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Hardware Design Considerations
Designing smart, secure, and power efficient devices is truly an art. The design process from concept to deployment can be long and arduous but at the end of the day, it is truly rewarding to see your creation come to life.
In our earlier blog, we had taken a look at why hardware design is hard. Some of the points we raised were:
Challenge #1 - No “undo” button.
Challenge #2 - Long development cycle
Challenge #3 - Keeping up to date.
Challenge #4 - Added complexity.
Challenge #5 - Hitting cost requirements.
Challenge #6 - “Can’t you build it for $10?”
Challenge #7 - Overseas production
Challenge #8 - Shrinking components
A successful hardware design is when the device successfully meets required functionality, can be easily manufactured, is reliable and withstands the environment it was designed for. With this in mind, I plan to bring you some suggestions on Do’s and Don’ts of Electronic Hardware Design as a two-part series. These principles are a quick and easy guideline to design engineers looking at being efficient and saving time and money (not to mention headaches) right from the start.
This first series of the blog focuses on the list of Do’s, the design considerations to keep in mind when designing embedded electronic hardware systems.
The Do’s: Considerations in Hardware Design
1) Do know your components.
Read the entire data sheet and all reference materials thoroughly to ensure understanding of the part capabilities and limitations.
2) Do understand the operating environment
a. The system must be designed to tolerate the environmental requirements and conditions. For example, a system that operates solely indoors will have very different requirements than a system that operates outdoors in all weather conditions.
b. The operating temperature range, pressure, humidity, required ruggedness, exposure to radiation, etc. must all be considered in the design and validation phases.
c. Don’t forget about power dissipation and thermal analysis
b. The operating temperature range, pressure, humidity, required ruggedness, exposure to radiation, etc. must all be considered in the design and validation phases.
c. Don’t forget about power dissipation and thermal analysis
3) Do design in additional margin where possible
Don’t hem yourself in where you don’t have to. Adding provisions for additional capacitance, the ability to increase current limits, supporting higher-resolution screens, etc. are all good ideas as long as other constraints (e.g., cost) don’t override them. Keeping options open gives you more flexibility down the road. This is also applicable for power supplies – over-design them when possible to allow for future functionality and increased power draw.
4) Do plan for future features where possible.
If you know a feature, or an upgrade may be coming, plan for it early on whenever practical. Again, this leaves you with more options in the long run.
Design for flexibility. As a typical hardware project turn around time is at least 4 to 6 weeks, plan ahead to incorporate some “additional” options that may prevent the need for an additional spin to add a feature down the road. This for example can include adding a footprint for a Wi-Fi and Bluetooth module, but not populating it unless/until needed.
5) Do add provisions to ease debugging.
Make debugging easier on yourself and your team during the board bring-up and development phases. You will be thankful later.
a. One good way to start: use pull-up/down resistors instead of making direct connections to VDD and GND for IC configuration pins.
b. Give yourself options to disconnect power supply inputs and outputs in case you need to take current measurements or otherwise isolate supply rails.
c. Make the firmware developer’s life easy. Consult them early in the design for what interfaces may help them develop and test the code. This usually includes a debug port (SWD, JTAG, etc.), a UART, and one or more GPIOs or LEDs.
d. Always think testing - add ample test points for automated production testing in a “bed-of-nails” or similar type test jig. A product can only be successful if it can be manufactured and tested reliably. Untested or poorly tested designs can hurt customer relations and the bottom line greatly with extensive returns and RMAs.
b. Give yourself options to disconnect power supply inputs and outputs in case you need to take current measurements or otherwise isolate supply rails.
c. Make the firmware developer’s life easy. Consult them early in the design for what interfaces may help them develop and test the code. This usually includes a debug port (SWD, JTAG, etc.), a UART, and one or more GPIOs or LEDs.
d. Always think testing - add ample test points for automated production testing in a “bed-of-nails” or similar type test jig. A product can only be successful if it can be manufactured and tested reliably. Untested or poorly tested designs can hurt customer relations and the bottom line greatly with extensive returns and RMAs.
6) Do add electrostatic discharge (ESD) and other protections.
ESD is inevitable on any user-accessible interface, so plan accordingly to protect your design. Use protection diodes, current-limiting resistors, and other devices to protect every pin exposed to the outside world.
7) Do add electromagnetic interference (EMI) mitigations.
EMI problems can be far-reaching and negatively impact your device’s performance, reliability, and ability to be sold to the public. Regulatory restrictions vary around the world but in general most electronic products will need to comply with one or more sets of EMI restrictions. Minimize your chances for EMI issues from the start of the design, by adding common-mode chokes, ferrites, and other EMI-suppressing devices to all connector interfaces. Prefer balanced, differential interfaces over single-ended for high-speed signals whenever practical.
8) Do consider the BOM cost early on.
If the BOM costs get carried away, the project may be doomed from the start. Careful planning and estimating with your designers can help avoid unwelcome surprises. Keep an eye on the BOM cost throughout the design phase.
9) Do consider component availability.
Work with your preferred distributor(s) early on to understand availability and lead times for your critical components. Passives like resistors and capacitors can generally be replaced with form/fit/function (FFF) compatible alternatives during manufacturing, but this may not be possible for other components like ICs and connectors.
10) Do produce clean, well-documented schematics.
Nothing is worse than having to look at a cluttered rat’s nest of a schematic diagram and try to make sense of it.
a. Build organized, easy-to-read schematics. A good idea is to use a hierarchical topology, place inputs on the left of sub sheets and outputs on the right.
b. Add notes through the schematics to indicate design considerations, IC settings, filter parameters, and other non-trivial information to whoever looks at the schematic next.
c. Specify all component parameters for the BOM. Be leery of specifying “generic” for anything but resistors. Even capacitors with the same capacitance, voltage, dielectric, and package types can vary a lot from manufacturer to manufacturer.
b. Add notes through the schematics to indicate design considerations, IC settings, filter parameters, and other non-trivial information to whoever looks at the schematic next.
c. Specify all component parameters for the BOM. Be leery of specifying “generic” for anything but resistors. Even capacitors with the same capacitance, voltage, dielectric, and package types can vary a lot from manufacturer to manufacturer.
These are some of the points I would suggest focussing on and following while designing successful electronic hardware systems. At NeuronicWorks, we have fostered a culture of following these principles when building modern, resilient, optimized, and efficient hardware designs.
My next blog will look at some of the Don’ts – points to keep in mind and avoid while designing resilient, smart, and power efficient hardware devices. Stay tuned.
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