This talk is not about circuit design Electrical engineering is a discipline like any other, you learn by experience and mistake. The design process is part intuition, part art and all iterative tenacity. There is no “black magic,” about hardware, just physics and RTFM. Dive in with an Arduino and ‘The Art of Electronics,’ and don’t wuss out while you’re getting up the learning curve.
Hardware is WAY different from software When you are building hardware, you have to physically instantiate your idea. Each instantiation (required to debug problems and test concepts) takes time, money, materials and skills. Compile times are counted in weeks. A working design means you are only 15% done and that the fun part is over. Software project models do not apply.
Hardware Definitions: Intro Hardware is made of PARTS: aka resistors, ICs, switches, batteries and wires combine to make CIRCUITS You buy parts from distributors like Digikey and Mouser Every part has a data sheet For a prototype, you can connect parts by hand ad-hoc and then hack away If it works, stuff happens, you move on If it doesn’t work, you RTFM
Hardware Definitions: CAD
CAD = Computer Aided Design
We don’t make circuit boards by drawing out traces by hand and masking photo resist with tape (why it’s called “tape out”)
Instead, we use 15 year old software suites
EAGLE, Cadence, PCBXpress, Mentor
Hardware Definitions: Libraries + = A “part” or “device” in CAD consists of a “footprint/package” and a “symbol” Your “library” holds all of the devices for your design
Hardware Definitions: using CAD You “design” in a “schematic” The CAD program (eagle, cadence, pcbxpress) extracts a “netlist” from the schematic to create a “layout” You “route” all the IRL copper to connect the devices according to your schematic design.
Hardware Definitions: Fab Once you are done with your “layout,” you extract “gerbers,” aka executable design files A “fabrication house” takes your gerbers and makes a printed circuit board for you An “assembly house” takes your PCBs and your physical parts, your BOM list and assembles your hardware All of these steps can be done by hand, and all the steps are required even with DIY
Prototypes vs. Production
Prototypes vs. Production
Production vs. Prototype
Common mistakesthat will cut you: non-DFM device footprint (YETDA! YETDA! YETDA!) Schematic symbol error (rotated FET syndrome) Non-validated prototype (due to part unavailability or failure to schedule properly) Non-validated components (sourcing from china or last-minute substitutions)
It is possible to be perfect
you don’t need to be an MIT engineer you can make hardware too
Hardware design is back-loaded Do not “begin at the beginning.” Start at the end. Estimate lead times: assembly, fabrication, shipping and BOM cost. Back out cost vs. time and quantity. Select obtainable, known components. Curate your CAD library. Validate your design implementation. Iterate design through prototypes.
Sorry: Abstractions do not exist A good designer considers every layer of “fabrication,” from PCB limitations to the end assembly method in order to make a good design that can be built to specification, on schedule and on budget. Curate as you go. You will be too tired to remember, let alone correct, any of your implementation errors post-facto.
HardwareJargon:Bill of Materials a BOM is the list of all components that are in your design (resistors, ICs, modules, connectors, etc) Reference Designator (R1, U28) Component ID (Digikey/Mouser #) Component Count and Cost Footprint (SOIC-8, TSSOP, 0402) Use/Purpose/Function/Sub-circuit CAD Status
A BOM is just a spreadsheet... a very very very useful spreadsheet
More Jargon:Netlist Connections in schematics are called “nets” A “netlist” is the list of all the nets in your design Use a netlist to validate what you built from what you meant to build (LVS verification) Brandon & I co-wrote the netlist to keep the signal names equal between the board and the code.... in a spreadsheet
Want to make hardware? Start with open-source designs. there’s a full Eagle library, schematic, layout, gerber package and BOM for the ninja boards in my public directory download it, start messing around. http://web.mit.edu/~awozniak/www/ninjas/
but now we’re out of time START BUILDING STUFF & ASK QUESTIONS
until next time... Here ARE SOME RESOURCES for hardware beginners that ladyada Put together just for you http://www.adafruit.com/ tutorials