Programmable Components and Microcontrollers
Why Use Programmable Components?
Traditional electronic circuits are designed to do one thing. Change the task and you change the circuit — which means redesigning the hardware and going back to manufacture. Programmable components solve this problem. They allow engineers to change what a circuit does simply by loading a different program, with no change to the physical components. This makes products cheaper to develop, easier to update and more versatile — a significant commercial advantage for any manufacturer.
Microcontrollers and PICs
The most important type of programmable component in GCSE Design and Technology is the microcontroller. A microcontroller contains:
- A processor (CPU) — executes the instructions in the program, performing calculations and making decisions.
- Memory — stores the program (in non-volatile flash memory, so it survives power loss) and temporary working data (in RAM).
- Input/output (I/O) pins — connect to sensors, switches, LEDs, motors and other peripheral devices. Pins can be individually configured as inputs or outputs.
A PIC (Programmable Interface Controller) is a popular family of microcontroller chip. PICs are small, low-cost and low-power, making them ideal for embedding in consumer products such as washing machines, microwave ovens and children’s toys. A PIC is programmed by writing code on a computer and then uploading it to the chip via a programmer device.
A microcontroller contains a processor, memory and I/O pins on a single chip. It can read sensor inputs, make decisions according to its program, and control output devices — replacing a large number of separate electronic components with a single programmable unit.
Interfacing with Inputs and Outputs
A microcontroller sits at the process stage of the input–process–output model. It interfaces with input sensors and output devices via its I/O pins:
- Input interfacing — a sensor (LDR, thermistor, microswitch) connects to an input pin. The microcontroller reads the voltage at that pin and compares it to a threshold in its program. For analogue sensors, an internal analogue-to-digital converter (ADC) converts the continuously varying voltage to a number the processor can use.
- Output interfacing — output pins switch devices on or off. Because a microcontroller’s output pins can only supply small currents (typically 20–40 mA), high-power devices such as motors must be controlled via a transistor or relay, which acts as a switch that the microcontroller triggers.
Programs running on microcontrollers are made more efficient using sub-routines. Instead of writing the same sequence of instructions every time a task is needed, the programmer writes the instructions once as a sub-routine and calls it whenever required. For example, a “sound alarm” sub-routine that pulses a buzzer three times could be called from many different points in the program — when temperature exceeds a limit, when a door opens, or when a battery runs low — without rewriting the buzzer code each time.
A macro is a shorthand label assigned to a frequently used sequence of instructions. In block-based or flow-chart programming environments (common in schools), macros allow students to group a set of actions under one name and use it as a single step. Both sub-routines and macros reduce the length and complexity of programs, making them easier to test, debug and modify.
Benefits of Reprogrammable Systems
The ability to reprogram a microcontroller after the product is assembled brings several practical advantages. Explain each one with a product context:
- Flexibility — the same hardware can be used in different products simply by changing the program. A manufacturer can produce one PCB design and program it differently for a bedroom alarm clock and a kitchen timer.
- Firmware updates — faults discovered after a product ships can be corrected by updating the program over a network or via a USB connection, without recalling and physically modifying the hardware.
- Reduced component count — one microcontroller replaces many discrete components (comparators, counters, timers), reducing board size, material cost and assembly time.
- Faster prototyping — engineers can write, test and refine the control logic rapidly without soldering new components. This shortens the development cycle and reduces waste.
Programmable systems can be updated after manufacture by changing the software, with no change to the physical circuit. This is a major commercial advantage: it reduces tooling costs, enables bug fixes without product recalls, and allows one hardware design to serve multiple product variants.
Limitations of Programmable Components
Microcontrollers are not always the best choice. Students must be able to evaluate both sides:
- Programming expertise required — writing reliable control software demands skill. Bugs in the code can cause dangerous malfunctions in safety-critical products.
- Higher unit cost for simple tasks — for a product that only ever needs to do one thing (such as a simple on/off switch), a fixed resistor-transistor circuit is cheaper and more reliable than a microcontroller.
- Power consumption — a microcontroller consumes more power than a simple passive circuit, which matters in battery-powered products where runtime is critical.
- Software dependency — if the program is corrupted (e.g. by a power surge during programming), the product fails entirely. A purely hardware circuit has no software to corrupt.
Microcontrollers are embedded in a huge range of everyday products. A modern washing machine uses a microcontroller to time wash cycles, monitor water temperature via a thermistor, detect an unbalanced drum via an accelerometer, and control the motor speed — all in a single chip. Without reprogrammability, manufacturers would need to produce different circuit boards for each wash programme (delicates, cottons, quick wash) instead of a single board with different software settings.
In Design and Technology projects, PICs are commonly programmed using block-based visual environments such as Flowcode or PicAxe BASIC. These tools generate machine code from a visual flowchart or simple text commands, making programming accessible without requiring advanced software engineering skills. The logic the student builds in the flowchart maps directly onto the sub-routine structure described in this lesson.