Sefism Embedded Systems and IoT Cheat Sheet

What this cheat sheet is

The Embedded systems and IoT cheat sheet is the quick-revision companion to Sefism's Embedded systems and IoT roadmap. It runs from C on bare hardware through circuits, buses, sensors, an RTOS, MQTT and dashboards to debugging and finishing a device, in ten chapters that match the roadmap's ten stages.

It is built for students and early-career engineers at the bench. Every concept has what it is, why it matters and the classic mistake, and many have a formula, a worked example or a short snippet for your board. The aim, in the sheet's own words, is to spot the classic mistake before it costs you a component or a week.

Three editions

Pick the edition for the board you are using:

• Arduino and ESP32: Arduino sketches with setup and loop, ESP32 ADC quirks, FreeRTOS on the ESP32, ESP32 panic and backtrace reading, and sleep modes.
• STM32: STM32CubeMX projects and the HAL, FreeRTOS tasks and stack sizes, connecting an STM32 to a network, SWD and JTAG debugging, and HardFaults.
• Raspberry Pi: GPIO with gpiozero, why Linux timing is not real-time, the lack of a built-in ADC, threads and asyncio, running as a systemd service, and reading logs on the Pi.

Shared material makes up most of each edition, which has 72 to 74 concepts. Every edition is public at its own address, so you can read the code for your board before signing up.

Chapter by chapter

1. C for embedded (7 concepts)

Fixed-width integers, bitwise set, clear, toggle and test, memory-mapped registers, volatile, pointers on hardware, flash, RAM, stack and heap, and const and static. Four of these come with code.

2. Electronics you need (7 concepts)

Ohm's law and power, the LED current-limiting resistor, the voltage divider, 3.3 V and 5 V logic levels, pull-up and pull-down resistors, common ground, and power supply and decoupling.

3. Microcontroller basics (up to 11 concepts)

Microcontroller versus single-board computer, the build, flash and run cycle, your board's starting point (Arduino setup and loop, a CubeMX project with the HAL, or gpiozero), GPIO modes, debouncing, timers and PWM, interrupts and ISRs, and non-blocking timing.

4. Protocols: UART, I2C and SPI (6 concepts)

UART serial, I2C and how to scan an I2C bus, SPI, choosing between the three, and RS485 with Modbus RTU for real equipment.

5. Sensors and actuators (up to 9 concepts)

Reading a datasheet, the ADC, your board's analogue quirks, sensor drivers and libraries, filtering and calibration, transistor and MOSFET switches, relays and mains safety, and motors, servos and drivers.

6. RTOS basics (up to 9 concepts)

The superloop versus an RTOS, FreeRTOS tasks and priorities and task stack size (microcontroller editions), queues, mutex versus semaphore, priority inversion and deadlock, and deferring work from an ISR. The Raspberry Pi edition swaps in threads and asyncio and running as a systemd service.

7. Wireless and IoT (up to 11 concepts)

Wi-Fi station mode and reconnecting, MQTT publish and subscribe, topic design, QoS levels, retained messages and Last Will, an MQTT client on the device, Bluetooth Low Energy and GATT, LoRa, LoRaWAN and cellular, device security basics, and over-the-air updates.

8. Cloud dashboards for devices (7 concepts)

Running a Mosquitto broker, payload format, time-series storage, Node-RED flows, dashboard options, alerts and hysteresis, and detecting offline devices.

9. Debugging hardware (up to 9 concepts)

Multimeter checks, the logic analyser, serial logging, the watchdog timer and brownout and power problems, plus your board's crash tools: SWD and JTAG debuggers, HardFaults on STM32, ESP32 panics and backtraces, or logs on the Pi.

10. Portfolio: a working device (up to 7 concepts)

The power budget, sleep and low-power modes, the bill of materials, enclosure and wiring, PCB design basics, measured results and the device write-up.

Rules of thumb and glossary

Each edition has eight rules of thumb: seven shared ones (check power, ground and the pin number before debugging code; design well inside the datasheet's operating conditions; keep interrupt handlers short; scan the I2C bus before writing a driver; put an id, a timestamp and units in every message; measure current before promising battery life; keep firmware, schematic, BOM and photos in one repository) and one for your board. The A to Z glossary adds 64 to 67 smaller terms, depending on the edition, to the sheet's concepts.

How to use it with the roadmap

• After each stage: read the matching chapter and try to explain every concept aloud. Anything you cannot explain without notes is the part to revisit.
• Before wiring something new: reread chapter 2 and the relevant sensor or protocol chapter. Most "my code is broken" problems are a floating input, a missing ground or the wrong logic level.
• While debugging: chapter 9 gives you the order to check things in, and chapter 4 tells you what a healthy bus looks like.
• Before an embedded technical round or a project viva: chapters 1, 4 and 6 cover topics that come up often, such as volatile, I2C versus SPI, and mutex versus semaphore.

How it works on Sefism

The public page at /cheatsheets/embedded-iot/ shows every chapter's title and introduction, with the first chapters open in full. Everything on Sefism is free to learn from. Keeping a cheat sheet is one of the few actions that uses credits; new members get starting credits when they join, and anyone learning seriously who runs out can ask for more. Keeping the sheet opens every chapter in the member area.

Following the Embedded systems and IoT roadmap also unlocks this cheat sheet, and your first roadmap is free. Inside the roadmap, topics link straight to the concepts in the sheet that cover them.

Related on Sefism

• The Embedded systems and IoT roadmap this sheet accompanies.
• Making Embedded Systems and The C Programming Language for chapter 1.
• FreeRTOS documentation for chapter 6, and Eclipse Mosquitto for chapters 7 and 8.
• sigrok PulseView for capturing buses in chapters 4 and 9.
• How do I become an embedded systems engineer?

Frequently asked questions

Does the sheet replace datasheets and reference manuals? No. It tells you what to look for in a datasheet and the mistakes to avoid. Your part's datasheet and your board's documentation stay the source of truth.

Which edition should I read if I use an ESP32 with ESP-IDF rather than Arduino? The Arduino and ESP32 edition. Its ESP32 concepts (ADC quirks, FreeRTOS tasks, panics and backtraces, sleep modes) apply to both, and chapters link to the ESP-IDF programming guide.

Is there anything here for PCB design? Chapter 10 has a PCB design basics concept as part of moving a device off the breadboard. It is an introduction, not a full PCB course.