System Design
Putting it all together: designing a project that works, keeps working, and can be fixed.
The question
How do engineers design a device that has to work outdoors through a prairie winter, unattended, for months?
What you’ll discover: how to turn an idea into a working, reliable system: requirements, power budgets, reliability, enclosures, data integrity, testing and maintenance.
In simple terms
BeginnerStart with what it must do
Engineers start with requirements: clear statements of what the system must do, before choosing any parts. For a weather station, they might be:
- Measure outdoor air temperature to within about 0.5 °C (0.9°F), every 5 minutes.
- Keep working from −40 °C (−40°F) to +40 °C (104°F), in rain, snow and wind. (A Pico is rated only down to −20 °C (−4°F), which is why the electronics stay indoors and only the probe goes outside.)
- Store at least a month of readings, and never invent a reading it didn’t take.
- Be easy to check, clean and repair.
Every later choice is checked against these.
The design checklist
- Power budget: how much energy it uses, and how it will get it (Lessons 27 and 28).
- Reliability: what could fail, and what happens if it does?
- Enclosure: protection from water, dust, sun, cold and curious animals.
- Data integrity: readings that are checked, timestamped and stored safely.
- Testing: on the bench first, then in real conditions.
- Maintainability: labels, documentation and parts you can replace.
Go deeper
IntermediateReliability and enclosures
Watchdog timers: a program can freeze from a rare bug or electrical glitch. A watchdog is a hardware timer that resets the microcontroller unless the program “feeds” it regularly, so a frozen system restarts itself. The Pico has one (machine.WDT).
Enclosures: look for an IP rating, such as IP65 (dust-tight and protected against water jets). Condensation forms inside sealed boxes when the temperature drops, so a small vent with a membrane, or a bag of silica gel, helps. Sunlight heats dark boxes and breaks down some plastics. Cold slows LCD displays and weakens batteries. And a temperature sensor must sit outside the electronics box, in a shaded, ventilated radiation shield (Lesson 29), because the box itself warms up in sun.
AdvancedData integrity, testing and maintenance
Data integrity means stored data can be trusted: each reading is checked against sensible limits, failed readings are recorded as gaps rather than guesses, timestamps are clear, and files are written so a power cut loses at most one reading.
Testing happens in stages: each part on the bench, then the whole system on the bench for several days (a burn-in), then outdoors alongside a trusted reference. Write down what you tested and what happened, including failures.
Maintainability means someone, possibly you in a year, can understand and fix it: a labelled wiring diagram, commented code, a parts list, and a maintenance log for cleaning the rain gauge, checking the radiation shield and replacing batteries.
Quick check
What are requirements?
Clear statements of what a system must do, written before choosing parts.
What does a watchdog timer do?
It resets the microcontroller if the program stops feeding it, so a frozen system restarts.
Why must an outdoor temperature sensor be outside the electronics box?
The box warms in the sun, so a sensor inside would read too warm.
Words to know
- Requirement
- A clear statement of what a system must do.
- Watchdog timer
- A timer that resets a frozen microcontroller.
- IP rating
- A code for how well an enclosure keeps out dust and water.
- Burn-in
- Running a system for an extended period to catch early failures.
Learn more
- Environment and Climate Change Canada: measuring temperature: how official climate stations place thermometers
- Capstone: My Weather Station
Electronics School is part of the Discovery Zone. Every activity here runs on small batteries or a USB cable: never wall outlets. The one plug-in tool is the optional soldering iron, set up by an adult.