Electronic Systems & Programmable Components
Electronic Systems & Programmable Components
Many everyday products only work because of an electronic system hidden inside them — a security light that switches on in the dark, a washing machine that responds when the drum is full, or a toy that beeps when a button is pressed. Sections 1.6 and 1.7 of the specification group these components into three jobs: sensing what is happening, controlling what happens next, and producing an output. This lesson also covers how programmable components use flowcharts to embed that behaviour into a real product, so the same hardware can be made to behave in different ways just by changing its program.
Sensors: The Inputs of a System
A sensor is the input of an electronic system. It detects a change in the environment and turns it into an electrical signal that the rest of the circuit can use to make a decision. Two sensors named in the specification are the light-dependent resistor and the thermistor, and both work by changing their resistance in response to the environment around them.
A light-dependent resistor (LDR) changes its resistance depending on how much light falls on it — in bright light its resistance is low, and in darkness its resistance is high. This makes it useful in automatic security lights and streetlights that need to know when it has become dark enough to switch on. A thermistor behaves in a similar way but responds to heat instead of light, so its resistance falls as the surrounding temperature rises. Thermistors are used in thermostats and cooking appliances to monitor and control temperature.
An LDR's resistance decreases as light increases; a thermistor's resistance decreases as temperature rises. Both convert an environmental change into a usable electrical signal.
Control Devices: Switches, Transistors and Resistors
Between the sensor and the output sits the control stage. The simplest control device is a switch, which opens or closes a circuit manually or automatically. A transistor does a similar job electronically: a small current or voltage at one connection switches a much larger current on or off. This is why transistors are used to let a weak signal from a sensor control a more powerful output, such as a motor or a bright lamp, that the sensor alone could never drive directly. A resistor limits the current flowing through part of a circuit, which protects delicate components such as LEDs from being damaged by too much current passing through them.
In a torch-style circuit, a transistor lets a small push switch (which only carries a low current) trigger the transistor to switch on a bulb that needs a much bigger current than the switch itself could safely carry. A resistor placed in series with an LED stops too much current reaching it, which would otherwise burn the LED out almost instantly. Choosing the correct resistor value is a common calculation-style question, because too little resistance damages the component while too much resistance makes the output too dim or weak to work properly.
Outputs: Buzzers and LEDs
The output stage performs the action the system was designed to produce. A buzzer converts an electrical signal into a simple sound, commonly used in alarms, timers and reminders where a clear, low-cost alert is needed rather than complex audio. A light-emitting diode (LED) converts an electrical signal into light and only allows current to flow through it in one direction. LEDs are widely used for indicator lights, digital displays and low-energy illumination because they use far less power than a filament bulb and last for a much longer time before failing.
Buzzers convert a signal into sound and are used in alarms; LEDs convert a signal into light and only allow current to flow in one direction.
Flowcharts and Programmable Components
Many modern products use a programmable component — a small chip that can be written with instructions to control outputs based on the data it receives from its inputs. Before writing this program, designers plan it using a flowchart. A flowchart shows the order of steps a system follows, including exactly where it checks a sensor reading and makes a decision about what to do next, so the logic can be checked before any code is written.
A flowchart for an automatic nightlight would start with an input step that reads the LDR. Next comes a decision step asking “is it dark?” If the answer is yes, the flowchart moves to an output step that switches the LED on; if the answer is no, it loops back and checks the LDR again a moment later. This shows how a flowchart plans a decision before any code is written, so a third party could follow the logic of the program without ever seeing the code itself.
The decision step above is the key idea in this part of the specification: a programmable component switches an output on or off depending on the input data it receives and the decision built into the program, rather than simply being wired directly to a switch. This means the same hardware can behave in completely different ways just by changing the program — for example, changing the exact light level at which the nightlight decision is triggered.
Some inputs, such as an LDR or thermistor, do not just give a simple on/off signal. They give an analogue input — a value that changes gradually across a range, such as a light level moving smoothly from bright to dark. A programmable component must process this changing value, not just detect that it has switched between two fixed states, so that it can respond proportionally, for example dimming a light gradually rather than snapping it fully on or off.
Programs also use simple routines to control the timing and repetition of outputs. A delay pauses the program for a set amount of time, for example keeping a light switched on for thirty seconds after it is first triggered. A loop repeats a sequence of steps, such as continually checking a sensor while the system waits for a change to happen. A count keeps track of how many times something has happened, for example counting the number of times a button has been pressed before triggering an output.
A delay pauses a program for a set time, a loop repeats a set of steps, and a count tracks how many times an event has occurred.