle flame. I stood in the wings with the controller to unlock and configure the system, as well as to hold down the positive manual enable button as long as the area was safe to launch, but the couple pressing the button actually did fire it.

View all 23 project logs

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Adam Fabio wrote 06/24/2014 at 06:01 point
Thanks for a excellent and well documented project! I'm not sure if connecting two lives will cover the "Connectivity" portion of The Hackaday Prize, But I'm happy to have your unity candle in the competition!

  Are you sure? yes | no

Quinn wrote 06/24/2014 at 21:55 point
Hi Adam, and thank you for the feedback! The connectivity aspect is probably better covered under the controllers ability to load and save firing sequences from a computer via RS232, as well as being able to integrate with a theater/DJ style lighting control system.(instead of the interconnected nature of the various elements to this project.) I had considered this portion of the prize goals, but decided to submit after Brian Benchoff's comment about what "connected" means on the blog which included the example: "A 3D printer is considered ‘connected’, even though it’s just a serial connection. The simplest answer is some sort of digital I/O."

  Are you sure? yes | no

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