Electronic systems applied

The power supply, the input devices, any signal conditioning, the processing stage, and the output drivers — plus whether anything measures the output.

The largest integrated circuit, usually with a crystal beside it and a programming header nearby. Everything else feeds it or is driven by it.

Thin tracks carry signals and thick tracks carry power, so the widest tracks run from the supply to the output devices.

Saying what each part contributes and which stage it belongs to, and finishing with whether anything measures the output.

A motor, gearbox, position sensor and control circuit in one unit that moves to a commanded angle and holds it. Use one wherever a precise position matters.

When the user needs specific information — a temperature, a countdown, a fault code. A light can say something is wrong and never what.

It carries far larger currents and keeps the two circuits electrically separate, which is what lets a 5 V controller switch a 230 V load safely.

The current. A chip pin supplies a few tens of milliamps — enough for an LED with a resistor and nothing else.

Bluetooth about 10 m at very low power; Wi-Fi tens of metres at moderate to high power; 5G kilometres at high power. Reaching further always costs energy.

Bluetooth needs only the other device. Wi-Fi needs a router and a network. Cellular needs a network operator, a subscription and a SIM.

Is it battery-powered and must it last? Is it mains-powered inside a building with a network? Does it move, or is there no local network to join?

Keep the core function working without the network — a doorbell should still ring from its button if the server goes away.

Voltage across the component with the circuit running; current in line with the circuit broken; resistance with the power off and one end disconnected.

It has a very low resistance, so it becomes a short circuit. That is why the current socket is separate and fused on almost every meter.

Frequency, waveform shape, pulse width and duty cycle, and short glitches. A steady 2.5 V and a 0-5 V square wave read identically on a meter.

Count divisions and multiply by the setting: four divisions at 2 V/div is 8 V; a cycle across five divisions at 1 ms/div is 5 ms, which is 200 Hz.

V = I × R, so I = V ÷ R and R = V ÷ I. P = V × I, so V = P ÷ I and I = P ÷ V.

Converting to base units before substituting — milliamps into amps, kilohms into ohms.

Total charge used per day in mAh, then divide the cell rating by it. A 2,000 mAh cell supplies 20 mA for 100 hours.

It decides the physical size of the part. A quarter-watt resistor dissipating half a watt runs hot, drifts in value and eventually fails.

Resistors: R = R₁ + R₂ in series, 1/R = 1/R₁ + 1/R₂ in parallel. Capacitors: C = C₁ + C₂ in parallel, 1/C = 1/C₁ + 1/C₂ in series.

It must be smaller than the smallest resistor in the combination. An answer larger than both means the wrong rule was used.

V_out = V_supply × R₂ ÷ (R₁ + R₂), with R₂ the lower resistor. 9 V across 10 kΩ and 5 kΩ gives 3 V.

Much smaller wastes current and heats the board; much larger makes the junction a high impedance that the next stage loads and that picks up interference.

A rounded box for start and stop, a parallelogram for input and output, a rectangle for a process, and a diamond for a decision.

Exactly two, both labelled YES and NO. Three outcomes need two diamonds in sequence, not three lines out of one.

Otherwise it reads its sensor once and stops, leaving the output in whatever state it was in. The loop is what makes it monitoring.

A gap between the switch-on and switch-off thresholds, drawn as two decision diamonds with different values — 25 °C to open and 22 °C to close.

The supply rails — positive at the top, 0 V at the bottom. Every branch then hangs between them, input on the left and output on the right.

The wires are connected. Crossing without a dot means no connection.

Without it the base takes whatever current the previous stage can supply, risking the transistor and stopping a divider working as a divider.

Coil in the low-voltage circuit, contacts as a separate switch in the load circuit, joined only by a dashed line — which shows the two circuits are isolated.

Accelerometer — motion and orientation. Ultrasonic — distance by echo timing. Photoresistor — light. Hygrometer — humidity and air temperature.

It measures distance without contact, works in the dark, and is unaffected by the colour of the obstacle.

Whether its output is analogue or digital, whether it needs a divider, whether it needs amplifying, and exactly where it physically sits.

A sensor in the wrong place reads the wrong thing perfectly. A thermostat above a radiator switches the heating off while the room is cold.

A 100 nF capacitor beside the supply pins supplies the brief surge when an output switches, so the rail does not dip and reset the chip.

A switch alone connects the pin to 0 V when pressed and to nothing when released. The pull-up gives it a defined level the rest of the time.

Reading a mechanical switch twice a few milliseconds apart, because it bounces on contact and one press would otherwise look like several.

A motor draws several times its running current at start-up. Sharing a rail with the chip drags the supply down and resets it as the motor switches on.

Two to the power of the number of inputs: four for two inputs, eight for three, sixteen for four.

Combinational output depends only on the inputs now. Sequential output also depends on the previous state, so it needs a latch, flip-flop or counter.

Eight plus zero plus two plus one is eleven. Each place is twice the one to its right: 8, 4, 2, 1.

When it must remember something — a latching alarm that stays on after the intruder has gone, a counter, or a response that depends on what happened before.