Electronic environments and embedded systems
This domain assesses a physical system in which a microcontroller reads inputs from sensors and switches, processes them, and drives outputs - and whether you can construct, test and explain it safely.
Core rules and concepts
- Set pin modes deliberately: input, input_pullup, or output. A floating input reads randomly, so use a pull-up or pull-down resistor (or the internal pull-up).
- An LED needs a series resistor: R = (supply voltage − LED forward voltage) ÷ target current. Microcontroller pins supply only small currents (commonly about 20 mA safe, 40 mA absolute maximum), so motors and servos need an external supply plus a transistor or driver board, with a shared ground.
- Analogue sensors such as LDRs, thermistors and potentiometers connect to analogue-to-digital pins; PWM outputs (typically 0–255) dim LEDs and set servo angles.
- Test each subsystem alone - blink an output, print sensor values to the serial monitor - then combine them, recording expected and observed readings.
Worked example
A red LED (forward voltage 2.0 V) on a 5 V supply, target current 15 mA. R = (5 − 2) ÷ 0.015 = 200 Ω, so choose the standard 220 Ω, giving I = 3 ÷ 220 ≈ 13.6 mA - safely inside the pin limit and LED rating. For the light sensor, use hysteresis: switch on below 300 and off above 350, so readings near the threshold do not make the output flicker.
Traps that cost marks
- Omitting the resistor, or powering a motor directly from a pin.
- Forgetting that all supplies must share a ground.
- Showing only final code, with no evidence of subsystem tests or serial-monitor readings.
- No flowchart or pseudocode, and no explanation of what each component does in the system.