Week 15, System Integration

Individual assignment:: Design and document the system integration for your final project

Cromira

My final project, Cromira, is a lens mounted photo tool that allows the user to produce three different effects, custom shape and color vignettes, prismatic projections and prismatic flares.

I have been exploring how to achieve all 3 of these effects through both assignments and individual exploration and it is ready to be brought together as a final project.

The development from here will be documented on this page

Features/ Technical Debt

The device will lock onto a Sony 50mm fixed focal length lens where the camera hood normally mounts. This alternative hood will allow for the creation of all the different effects. Generally, all 3 features have been explored and are working to varying degrees. The design and packaging of the device has also been explored in depth.

Custom Color and Shape Vignettes

This was explored heavily during Week13, molding week and is working great. This will be achieved by shooting light from side mount addressable LEDs through an overmolded silicone sleeve. This feature will be achieved with removable lens hood that will magnet onto the front of Cromira and connect to power and XIAO through a 3-pin connector.

Prismatic Projections

This feature has been the hardest to do well. I have been exploring a bunch of different diffraction grating and LED options. From that exploration the bast way to implement it is to have white LEDs shine perpendicular to the axis of the lens and shine at pieces of CDs that are at approximately 45 degrees to the light so that the diffraction is directed at the subject of the photo. I have had a difficult time finding a good LED for this as Neopixels and RGBs do not have as full of spectrum as white LEDs and do not diffract well. I have found some flashlights that work well, but the brightness can be an issue for the subject of the photo.

This feature will be built into the device and will have doors in the side of Cromira that the user can open to allow the light to get out of the device and diffract off of the CD. I will also build brightness adjustment into the app to control the saturation of the projections.

Prismatic Flares

Prismatic flares are easy to achieve as they just require a piece of diffration grating to be placed over the lens. I have exlored this more in the last week with good results. My strategy here is to make a couple of diffrent diffraction grating options that will magnet onto the front of the device and will be able to rotate around the axis of Cromira. This will allow the user to change the way that they want the rainbow light effect to influence their shot.

In my research it is difficult to make custom diffraction gratings in the lab, so these will be purchased and built into the device.

System Integration

To make all of these effects, appropriate technology had to be hired to make it happen. The requires a combination of mechanical, electrical, and software elements working in concert.

Mechanical

The device will be made from a series of plastic and silicone parts. The main housings will be 3D printed using black resin from a Form4 machine and sanded and clear coated for a quality finish. The vignette ring will be a resin print that is overmolded with silicone to encapsulate the LEDs.

The device will use magnets on the front of the main housing to keep the vignette and the prismatic flare rings on the device. There will be doors on each side of the main housing that will expose the LEDs and diffraction grating for the prismatic projections.

CAD of the side door that the user can open to make prismatic projections. There will be a piece of CD on the inside of the door and a high power LED inside.

Electronics

I am using a microcontroller and series of supporting electronics to build Cromira. The main components are outlined below.

Microcontroller

Throughout this class, I have used the XIAO ESP32 C3 to build prototypes of the lighting effects and to build apps. It has Bluetooth connectivity which I need for my app and has also proven to drive both addressable and high power LEDs without any trouble. I have used it over and over in most of my prototypes and will use it as the computing backbone of my device.

LEDS

For the vignette tool I am using a strip of side-emitting addressable LEDs from Adafruit. These are small and similar to the 2020 addressables that I have used for my overmolded prototype in Week 13. I opted for side-emitting LEDs as I can wrap them around the circumference of my device and shine them through the silicone. It will be a more elegant packaging than the standard strips I used in molding week.

I have not locked into a white LED for the prismatic projections. I have had good success making good rainbows with small 400 lumen flashlights that I have around the house. However, I have tried to use Adafruit high power RGBW neopixels and they did practically nothing. I have about 3 or 4 options of high power white LEDs that run off of 5V or less and have between 200 and 400 lumens. I will pick one from this bunch that has the best rainbow making quality and is easist to drive. I may have to design a mosfet driver circuit to make this work.

Battery

The battery choice is a tricky one as the device has the potential to draw a lot of power. The maximum current draw for the side emitters (.27 meters to wrap around the device) is .80 amps at full white and brightness. Some of the white LEDs I am looking at are .7A. However, from my packaging restraints (see below) I do not have much room for high capacity batteries. Right now I have decided to test out two, 20C 150mAh batteries wired in parallel for a total capacity of 300mAh. Each battery will be able to deliver a continuous 3A (20C x .15A). So this should be enough overhead to run them. I plan on using the charging circuit on the XIAO, but this needs to be tested.

App

The device will have a companion app to control the LEDs. This was explored and half completed in Week 14. It is built in MIT App Inventor and runs only on Android. It will have one function to send custom mixed colors to the vignette tool and a seperate function to turn on and control the brightness of the white LEDs for the prismatic projections.

Rough diagram of the app showing the 2 different modes.

Working app that can change the colors of the vignette ring.

Design

I did a design exploration to see how the product might look. Since the product is beign built around a cylindrical camera lens, it was obvious to keep a cylindrical profile. This shape both references the shape of the lens and is also easy for the photographer to use. The cylinder shape does pose some packaging challenges that will be discussed more below, as it is difficult to package rectilinear components like batteries effectively in this shape.

Early sketch exploration trying to work out how a door would hinge open for the prismatic projections and working on the silicone snoot for the vignettes.

Another challenge was to allow the photographer to change between these effects in an easy way. For example, I did not want the vignette tool to be in the way if someone wanted to use the prismatic projection function. During my sketching I found that I could separate the device into a main housing with the bulk of the components and have the vignette and flare tools magnet onto the front of the body of the device.

Sketch exploration of using magnets to change between tools

I briefly explored an octagonal shape to have some flat surfaces to mount things to. However, I dismissed this quickly as it looked bulky and I was worried about the sharp edges being a distraction.

Then I pulled together a sketch that embodied the cylindrical design that I wanted to have with integrated features. I gave it a sort of apple-like shape to leave room for electronics and mechanisms, and had it taper down to a sort of duck bill shape for the vignettes.

Sketch showing a cross section of the cylindrical cross section with some rough packaging elements shown like the batteries.

After my sketching, I explored the shape in SolidWorks and roughed out the shapes. Generally, I liked how this looked and felt confident taking it forward into the packaging exploration.

Initial CAD work pulling together the overall shape of the device and separating the parts into thin walled parts. This shows both the vignette tool (duck lips) and the prismatic flare tool (scalloped ring) in place. However, in practice only one would be used at a time.

Cross section view of the same CAD. While the device will not be injection molded, I wanted to generally use principles of injection molding design like using consistent wall thickness and respecting the pull direction of the mold.

3D print to test fit of the device and to make sure the cutout was big enough to turn the focus ring, which it was.

Packaging

The goal for the packaging exercise is to make sure everything will fit inside of the shape conteplated in the design sketches.

Main Body

The main body of the device will house most of the core elements included the microcontroller and its PCB, the batteries, and the high power white LEDs. The batteries were the hardest component to place inside the device as I wanted to have the most capacity possible but had to keep them small enough for the rectangular shape to fit inside the cylinder. While curved Lipos are available, the lead time and cost are too prohibitive for the device at this time.

Through conversations with other people in my lab, I realized I could use the area over the focussing ring to extend the amount of room for components. The downside to this is that I still wanted to have finger access to the focus ring incase I still wanted to use manual focus. So, I was able to carve out a few millimeter area on the bottom of the housing so I could still use my middle finger to rotate the ring.

Since the XIAO is small, I was then able to fit it and a rigid PCB on the bottom of the cylinder. Then I placed the batteries at the top of the device where there is more room and still keep them out of the way of the white LEDs that need to go on the side of the housing.

CAD cross section showing the XIAO at the bottom of the device and the battery at the top. Note that the bottom of the housing is cut out to allow for access to the manual focus ring.

Working on the XIAO location with an early 3D printed prototype.

I wanted to have access to the USBC port of the XIAO so that I could plug it in for charging. Fortunately, I was able to carve out a rectangular hole at the bottom of the device for access.

Testing the fit of the USBC with a 3DP prototype.

Vignette Ring

A key challenge was to make the interation of the vignette ring and the main body elegant. I opted to create a channel at the front of the device that the ring could slip into. Then I will add magnets to both the vignette ring and the main device and hold it in place. A 3 pin connector will provide electrical connection to the addressable LEDs on the ring. The female side will be on the XIAO PCB with the male side protruding from the ring side.

3D printed prototype with connector hot glued into it to test the fit.

3D print of the LED ring with the male connectors used to test.

Flare Lens

I was then able to use the same channel to mount the flare lens. I created a ring that will hold the diffraction grating. Then there will be a thin steel ring bonded inside the 3D print that will magnetically attached to the main housing with the magnets housed inside it. This concept was tested with FDM prints without the magnets and showed promise.