My school has seniors complete a capstone project at the end of senior year. For mine, I chose to design and build my own persistence-of-vision propeller clock. I named it ProPOV.

ProPOV will have a DC fan motor, hand-etched copper-clad printed circuit board, and almost exclusively surface mount technology. I am designing the schematic and board in gEDA on Ubuntu, using the Arduino project as a starting place for the microcontroller layout and programming.

Soon I will be uploading the bill of materials and I plan to have a detailed build guide by the end of the project. See the project proposal below.

Senior Capstone Proposal: ProPOV

Abstract

For my senior capstone project, I would like to design and build a propeller clock. The propeller clock is an electronic device composed of a circuit board with LEDs (light-emitting diodes) arranged in a row, supporting microprocessor, a small electric motor, and a power supply. The propeller clock’s circuit board rotates about its center (it is the shape of a rectangular propeller blade) and flashes the LEDs at very specific frequencies. The effect of the brief, precisely timed flashes of light, combined with the rotation of the circuit board at a specific frequency, exploits the persistence of vision (POV) of the human eye to create the illusion of a continuous plane of light in the form of a clock face.

The clock will measure its rotational frequency with a Hall effect (magnetic) sensor looking for a stationary reference magnet. It will run on 12V power from a wall adapter, and transfer power from the base to the rotating board with conductive brushes. It will have white, orange, or some combination of the two colors of LEDs. It will use a DC computer cooling fan motor for rotation.

Purpose

The purpose of the project is threefold:

Creating the propeller persistence-of-vision clock (ProPOV) will require software assistance, in the form of an open-source tool called gEDA (GNU Electronic Design Automation). gEDA includes tools for schematic capture, printed circuit board layout, and circuit simulation. I would like to further my knowledge of the gEDA tool set in completing the ProPOV.

Fabricating the ProPOV from digital designs and mechanical drafts will present the second learning experience. I would like to hone my skills at surface-mount (SMT) soldering, wherein components attach to a printed circuit board (PCB) with molten solder on metal pads on the board. SMT is more difficult than the more hobbyist-friendly through-hole style of components, which have metal leads one can solder through holes in a circuit board. The SMT components will, however, allow ProPOV to have higher LED resolution (because the LEDs are physically smaller can can be placed closer together) and allow the board to be much lighter and easier to balance about its rotational axis.

Finally, I would like to complete this project because I want to experiment with programming and interacting with the finished propeller clock. Its software will allow it to display more than simple clock face designs, giving me an opportunity to design an aesthetically pleasing interface in a limited amount of time.

Potential Obstacles

The project presents numerous difficulties:

• gEDA is complicated software, not meant for beginners. I have some prior experience in using it successfully, but I will have to work hard to master it.
• I have limited time and budget, and the project requires special parts. I have preordered most of these parts, but I will need to ensure I have them all before the week of the project.
• Surface-mount soldering is difficult. I will have to be very meticulous to overcome its challenges, including burning components, melting pads off of the board, etc.
• PCB fabrication is very difficult at home. The printing of the board is perhaps the most difficult aspect of the project, besides designing it. I have practiced and will continue to practice custom fabrication methods.
• I will have to present the project in a compelling way, even if it fails. I will capture my computer activities on video, and document my build process meticulously. I will have a presentation planned even if my clock does not actually light up.

Conflicting Commitments

I am not committed to extracurriculars during capstone week.

Work Schedule

The schedule is flexible but very demanding. ProPOV will be very difficult to complete in one week. I will work six-hour days with an hour of lunch break. The day begins at 9 AM and ends at 4 PM, with lunch from noon to 1 PM. Lunch hour will provide an opportunity to get fresh air and stretch as well. I will be working at LVL1, Louisville’s downtown hackerspace.

1. Monday: Schematic design. Includes selecting components, researching connections required, and designing the logical circuit. Schematic must be finished today. Also, draft bill of materials (BOM) to ensure I have all the required components. These can be shipped overnight from Digi-Key if necessary.
2. Tuesday: PCB design. Includes designing footprints (copper shapes on the PCB) for components, routing traces (arranging the connections) and determining the physical constraints of the project.
3. Wednesday: Finalizing PCB design, and beginning fabrication. Includes printing board, drilling holes, soldering components, mounting motor.
4. Thursday: Finish fabrication. Correct (m)any circuit errors or missing traces. Check power levels before applying power. Ensure mechanical design allows for smooth, continuous rotation with little risk to components or user.
5. Friday: Write software. The software may or may not be a derivation of open-source software for a similar project, the SpokePOV (for bicycle spokes). Software will determine the final look of the clock and its behavior.

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