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VCE Systems Engineering Unit 1 — Electrotechnological systems design

A full semester of Unit 1: students design, produce and evaluate an electrotechnological system that reduces water or energy use. Seven Plug-Run-Play activities — voltage divider, current limiting, light sensing, temperature logging, threshold control, hysteresis and automatic watering — build the skills first, then students run their own design project through the systems engineering process.

Your project brief

Design, produce and evaluate an electrotechnological system that reduces the resources a household, school or community uses — water, energy, or both — by sensing conditions and acting on them automatically.

Your system must sense something real about its environment, decide what to do with that reading, and change an output as a result. It must keep working without someone standing over it.

What "done" looks like

Develop your evaluation criteria from the constraints and considerations in your design brief, and from the parameters of the system itself. A workable set covers both the system and the process:

The system

  1. It is operational — it works, repeatably, without intervention.
  2. It senses a real quantity, and you can show the sensor's readings are trustworthy.
  3. Its output changes in response to the input, at a threshold you can justify.
  4. It addresses the resource problem named in your design brief, and you can quantify the saving.

The process

  1. Your record of evidence shows the decisions you made and why.
  2. Your final system differs from your first design in ways you can explain.

Start here

Weeks 1-2 · Systems, inputs and outputs

Describe any device as input, processing and output, and tell an open-loop system from a closed-loop one.

My lessons

  1. 1

    Weeks 1-2 — Systems, inputs and outputs
  2. 2

    Weeks 2-4 — How electrotechnology got here, and what it costs
  3. 3

    Weeks 4-6 — Components, symbols and circuits

    PRP 1: Voltage divider — calculate, build, measure · PRP 2: Current limiting — why the LED needs a resistor
  4. 4

    Weeks 6-8 — Sensing the world

    PRP 3: Light sensing with an LDR · PRP 4: Temperature and humidity, plotted over time
  5. 5

    Weeks 8-10 — Control, feedback and code

    PRP 5: Threshold control — making a decision · PRP 6: Hysteresis, and open versus closed loop · PRP 7: Automatic watering — sensing, deciding, acting
  6. 6

    Weeks 10-12 — Investigating and defining your own problem
  7. 7

    Weeks 12-13 — Generating and designing
  8. 8

    Weeks 13-14 — Planning and managing
  9. 9

    Weeks 14-17 — Producing and implementing
  10. 10

    Weeks 17-18 — Diagnostic testing and evaluation

My activities

Each Plug-Run-Play activity builds one skill you'll use in your final project.

PRP 1

Voltage divider — calculate, build, measure

Predict a circuit's behaviour with a calculation, then verify it by measurement.
PRP 2

Current limiting — why the LED needs a resistor

Use a datasheet to choose a component value, rather than copying one.
PRP 3 1 sketch

Light sensing with an LDR

Convert a physical quantity into a number, and choose circuit values that make that number useful.
PRP 4 1 sketch

Temperature and humidity, plotted over time

Judge whether a sensor's data is good enough for a control decision.
PRP 5 1 sketch

Threshold control — making a decision

Make a system act on its own reading, and justify the threshold.
PRP 6 1 sketch

Hysteresis, and open versus closed loop

Fix chattering with hysteresis, and choose between open and closed loop deliberately.
PRP 7 1 sketch

Automatic watering — sensing, deciding, acting

Build a complete sense-decide-act system that fails safely.

Glossary

32 terms

Every word you'll meet in this unit. They also pop up inline when you read a lesson.

Actuator
A component that turns an electrical signal into a physical action — a motor, a pump, a solenoid.
Analogue to digital converter (ADC)
The part of a microcontroller that turns a voltage into a number. On these boards, 0-5V becomes 0-1023.
Block diagram
A drawing of a system as labelled boxes and arrows, showing what flows where without showing how any box works inside.
Calibration
Working out what a sensor's raw readings correspond to in real units, by comparing against a trusted reference.
Capacitance
A component's ability to store charge, measured in farads. Capacitors in parallel add (Ct = C1 + C2); in series they combine like parallel resistors (1/Ct = 1/C1 + 1/C2).
Closed-loop control
Control that measures the result of its own action and adjusts. A thermostat.
Current
The rate of flow of charge, measured in amps. Measured by putting the meter in series, in the path the current takes.
Design brief
A statement of the problem, its context, constraints and considerations. It defines what must be achieved without specifying the solution.
Energy
Power multiplied by time. The number behind any claim that a system saves resources, because a saving is only meaningful over a period.
Evaluation criteria
Measurable statements, written before building, used to judge whether the finished system does what the brief required.
Feedback
Information about a system's output being fed back to influence its input. What makes closed-loop control possible.
Forward voltage
The voltage dropped across an LED when it conducts. Different for each colour, and the reason a resistor calculation needs the datasheet.
Hierarchy of control
The ordered set of ways to manage a risk, most effective first. Four steps: 1) eliminate the hazard; 2) reduce the risk, by substituting something less hazardous, isolating people from it, or making an engineering change; 3) administrative controls such as procedures and training; 4) personal protective equipment. PPE is last because it protects one person and only while worn.
Hysteresis
Using two thresholds instead of one, with a gap between them, so an output switches cleanly instead of chattering.
Input
Anything a system senses or receives from its environment.
Milestone
A checkable point in a work plan. If nobody else could confirm it has been reached, it is not a milestone.
Ohm's law
Voltage equals current times resistance (V = I x R). Rearranged, it gives any one of the three from the other two, and it underlies every calculation in this unit.
Open-loop control
Control that acts without measuring the result. A timer.
Output
Anything a system does to its environment as a result of processing.
Parallel circuit
Components connected across the same two points, so each sees the same voltage. Resistors in parallel combine as 1/Rt = 1/R1 + 1/R2, and the total is always less than the smallest one.
Parameter
A measurable property of a system that can be set or optimised — a threshold, a flow rate, a response time.
Power
The rate at which energy is used, measured in watts. P = V x I. A quarter-watt resistor asked to dissipate more than 0.25W will overheat.
Record of evidence
The progressive, multi-modal record of the design process: sketches, photographs, test data, decisions and the reasons for them.
Resistance
Opposition to current flow, measured in ohms. Measure it with the component out of circuit — in circuit, the rest of the board reads in parallel with it and the answer is wrong.
Risk assessment
Identifying what could cause harm in a process, and deciding what to do about it before starting.
Schematic
A circuit drawn with standard symbols, showing electrical connections rather than physical layout.
Sensor
A component that converts a physical quantity into an electrical signal.
Series circuit
Components connected end to end, so the same current flows through each. Resistors in series add: Rt = R1 + R2.
Systems engineering process
The process used throughout this study: investigating and defining, generating and designing, producing and implementing, evaluating, and planning and managing.
Tolerance
How far a component's real value may differ from its marked value. The 1% metal film resistors in this kit, marked 1000Ω, will measure between 990Ω and 1010Ω. Tolerance is usually a smaller source of error than the supply voltage you assumed.
Voltage divider
Two resistances in series across a supply, producing a lower voltage at their junction. The basis of most resistive sensing.
Work plan
The sequence of steps, timeline, milestones, materials, components, tools and processes needed to produce a system.
Maddy, co-founder of Little Bird

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