Problem-solving recipes

A step-by-step procedure for every problem type this course teaches — what to do first, what to do next, and how to tell which case you're in.

What are you being asked to do?

What is in front of you right now?

You're about to buy or plan something → Choose a board for a project, then Check a board listing before buying. Someone has described a whole device in everyday words → Plan a small embedded project from a request.
You have a number to read or convert → a value with the wrong prefix: Convert between SI prefixes; coloured bands: Read a resistor's colour code; a limit for a chip: Answer a design question from a datasheet.
You're choosing a part's value → an LED: Size an LED's series resistor; a voltage too high for a pin: Scale a voltage down for an input pin; a delay or a slow filter: Size an RC for a delay or a filter; smoothing PWM into a steady voltage: Size an RC filter for PWM; a coil: Choose and fit a flyback diode; a supply at the wrong voltage: Choose a regulator for a board or module.
A pin has to turn something on → first Can this pin drive it directly? If not, an NPN switch: Size an NPN base resistor; a DC motor: Wire a DC motor to a board safely.
You're wiring power or two boards together → a battery or adapter: Power a board from something other than USB; a 3.3 V part and a 5 V part: Connect a 3.3 V part and a 5 V part; a schematic to build: Build a schematic on a breadboard. Before every power-up: Check a circuit before you power it. Something already misbehaves and the firmware is known to work: Find a wiring fault.
The computer and the board aren't talking → no port, or the wrong one: Find the port your board is on. A normal upload: Upload firmware to a board. An upload or a sketch that fails: When an upload fails, in order.
Firmware has a raw reading → an ADC code: Turn an ADC reading into a real-world value; a thermistor: Turn a thermistor reading into degrees; an ultrasonic echo: Turn an echo time into a distance. Readings steadily off: Calibrate a sensor with two reference points; readings noisy: Choose an EMA's alpha. Still choosing the sensor: Check a sensor against your board and your project.
It runs on a battery → one steady current: Estimate a battery's life, best case; a device that sleeps and wakes: Estimate battery life from a duty-cycle table; charged by the sun: Size a solar panel and battery for a small node.

Planning and buying

Choose a board for a project

Use when: you are about to buy or pick a board for a specific project

Goal: a named board and variant whose datasheet confirms every requirement

Choosing a board

Check a board listing before buying

Use when: you are about to buy a clone, a compatible board, or any board not sold by its maker

Goal: a listing whose chip, USB, voltage, pinout and schematic you have confirmed, or a reason to walk away

Buying parts wisely

The second check, on the specific listing you're about to pay for.

Plan a small embedded project from a request

Use when: someone describes a device in everyday words and you have to build it and prove it works

Goal: a written plan whose every requirement has a test, and a build order that always leaves a working device

Engineering a project

The capstone procedure, from a spoken request to requirements, tests and a build order.

Reading numbers and documents

Convert between SI prefixes

Use when: a value is written with one prefix and you need it with another, or you need to compare two values with different prefixes

Goal: the same quantity written on the rung you need

Units, prefixes and scientific notation

Read a resistor's colour code

Use when: a through-hole resistor shows coloured bands and you need its value and tolerance

Goal: the resistance in ohms and the range its real value may fall in

Resistors in practice

Answer a design question from a datasheet

Use when: you need a voltage, current, pin or time limit for a chip before wiring or writing firmware

Goal: a number you can design on: the right table, a guaranteed column, and conditions that match your circuit

Reading a datasheet

The right table, a guaranteed column, and conditions that match your circuit.

Choosing part values

Size an LED's series resistor

Use when: an LED is powered from a fixed voltage (a supply rail or an output pin driven HIGH) and needs a resistor in series

Goal: a standard resistor value, the current it gives, and a confirmed power rating

LEDs and current limiting

Scale a voltage down for an input pin

Use when: a signal or supply is higher than the voltage a board's input pin is allowed to see

Goal: two resistor values whose output stays inside the pin's safe range at the highest input, without wasting much current or being loaded down

Voltage dividers

Size an RC for a delay or a filter

Use when: you need a capacitor voltage to take a chosen time to rise, fall, or settle

Goal: an R and C from your drawer whose time constant gives the delay you want

RC time constants

Choose and fit a flyback diode

Use when: a relay, motor, solenoid or other coil is switched on and off

Goal: a diode whose ratings cover the coil, fitted the right way round

Diodes

Choose a regulator for a board or module

Use when: a circuit needs a steady voltage from a supply or battery at a different voltage

Goal: an LDO or a switching regulator that keeps the output steady at the lowest input and stays cool at the highest

Voltage regulators

Size an RC filter for PWM

Use when: a PWM pin must give a nearly steady voltage, for a reference, a slow analog input, or a sensor test

Goal: a filter whose ripple is small enough and whose response is fast enough, at the highest PWM frequency available

From PWM to analog

An RC sized for ripple and response time together, at the highest PWM frequency.

Switching loads from a pin

Can this pin drive it directly?

Use when: you want a pin to turn something on, and need to know whether it may connect straight to the pin

Goal: a yes with a calculated current under the pin's limit, or a clear no that sends you to a switch

GPIO is not a power supply

Always first. A clear no sends you to one of the two below.

Size an NPN base resistor

Use when: a pin switches a load through an NPN transistor in a low-side switch

Goal: a standard resistor value that saturates the transistor while keeping the pin under its limit

The transistor as a switch

Wire a DC motor to a board safely

Use when: a board's pin must turn a brushed DC motor on and off, in one direction

Goal: a circuit where the pin only signals, the motor's current comes from its own supply, and no spike or sag reaches the board

Driving motors safely

A logic-level MOSFET, a flyback diode, bulk capacitance and a separate supply.

Power, wiring and faults

Check a circuit before you power it

Use when: you have built or changed a circuit and are about to plug in USB or a battery

Goal: power applied only to a circuit that matches its plan, with no short across the supply

A safe workspace

Before every power-up, not only the first.

Build a schematic on a breadboard

Use when: you have a schematic and an empty breadboard, and need to know where every leg goes

Goal: a layout where every net is one strip or rail and every part spans the right two nets

Reading schematics

Power a board from something other than USB

Use when: a project needs a battery, an adapter or a bench supply instead of, or as well as, a USB cable

Goal: one source per rail, within the input's rated range, with every ground joined

Powering a board safely

Connect a 3.3 V part and a 5 V part

Use when: two chips that run at different supply voltages share one or more signal wires

Goal: every signal read reliably in both states, with no input pushed past its absolute maximum

3.3 V vs 5 V and level shifting

Find a wiring fault

Use when: a circuit misbehaves, resets, runs hot or does nothing, and the firmware is known to work

Goal: the faulty connection found with nothing further damaged

Protection and wiring failures

Getting firmware onto the board

Find the port your board is on

Use when: you need to choose a port for an upload or a serial monitor and aren't sure which entry is your board

Goal: the one port name that belongs to your board, confirmed by unplugging it

Ports, drivers and permissions

Upload firmware to a board

Use when: you have a sketch that compiles and a board on a USB cable, and want the board running it

Goal: the board running the new program, confirmed by what it does

Bootloaders and uploading

When an upload fails, in order

Use when: a sketch won't compile, won't upload, or uploads but doesn't work, on an Uno R4 Minima or an ESP32-S3-DevKitC-1

Goal: the one stage that failed, found and fixed, with every earlier stage known to work

When flashing fails

When any stage fails. Works through the stages in order, from compile to running.

From raw readings to real values

Turn an ADC reading into a real-world value

Use when: firmware has a raw ADC code and needs a voltage, or the temperature, light level or battery voltage behind it

Goal: the quantity the sensor measures, with the arithmetic in the right order

How an ADC works

Check a sensor against your board and your project

Use when: you are choosing a sensor, or about to wire one you already have

Goal: a yes or no for this board and this job, with the reason

Reading a sensor datasheet

Turn a thermistor reading into degrees

Use when: an NTC thermistor sits on top of a fixed resistor in a divider, read by an analog pin

Goal: the temperature in °C, from the ADC code (or millivolts) and the thermistor's datasheet numbers

Temperature and humidity

A divider, then the ADC, then the beta equation.

Turn an echo time into a distance

Use when: an ultrasonic module reports a round-trip echo time

Goal: the distance to the target in centimetres, corrected for air temperature

Distance and proximity

Calibrate a sensor with two reference points

Use when: a sensor's readings are steadily off, and you can put it beside two known values

Goal: a gain and an offset that turn every raw reading into a corrected one

Calibration

Choose an EMA's alpha

Use when: you want an EMA that settles in a chosen time, at a known sample interval

Goal: an alpha that gives the wanted time constant, and a check of the lag it costs

Noise and filtering

Batteries and energy

Estimate a battery's life, best case

Use when: a circuit runs from a battery labelled in mAh and you know, or can measure, its average current

Goal: an upper bound on running time in hours, and the battery's energy in Wh

Power, energy, and heat · extended later in this course

One steady average current against a battery's capacity.

Estimate battery life from a duty-cycle table

Use when: a device repeats a cycle of states (sleep, measure, send) and runs from a battery

Goal: an average current and a battery-life estimate, each with its sources and assumptions stated

Power budgets

Extends the recipe above to a device that sleeps, measures and sends. The more complete version.

Size a solar panel and battery for a small node

Use when: a duty-cycled device with a known average current should run on solar power through the whole year

Goal: a panel rating and a battery capacity, each with the assumptions that produced them

Solar and energy harvesting