Microcontroller Applications and System Evaluation
Microcontrollers Everywhere
In the previous lesson you learned how a microcontroller is programmed using a flowchart. In this lesson you will see where microcontrollers are actually deployed — from the engine bay of a modern car to the drum cycle of a domestic washing machine — and develop the skill of evaluating and improving an existing flowchart program against a design specification.
Modern vehicles and household appliances rely on dozens or even hundreds of microcontrollers working together. Understanding why engineers choose a programmable device over a hardwired circuit, and being able to spot where a given flowchart falls short of its specification, are both directly examinable skills.
Vehicle Applications
Modern cars contain multiple microcontroller-based control units. Four useful examples are:
An engine management system continuously monitors sensors for engine temperature, air mass flow, throttle position, oxygen content in the exhaust and crankshaft speed. The microcontroller processes these readings thousands of times per second and adjusts fuel injection timing, ignition advance and idle speed to maintain efficient combustion. Without a programmable device, matching all these variables simultaneously would require an impractically complex analogue circuit. The microcontroller can also store fault codes when a sensor reading goes out of range, allowing a technician to diagnose faults quickly.
Anti-lock braking (ABS) — wheel-speed sensors feed data to a microcontroller. If one wheel decelerates much faster than the others (the signature of a locked wheel), the microcontroller rapidly pulses the brake hydraulics at that wheel to restore rotation. This happens around 15 times per second, far faster than a human can pump the pedal.
Airbag deployment — accelerometers detect a sudden large deceleration that matches the pattern of a collision. The microcontroller must distinguish a crash from a pothole in milliseconds. If the deceleration exceeds the programmed threshold, it fires the airbag inflator. Speed is critical: the entire sequence from impact to full inflation takes around 30 milliseconds.
Climate control — temperature and humidity sensors feed a microcontroller that adjusts fan speed, heating element power and air distribution flaps to maintain the cabin at a set temperature. The microcontroller runs a continuous control loop, comparing the measured temperature to the target and correcting any difference.
Domestic Appliance Applications
The same technology that manages a car engine also controls everyday household devices:
- Washing machine — a microcontroller sequences the wash cycle: filling the drum to a set water level (detected by a pressure sensor), heating the water to the correct temperature, rotating the drum at different speeds for wash and spin, and draining at the end. Different programs (cottons, delicates, quick wash) are simply different stored sequences — no hardware change needed.
- Dishwasher — similar cycle control: water fill, heat, spray pump, drain and rinse, with a heated drying phase. Temperature sensors prevent over-heating; a turbidity sensor in some models detects how dirty the water is and adjusts the cycle length accordingly.
- Central heating system — a thermostat microcontroller compares the room temperature from a sensor to the set-point temperature. If the room is too cold, it opens a valve and starts the boiler; when the set temperature is reached, it closes the valve. A time clock sub-program runs a heating schedule so the house is warm at the right times of day.
Vehicle applications: engine management, ABS braking, airbag deployment, climate control. Domestic applications: washing machine, dishwasher, central heating. In every case the microcontroller reads sensor inputs, processes them against a stored program, and drives output devices — replacing the equivalent analogue or discrete-logic circuit.
Why Microcontrollers Replaced Discrete Circuits
Four common reasons engineers choose microcontrollers are:
- Flexibility and reprogrammability — changing the system’s behaviour requires only a software update, not a new circuit board. A car manufacturer can issue a “recall” software fix or add a feature to next year’s model without redesigning hardware.
- Lower cost at scale — a single microcontroller chip costs far less than an equivalent collection of discrete logic ICs, timers and counters. When millions of washing machines are produced each year, the savings are significant.
- Smaller physical footprint — one chip replaces a circuit board full of components, reducing size and weight. In a car, this matters for packaging; in a domestic appliance, it allows more compact designs.
- Ability to integrate sensors — many microcontrollers include built-in analogue-to-digital converters, timers, and communication interfaces on the same chip, reducing the number of external components further.
Four reasons microcontrollers replaced discrete circuits: reprogrammability (change software, not hardware), cost at scale (one chip cheaper than many ICs), smaller footprint (one chip replaces a board of components), and integrated peripherals (ADC, timers, comms on chip).
Evaluating a Flowchart Program
Exam questions regularly give you a partially correct flowchart and ask you to: (a) identify what it does correctly, (b) spot where it does not meet the specification, and (c) describe or draw the modification needed. This is the flowchart evaluation technique. Use this three-step method:
- Trace through the flowchart — follow the arrows step by step. Write down what the program actually does for a given set of input conditions. Be systematic: go through each branch of every decision diamond.
- Compare to the specification — read the written specification line by line and check whether the flowchart implements each requirement. Common omissions: a missing decision diamond (condition never tested), a missing output block (action never taken), a loop arrow pointing to the wrong step, or a counter that is never reset.
- Describe the modification — state precisely which block type to add or change and where to insert it in the flow. “Add a decision diamond after the delay block asking ‘Is count = 5?’ with YES leading to reset and NO looping back to the increment block” is a complete answer. “Add a counter somewhere” is not.
Specification: The boiler should turn on when the room temperature falls below 18 °C. It should turn off when the temperature reaches 21 °C. The system should repeat this cycle continuously.
Flowchart provided (with a fault):
- START → Read temperature sensor → Is temperature < 18 °C? YES: Turn boiler ON → loop back to “Read temperature sensor”. NO: Turn boiler OFF → loop back to “Read temperature sensor”.
Fault identified: The flowchart turns the boiler OFF whenever temperature is 18 °C or above, including at 19 °C and 20 °C. This means the boiler switches off before the room reaches 21 °C, wasting energy. The specification requires the boiler to run until 21 °C is reached.
Modification: When the YES branch turns the boiler ON, add a new decision diamond: “Is temperature ≥ 21 °C?”. The NO exit loops back to “Read temperature sensor” (keeping the boiler on). The YES exit leads to “Turn boiler OFF” and then loops back to the first decision. This creates two separate thresholds, matching the specification.