For this assignment, you have a choice between designing and fabricating a printed circuit board (PCB) or an enclosure for your pico pro microcontroller. For the enclosure, the look and feel is open ended - what's important is that it securely holds and protects your components. For the PCB, the purpose of the board is open ended, but the use of surface mount passive components is recommended (this will likely make your fabrication process much easier).
The enclosures can be 3D printed at Jacobs Hall. The PCBs can be milled out using the Othermills in 110/120 Jacob or the LPKF S63 in the Invention Lab (Sutardja Dai Hall).
Though not required, this could be an opportunity to begin to make progress on your final project. For example, if your project needs a camera, make a first iteration of an enclosure with mounting holes for your camera. If your project needs a particular sensor, make a breakout board to test that sensor.
If you are a complete novice or already an expert at using the design software (circuit or mechanical CAD), you should pair up into novice/expert teams and complete this assignment in groups of two. If you’ve had a little experience with the design software, but would like to gain more exposure, you may also attempt this assignment on your own.
Use a top down modelling approach to create your enclosure. A model or sketch of the microcontroller can be used as the driving geometry for the top down model. (overview of top down design. For Solidworks, but similar idea in Fusion)
- The parts should fit securely inside and not be free-floating such that if someone dropped the enclosure, its contents would not move around.
- The container should be made up of a top and a bottom piece. The two pieces should be shells and mate together cleanly with no protrusions at the seam.
- Use bosses and fasteners to attach components to the enclosure, and to join the two halves.
- Fasteners in plastic: self tapping plastic screws work well (e.g. fastener for antenna flange). Machine screws (e.g. #4-40s) will also work in a pinch, though the fine threads will not be as robust. Machine screws can be used reliably with heat set thread inserts.
- The container should have a cut-out that allows you to plug a USB cable into the board.
- The pico-pro microcontroller shares a similar form factor to the Raspberry Pi. Models for the Raspberry Pi can be found online, and can be used as a starting point for creating a simple model of the pico-pro for checking clearances, etc. Feel free to download and utilize relevant parts from online resources such as grabcad.com.
- Position the cutout at or between the seam to avoid undercuts that manifest as overhangs when 3D printing, or additional side pulls/cam actions when injection molding.
- Make sure you measure the USB cable - depending on how far you have to insert the plug into the box, your cut-out may have to be bigger than the metal USB connector itself to account for the entire plug.
- Use Mcmaster to find fasteners. CAD files can be downloaded from Mcmaster to check for clearances, etc.
- We have extra Plastite fasteners: https://www.mcmaster.com/#90380A108
- Create a dimensioned drawing for the top and bottom piece of the container with overall dimensions. Do not worry about dimensioning small features inside. Include the front, right and top views in your drawings.
- Create a front, right and top view drawing of your final assembly.
- Be able to open and close the box without a screwdriver: hinges, snap fits, printed threads, magnets, etc. Features can either be printed or off-the-shelf parts.
- Pretend you are prototyping for an injection molded part. Maintain thin, consistent wall thicknesses, add gussets/webbing for increased stiffness.
- Modify ergonomics to make the enclosure handheld
- Add user facing buttons (e.g. access the reset button from outside the enclosure)
- Add an internal battery holder and battery (e.g., 3.7V LiPo).
- Use something other than an FDM 3D printer.
- CNC your enclosure out of aluminum, Macbook Pro style.
- CNC polypropylene and prototype living hinges
- Prototype overmolding with the Objet multi-material 3D printer
- Tell us who is in your group if you are submitting as a group.
- Submit your design files and screenshots of your design
- For Fusion: submit your Fusion part and drawing file by sharing a public link of your design file with us
- For other CAD, share a zip file of the model files
- Describe the process and strategy you employed to model the different parts and to fit them together (1-2 paragraphs)
- Include pictures of the printed enclosure. At a minimum show the two halves separate, two halves assembled, and a closeup of the usb connector passing through the enclosure.
Starting files: https://berkeley.box.com/v/IDDeagleLibrary
Make a pico-pro hat to test a component you are considering for your final project. If none come to mind, create a pico-pro hat for the ADS1015. The design does not need to be the size of an entire HAT.
Order components early
Ask us about the component you want to test. We may have a similar one on hand. We have extra ADS1015 chips as well as 2x20 pin headers.
The electronics lab has many surface mount passives in various packages.
Many components can be sampled for free from Texas Instruments: http://www.ti.com/general/docs/gencontent.tsp?contentId=69854 (ETA 4-5 business days)
Eagle Library Component
If a library component does not exist for the IC you wish to test, follow the instructions here for adding a new component in the library.
Schematic and Layout
- Create a schematic for your PCB.
- Maintain legibility by labeling nets rather than wiring everything directly.
- If you are making a full HAT for the pico pro, add correctly spaced holes for fasteners
- Make sure your board passes the design rule check (DRC) for the machine you are using before fabricating
- Go through the following checklist before fabricating
- Are there any potential mechanical interferences between your board and the pico pro board (especially underneath the board)
- None of the holes will be through hole plated. Which side do the through hole components need to be soldered from?
Fabrication and testing
- Get trained on the Othermills at Jacobs or the LPKF at the Invention Lab.
- Fabricate your board. Make more than one if possible, to account for soldering mistakes.
Solder your board. This is a good tutorial if you are new to surface mount soldering.
- Validate that your new board works.
- Explore the aesthetics of the PCB media (e.g. http://ani-liu.com/embedded-aesthetics)
- Tell us who is in your group if you are submitting as a group.
- Submit your Eagle schematic and layout by submitting a .zip file of the design
Submit an image of your schematic and layout. (Example)
- Describe your process and strategy for designing and fabricating your board, including any difficulties you had (1-2 paragraphs)
- Submit a video of the board being used by your pico pro
- Include images of the fabricated PCB. At a minimum show the board before and after assembly.