Design, Testing and Troubleshooting
Reading datasheets, keeping a design quiet, measuring a circuit, finding faults, and complete worked projects.
This guide is about the practice of electronics: choosing parts and checking them against their datasheets, laying out and grounding a design so it works in the real world, measuring a circuit, finding out why it does not work, and putting it all together in finished projects. It assumes the component knowledge from the other guides, and its pages use them in worked numbers. When a design is ready for a board, continue with PCB Design and Layout and, for building it, Soldering.
Start here: what do you need?
| I need to… | Go to |
|---|---|
| check a part against my circuit: limits, derating, tables and graphs | Reading Datasheets |
| keep a design quiet: return paths, decoupling, grounding and filters | EMC and Noise at Board Level |
| protect against static discharge, surges and spikes | EMC and Noise at Board Level |
| choose and use a multimeter, oscilloscope or logic analyzer | Test Tools and Fault Finding |
| follow a method for finding the fault in a circuit | Test Tools and Fault Finding |
| work through a flowchart for a dead board, a microcontroller that will not run, a load that does not switch, or a noisy reading | Troubleshooting Flowcharts |
| see complete designs worked through: LED driver, sensor node, motor controller, buck supply | Worked Projects |
| turn a working circuit into a printed circuit board | PCB Design and Layout |
A suggested order
Read the datasheets page first, then noise and testing; use the flowcharts when something does not work, and the projects to see everything together.
- Reading Datasheets: How to read a datasheet: absolute maximum against recommended ratings, electrical tables, graphs, packages and footprints, with worked checks on real part types.
- EMC and Noise at Board Level: Where noise comes from and how it gets in: grounding, decoupling, return paths, filters, ESD and surge protection, with worked numbers.
- Test Tools and Fault Finding: Multimeter, oscilloscope and logic analyzer use, and a step-by-step method for finding faults.
- Troubleshooting Flowcharts: Decision flowcharts for a dead circuit, a microcontroller that will not run, a motor or load that does not work, and noisy or unreliable behavior.
- Worked Projects: Four complete small designs with parts calculated from the theory: an LED driver, a battery-powered sensor node, a motor controller and a 5 V supply.
Quick reference: formulas
| Topic | Formula | Page |
|---|---|---|
| Junction temperature | TJ = TA + P × θJA | Reading Datasheets |
| Linear derating | Pallowed = Prated − k × (T − 25 °C) | Reading Datasheets |
| Slew-rate limit | SR ≥ 2π f Vpeak | Reading Datasheets |
| Capacitor self-resonance | fSR = 1 ÷ (2π √(L C)) | EMC and Noise at Board Level |
| Ground bounce | V = L × di ÷ dt | EMC and Noise at Board Level |
| LC filter cutoff | fc = 1 ÷ (2π √(L C)) | EMC and Noise at Board Level |
| ESD pulse current (IEC 61000-4-2) | I = V ÷ 330 Ω (8 kV: 24 A) | EMC and Noise at Board Level |
| Trace spacing (3W rule) | center to center ≥ 3 × trace width | EMC and Noise at Board Level |
| Average battery current | Iavg = Iactive × D + Isleep × (1 − D) | Worked Projects |
Calculators
- Ohm’s Law and Power Calculator: Any two of voltage, current, resistance and power give the other two.
- PCB Trace Width and Current Calculator: Trace width for a current and temperature rise.
- Battery Runtime and Pack Calculator: Battery life from capacity and load, and series and parallel pack sizes.
- LM317 Adjustable Regulator Calculator: Output voltage, resistor values and heat in an LM317.
Safety
- Never probe mains-powered circuits without an isolation transformer and proper training.
- Use a current-limited supply for the first power-up of any new board, and set the limit low.
- Discharge large capacitors before touching a power supply; they hold charge for minutes.
- Wear safety glasses when powering new or repaired circuits.
The other Electronics guides
- Electronics Fundamentals: The circuit basics every maker needs: Ohm’s law, resistors, capacitors, inductors, diodes, transistors and switches, with worked examples.
- Analog Circuits and Sensing: Op-amps, comparators and timers, and how to read, amplify and filter sensor signals: thermistors, RTDs, load cells and 4-20 mA loops.
- Digital Electronics and Microcontrollers: Logic gates, counters and timing, and the hardware around a microcontroller: power, reset, clocks, GPIO, level shifting, the ADC and buses.
- Power and Motor Electronics: Batteries and supplies, switching converters and thermal design, and driving DC motors, steppers, servos and solenoids.
- PCB Design and Layout: schematic to layout, stack-up, routing, return paths and design checks.
FAQ
Where do I start when a circuit does not work?
Look first, then measure the supply at the chip’s pins, then divide the circuit in half. Troubleshooting Flowcharts gives the order of checks.
How much of a datasheet do I need to read?
The first page, the ratings, the electrical table rows you depend on, the graphs for your conditions, the thermal data and the application information. Reading Datasheets shows how.
Do I need an oscilloscope?
Not at first: a multimeter finds most faults. A scope becomes valuable once you work with timing, noise, PWM or serial signals; see Test Tools and Fault Finding.
References
- Ott, H. W., Electromagnetic Compatibility Engineering, Wiley.
- Pease, R. A., Troubleshooting Analog Circuits, Butterworth-Heinemann.
- Horowitz, P. and Hill, W., The Art of Electronics, 3rd ed., Cambridge University Press.
- Manufacturer datasheets and application notes for the parts you use: they give the limits, pinouts and example circuits.
Last reviewed: October 2026. Values are typical: check the datasheets of the parts you use, follow the electrical code for mains work, and do not work on live mains equipment unless you are qualified.