Topic 3.4: Electronic systems Questions

A thermostat circuit contains a thermistor and a variable resistor in series across a 9 V supply, with the junction connected to a transistor base, and a relay coil with a diode across it in the transistor's collector circuit. Explain what this circuit does.

Which behaviour is essentially free in program control but expensive in analogue?

A hospital infusion pump must alert staff when a line is blocked. Justify the output devices you would specify.

A washing machine weighs its load and uses less water for a small one. Which benefit is this?

A connected kitchen scale weighs to the nearest gram and sends the reading to a phone. Describe the role of the op-amp in it.

An automatic hand dryer switches on when hands are placed beneath it. Describe it as an electronic system, including its feedback.

A school replaces its analogue intercom with a digital one running over its computer network. Analyse the two systems against each other.

Why is a resistive sensor placed in a voltage divider?

A domestic smoke alarm uses analogue signal conditioning for its sensing and a microcontroller only for its test button, low-battery chirp and hush function. Justify this division.

A washing machine's controls are built around a single microcontroller. Explain why, and what it replaced.

Why does a practical op-amp amplifier have feedback resistors?

A city fits embedded systems to its public bins so they report when they are full. Explain what this adds, and what it risks.

Which stage of analogue signal conditioning turns a varying signal into a decision?

What is the main reason a designer chooses a microcontroller over discrete components?

A manufacturer replaces the mechanical timer in a washing machine with an electronic control board and a phone app. Evaluate this decision.

A bathroom extractor fan is to run automatically when someone showers. Explain a suitable input device and how its signal is made usable.

Which of these is found inside a microcontroller?

An indicator LED on a kettle needs 20 mA at 2 V and is connected to a 9 V supply through a series resistor. Apply the equations to specify that resistor.

A workshop guillotine may only operate when its guard is down and both of the operator's hands are on separate buttons. Explain the logic and why it is hard-wired rather than programmed.

A microcontroller switches a 230 V immersion heater through a transistor and a relay, with a diode across the relay coil. Explain the purpose of each of those three components.