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Section 1: Electronic Control Systems

Almost every modern device — from a microwave oven to a car engine — uses an electronic control system. These systems allow devices to respond to the world around them, make decisions, and control outputs automatically.

Any electronic control system can be broken down into three parts:

Devices that combine electronic control with moving mechanisms are called mechatronic systems. A washing machine, robot arm or delivery drone are all mechatronic — electronics tells the mechanisms what to do.

Inputs and outputs

In general, all systems need inputs from the outside world to sense what is happening and need outputs to influence it.

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Section 2: What is a Microcontroller?

A microcontroller is often described as a computer-on-a-chip. It contains a processor, memory and input/output connections all in a single small, inexpensive package. Because of this, microcontrollers can easily be built into everyday products to make them more intelligent.

It is easy to think of a microcontroller only as a diagram or a symbol, but it is a real physical device — and different manufacturers package one very differently. The photograph below shows two boards commonly used in schools. On the left is an Arduino Uno: the main chip sits at the centre of the board, surrounded by the digital and analogue input/output pins along the edges, with a USB connector for programming and a power socket. On the right is a PICAXE project board, along with a bare PICAXE chip of the kind you'll find plugged into it — PICAXE chips are programmed in a similar way to an Arduino, but are typically mounted onto a simpler board that adds just the input/output connections and a power supply needed for a specific project.

Unlike a general-purpose computer, a microcontroller is typically programmed to do one specific job. The key advantage is flexibility — the same hardware can be reprogrammed to do something completely different simply by changing the software.

Away from the physical hardware, a microcontroller is drawn differently again depending on which software or exam paper you are looking at. The image below shows three examples: in Yenka, it appears as a simple green block with numbered inputs and outputs; in NoSyntaxSim, it appears as an on-screen component with input and output devices connected directly to it; and in a QS examination or assignment, it is drawn even more simply, as a plain rectangle with numbered pins down each side. All three are showing the same idea — inputs on one side, outputs on the other — just presented in the style of whichever tool you're using.

Hard-wired circuits

It is possible to produce electronic control circuits without microcontrollers, but they usually need a lot more parts and are significantly more complex. A control circuit without a programmable element is called a hard-wired circuit.

Advantages of microcontrollers

• Reliability — fewer separate components means fewer things to go wrong
• Compact — one chip replaces many separate components, saving space
• Flexible — reprogramming changes what the product does without changing hardware
• Rapid development — changes to the product are made in software, not by redesigning the circuit
• Low cost — mass production makes microcontrollers very inexpensive

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Section 3: Flowcharts

A flowchart is a graphical way of planning and communicating a control sequence. It shows exactly what the microcontroller should do, in what order, and under what conditions. Flowcharts are used in the QS assignment and exam — you must be able to read, draw, correct and simulate them.

Standard QS flowchart symbols

A flowchart determines the order in which instructions are followed by the microcontroller — it is the plan the program must execute, step by step. Each type of instruction (starting/stopping, inputting/outputting, processing, or deciding) has its own standard box shape, so that anyone reading the flowchart can immediately recognise what kind of instruction each box represents, without needing to read every word.

These symbols are taken from the QS data booklet.

(although the sub procedure symbol is not assessed at National 5 level)

A flowchart could simply be a single run of commands from start to finish, ending once the last instruction has been carried out. The example below starts the program, turns an output ON, waits for a set time, then turns the output OFF before stopping.

However, a flowchart like this would only run through once before stopping. In practice, it is far more common for microcontroller programs to run continuously — repeating the same sequence over and over. This is called a continuous loop. The example below shows this using the flow line symbol, which loops back to an earlier point in the sequence instead of reaching STOP, so the sequence repeats indefinitely.

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Section 4: Drawing Flowcharts from a Specification

In the QS exam and assignment you will be given a written specification and asked to draw a flowchart. Read the specification carefully — each step becomes one or more boxes in the flowchart.

What is a pin?

A microcontroller connects to the outside world through a number of pins along its edges — each one is a physical connection point that can be wired to an input device (like a switch) or an output device (like an LED). Every pin has its own number, such as D8 or D2, so that a flowchart or program can refer to exactly the right connection. From here on, worked examples and questions will refer to specific pin numbers — always check the pin table given with a task to see which device is connected to which pin.

Method

1. Read the full specification first
2. Identify all inputs and outputs from the pin table
3. Draw a START terminal
4. Work through the specification step by step — one action per box
5. Use Decision boxes for any "wait until…" or "if… then…" conditions
6. Use Process boxes for all delays (with units)
7. Use In/Out parallelograms to turn outputs ON or OFF
8. Add a continuous loop arrow back to the start if the sequence repeats

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Section 5: Using Inputs — Decision Boxes

Most real control systems respond to sensor inputs. A decision box (diamond) checks whether an input is ON or OFF and branches the flowchart accordingly.

Waiting for an input

To make the program wait until a button is pressed, use a decision box that loops back to itself on the NO branch:

This is called a polling loop — the microcontroller keeps checking the input until it becomes active.

AND control — both inputs must be active

When two conditions must both be true before continuing, two decision boxes are placed in series. The YES output of the first leads into the second decision. Only when both return YES does the program continue — and if the second condition is not met, the flowchart loops all the way back to the first decision, not just the second. This matters: without looping back to the top, the two inputs could be triggered one after another (rather than together) and the program would still be allowed through.

OR control — either input can be active

When either of two conditions being true is enough to continue, two decision boxes are placed in parallel. The YES output of either one leads to the same next step.

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Section 6: Finite (Counted) Loops

A finite loop — also called a fixed loop, a counted loop, or a for loop — repeats a sequence a set, predetermined number of times decided in advance, then stops and moves on. This is different from a continuous loop, which has no predetermined end and repeats indefinitely.

To create a for…next loop in a flowchart, a variable (e.g. count) is used to keep track of how many times the loop has run:

1. Initialise the variable: count = 0
2. Perform the repeated action (e.g. flash an LED)
3. Increment the variable: count = count + 1
4. Decide: is count < target number? YES → repeat. NO → exit loop.

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Section 7: Reading and Correcting Flowcharts

In the QS exam you will often be given a flowchart that contains errors and asked to identify and correct them. Common errors include:

• Missing delay units (writing "500" instead of "500 ms")
• Wrong pin number used in an input or output box
• Decision box branching the wrong way (YES and NO swapped)
• Missing connection — the loop does not return to the correct point
• Wrong order of steps (e.g. turning a device ON after the delay instead of before)
• No START or STOP terminal
• Wrong flowchart symbol used (e.g. a rectangle instead of a diamond for a decision)

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Section 8: Inputs, Outputs and Pin Numbers

The microcontroller used in NoSyntaxSim is based on the Arduino platform. Inputs and outputs connect to numbered digital pins (D2–D13). In the QS exam, you will always be given a pin table telling you which pin connects to which input or output device.

If you are using a PICAXE chip instead, pins are numbered slightly differently — as b.0 to b.7 rather than D2–D13. QS flowchart questions and answers only ever use plain pin numbers (like D8), regardless of which hardware a class happens to be using, so that's the numbering to use when answering questions.

Example pin table

Pin	Direction	Device
D2	INPUT	Push button (start switch)
D3	INPUT	Temperature sensor
D4	INPUT	Pressure pad
D5	INPUT	Reset button
D8	OUTPUT	Red LED
D9	OUTPUT	Green LED
D10	OUTPUT	Motor
D11	OUTPUT	Buzzer

Digital inputs

A digital input can only be logic 1 (ON) or logic 0 (OFF). A push button is digital — it is either pressed or not. In a decision box in a flowchart, a digital input is checked as: "Is D2 ON?"

Some inputs — like a thermistor or an LDR — can physically vary smoothly rather than switching cleanly between two states. At this level, you can still treat them as behaving digitally: they are simply LOW until a particular point is reached (e.g. a temperature or light level), then they become HIGH. In Yenka and in some tasks, this is exactly how these inputs are controlled and checked in a flowchart.

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Section 9: Generating Code

One of the most powerful features of NoSyntaxSim is that it can automatically convert your flowchart into real code — either Arduino C++ or pBASIC (the language used by PICAXE chips), depending on which target you choose. This is the actual code that would run on a physical microcontroller.

While you do not need to write or memorise code for the N5 exam, you may be asked to read a short piece of code and correct an error in it, so understanding the connection between a flowchart and the code it produces is useful preparation.

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Output Drivers

A microcontroller pin can only supply a small current — not enough to directly drive a motor or solenoid. An output driver (typically a transistor or relay) amplifies the signal to power the output device. In exam circuits, a transistor driver circuit is commonly shown between the microcontroller output pin and the output device.

This circuit uses three outputs. Output5 (LED) and Output6 (buzzer) both draw very little current, so they run directly from the microcontroller's own supply. Output7 drives a transistor, which switches a relay coil — the relay's separate contacts then control a motor circuit running from a much higher voltage (24 V), since that's more current and voltage than the microcontroller or transistor could handle directly. The diode across the coil protects the transistor from the voltage spike produced when the relay switches off.

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Section 10: Design Challenges

For each challenge below, follow the full engineering process: read the specification carefully, design a flowchart, then build and simulate it in NoSyntaxSim. Test it against every point in the specification, and once it's working, export your solution and paste it into your notes as a record of your finished system.

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Challenge 1 — Fire alarm for a Cairngorms village hall

A village hall in the Cairngorms is having a control system fitted ahead of the winter ceilidh season, so the caretaker can arm the fire alarm overnight without needing a full commercial installation.

Pin	Direction	Device
D2	INPUT	Master arm switch
D3	INPUT	Heat sensor
D4	INPUT	Manual alarm button
D5	INPUT	Reset switch
D8	OUTPUT	Alarm

i	The master switch (D2) must be pressed to arm the system.
ii	Once armed, if the heat sensor (D3) is activated OR the manual alarm button (D4) is pressed, the alarm (D8) sounds.
iii	The alarm continues to sound until the reset switch (D5) is pressed.
iv	After reset, the system returns to waiting in the armed state.

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Challenge 2 — Starting signal for the Braemar hill races

The organisers of a Highland Games hill race want an automated starting signal, similar to the red-amber-green sequence used to start races at professional athletics meetings, so a single steward can start each wave of runners consistently.

Pin	Direction	Device
D2	INPUT	Start button
D8	OUTPUT	Red LED
D9	OUTPUT	Amber LED
D10	OUTPUT	Green LED
D11	OUTPUT	Buzzer

i	Wait until the start button (D2) is pressed.
ii	Red LED (D8) ON — wait 3 s.
iii	Red (D8) OFF, Amber (D9) ON — wait 1 s.
iv	Amber (D9) OFF, Green (D10) ON, Buzzer (D11) ON — wait 0.5 s.
v	Buzzer (D11) OFF — Green LED stays ON.
vi	The system waits for the next race (continuous loop back to step i).

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Challenge 3 — Visitor counter for V&A Dundee

V&A Dundee wants a simple visitor counter fitted at a gallery entrance, so staff can see at a glance how many people are inside and be alerted if the room gets too busy.

This challenge combines decision boxes, a counted variable and two inputs.

Pin	Direction	Device
D2	INPUT	Entry sensor (ON when a person enters)
D3	INPUT	Exit sensor (ON when a person leaves)
D8	OUTPUT	Display / counter output
D9	OUTPUT	Alarm (sounds when the gallery is full)

i	Set count = 0.
ii	Check the entry sensor (D2) — if ON, add 1 to count.
iii	Check the exit sensor (D3) — if ON, subtract 1 from count.
iv	If count > 10 (gallery full), turn the alarm (D9) ON, otherwise turn it OFF.
v	Output the count value to the display (D8).
vi	Repeat continuously.

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Challenge 4 — Can dispenser for a school in Fort William

A school in Fort William is fitting a coin-operated can dispenser in the common room and needs a control system that accepts 10p and 20p coins, dispenses a can once enough money has been inserted, and gives change if too much is paid.

This challenge combines a for…next counted loop with multiple inputs and a sequenced output.

Pin	Direction	Device
D2	INPUT	10p coin sensor
D3	INPUT	20p coin sensor
D4	INPUT	Dispense button
D8	OUTPUT	Can dispenser motor
D9	OUTPUT	Change/reject indicator light

i	Set total = 0.
ii	Wait for a coin — if D2 is pressed (10p) add 10 to total; if D3 is pressed (20p) add 20 to total.
iii	Repeat step ii until the dispense button (D4) is pressed.
iv	If total ≥ 30p: turn D8 ON (dispense can) — wait 1 s — turn D8 OFF.
v	If total ≠ 30p exactly: flash D9 (change light) 3 times — each flash 0.5 s ON, 0.5 s OFF.
vi	Reset total to 0 and repeat.