Circuit Construction
Back to Electronics hub GlossaryThis is the Circuit construction area of the course: decoding resistor values, choosing the right board and wiring, soldering safely, and completing circuit and layout diagrams.
Resistor values: colour code & BS1852
- Colour code (three colour bands + a tolerance band): bands 1 & 2 are digits, band 3 is the multiplier, and the tolerance band gives the ± range.
- BS1852 / R-notation: the letter (R, K or M) does two jobs. It gives the size — R = ohms, K = ×1000, M = ×1 000 000 — and it marks where the decimal point goes. Examples: 270R = 270 Ω, 5K8 = 5.8 kΩ, 2M7 = 2.7 MΩ.
- Tolerance: the real resistor can be a little above or below its label. Tolerance tells you the highest and lowest it could be.
On a 4-band resistor, bands 1 and 2 are the and band 3 is the . For a circuit you expect to change many times, the best board is a .
The letter (R, K or M) replaces the decimal point and sets the size.
See the full answer
Write 4 700 Ω and 5 800 Ω in BS1852 notation, and give the resistance band sequence for 4.7 kΩ (yellow, violet, red).
Answer
Boards: prototype, stripboard & PCB
| Board | Connection | Best for |
|---|---|---|
| Prototype (breadboard) | push-fit, non-permanent | quick testing & changes |
| Stripboard | soldered onto copper strips (tracks cut where needed) | a permanent one-off build |
| PCB | soldered to a printed copper layout | reliable, repeatable production |
State which board you would use to test an idea you expect to change several times, and why.
Answer
Soldering safely & non-permanent methods
- Return the iron to its stand the moment you are not using it.
- Solder in a well-ventilated area or use fume extraction — never breathe the fumes.
- Hold work in a clamp or stand, not your fingers, and let joints cool before touching.
- Wear eye protection and wash your hands afterwards.
Permanent joints are made by soldering; non-permanent joints use prototype boards, screw terminals or plug/socket connectors.
State two safety measures you must follow when soldering a circuit.
Answer
Cables & wiring
| Cable | Use |
|---|---|
| Multi-strand | flexible connecting wire that bends without breaking |
| Ribbon | many parallel cores for neat multi-way connections between boards |
| Co-axial | a screened signal cable that resists interference |
| Fibre-optic | carries data as light — fast and immune to electrical interference |
Wiring conventions on a build
Follow these conventions so a board is neat, reliable and easy to fault-find:
| Convention | Why / where |
|---|---|
| Single-core wire | for Wye links and permanent connections on the board — holds its shape and lies flat. |
| Multicore (stranded) wire | for flying leads — connections that flex or move (to switches, off-board parts) without the core snapping. |
| Colour coding | identify each signal at a glance: red = +, black = 0 V, and a distinct colour for each other signal. |
| Joining separate boards | use crimped connectors or terminal blocks so boards can be linked and unplugged cleanly. |
| Spiral wrap & cable ties | gather wire bundles together and keep them tidy, so wires don't snag or pull on their joints. |
- Securing & looming: bundle wires together and hold them in place with cable ties, a spiral wrap, heat-shrink, cable lacing / a loom, or P-clips — so wires don't pull on their joints, snag or get trapped.
- Advantage of colour-coding or numbering: each wire is easy to identify, so it is quicker to connect correctly and to fault-find.
- Examples of where it's used: mains plug wiring (brown = live, blue = neutral, green-yellow = earth); the red stripe on ribbon cable marking pin 1; resistor colour bands; and numbered terminal blocks / network cables.
(a) A signal must travel a long way without picking up electrical interference — state a suitable cable. (b) State one valid way to secure a bundle of wires. (c) Give one advantage of colour-coding wiring and one example of where it is used.
Answer
Circuit ↔ layout diagrams & missing components
- A circuit diagram shows components as symbols and how they connect electrically.
- A layout diagram shows where each part physically sits on the board and how the tracks/wires run.
- You must be able to convert between the two, and complete a circuit diagram from a specification by adding any missing components (using the symbol reference).
A specification says an LED must be protected from too much current. Its circuit diagram shows only the LED and supply. State the missing component and where it goes.
Answer
Solder Master — read the colour code
Read each resistor's four bands and pick its value. Bands 1 & 2 are digits, band 3 is the multiplier, the gold band is ±5% tolerance. Score 8 / 10 to earn the 🪛 Solder Master badge.
Check your understanding
Answer the multiple-choice questions, then mark yourself with the RAG self-check.
RAG self-check
Tap Red / Amber / Green for how confident you feel.