Before I get practical and show you step by step how to actually use microcontrollers in your projects, let’s start with a quick overview, and clarify some basic terminology so we all are on the same page.
Microcontroller
A microcontroller is basically a chip. From the outside, it doesn’t look any different than other chips. Depending on the complexity of the microcontroller, the chip may come in an unexcited DIP8 case, or it comes as a large flat sophisticated SMD case.
For a microcontroller to work, it requires just a few external components:
- Crystal: a crystal is needed to provide a stable clock signal unless it is a very simple microcontroller running at low clock speeds such as an ATtiny that uses an internal oscillator instead.
- Voltage Regulator: since microcontrollers are sensitive towards voltage and can be destroyed when too high a voltage is supplied, a voltage regulator ensures that the required voltage is supplied.
- Capacitors: Decoupling capacitors need to be placed close to the power pins of the microcontroller to filter out noise and stabilize the power supply.
- Reset Circuitry: a button and a pull-up resistor are needed to ensure that the reset pin is disabled unless the button is pressed.
Supply Voltage
Microcontrollers require an exact supply voltage and can easily be destroyed when connected directly to *too much voltage**.
Older microcontrollers use a 5V supply voltage whereas most modern microcontrollers use 3.3V.
Memory
Most microcontrollers come with various types and sizes of memory built-in. The flash memory is the most important type of memory as it is the place where code can be stored. Flash memory is non-volatile (data stays intact when power is turned off) and works very similar to ordinary SD Memory Cards.
In DIY, microcontrollers today should have at least 4MB Flash memory, or else they can only be used for very simple tasks and might not integrate well in DIY Home Automation solutions.
Firmware
The software that tells the microcontroller what it should do is called firmware and resides in non-volatile Flash memory.
When you power on or reset the microcontroller, it immediately starts executing the firmware code.
- Firmware can be preloaded on the microcontroller (i.e. on NodeMCU boards) or uploaded manually at any time.
- Firmware is offered by many parties and then typically does fairly specific things (like control LED strips), or can be written yourself using an IDE (Integrated Development Environment) like Arduino IDE or platformio.
Boot Loader
Every microcontroller has some basic code that is either safely stored in ROM or in a protected section of its Flash memory: the boot loader.
When the microcontroller is instructed to run the boot loader, it invokes its service interface: you can now manage the microcontroller and i.e. upload new firmware to it.
The procedure to switch a microcontroller to boot loader mode varies by type. For example, on ESP32-based microcontrollers, you need to pull GPIO0 low while resetting the microcontroller.
Typically, the tools you use to upload new firmware handle this automatically.
Clock
All microcontrollers internally use a clock. This is not a regular clock to tell the time but rather an oscillator with a certain frequency. The microcontroller executes one command at a time, and the clock sets the rate at which this occurs.
Some microcontrollers use an internal oscillator while others require at least an external crystal to set the clock frequency.
GPIO
A GPIO (general-purpose input/output) is a pin on a microcontroller that can be programmed to function as either an input or an output. When in input mode, it can read signals (i.e. button states) and often even voltages in a given range. In output mode, it works like a switch and can switch between low and high (i.e. to relais, lamps, transistors).
GPIOs can be switched on and off in very high frequency. This can be used to dim LEDs (using PWM), or to implement control protocols such as I2C or SPI. Control protocols can be used to transfer large amounts of data, i.e. to work with displays or storage.
In a nutshell, the more GPIOs a microcontroller exposes the more things you can control simultaneously.
Microcontroller Modules
To make life easier for developers, companies like Espressif ship their microcontrollers as modules that come with most of the required external components in place, minimizing the work in hardware development.
Such modules add a crystal, Flash memory, an antenna or antenna jack (if the microcontroller is WiFi-enabled), and sometimes they cover the components with a metal cap that shields RF.
Development Board
Development boards make life a lot easier for developers and hobbyists as well.
Development boards are small PCBs that come with everything needed to safely run a microcontroller out-of-the-box. They add the following to the microcontroller chip:
- USB Connector: connecting the microcontroller to a computer (i.e. to upload new firmware or communicate with it)
- USB-to-Serial Chip: most microcontrollers internally use a simple serial interface to communicate with the outside world. Most computers have replaced serial connectors with USB ports. A USB-to-Serial Chip translates the USB signals to serial signals.
- Voltage Regulator: makes sure that you do not toast the microcontroller by supplying the wrong voltage. The valid input voltages depend on the type of voltage regulator. At minimum, the USB-delivered 5V are safely changed to the input voltage the microcontroller requires.
- Anti-Noise: variety of capacitors and other discrete components that stabilize the voltage and minimize electrical noise on the lines.
- Buttons: development boards come with a Reset button (hooked up to the microcontroller Reset pin). Some boards have another button labelled Boot. By holding the Boot button on ESP32 boards, resetting the microcontroller launches the internal boot loader.
- LED: Most development boards come with a power LED (lights up when the board is using its internal voltage regulator), and a user-programmable second LED prewired to one of the GPIOs. Can either be a simple LED or a WS2812 programmable RGB LED. Used for easy status indication, and to provide user feedback. There are development boards without such LED (i.e. DevKitC V4).
- Crystal: If the microcontroller is requiring an external crystal, the board supplies it and drives the clock.
NodeMCU
Some development boards carry the term NodeMCU in their name. On the hardware side, they are regular development boards. However, they always come with special firmware preloaded. Here are the facts you should know about NodeMCU:
- ESPxxx Microcontroller: NodeMCU development boards always use an ESP8266 or one of the ESP32-family microcontroller because the bundled firmware requires it.
- eLUA Interpreter: The preloaded (bundled) firmware runs an eLUA Interpreter. By connecting to the board via USB, you can send scripts written in the language LUA to tell the microcontroller what to do. So you do not necessarily need to program own firmware and upload it.
Most users aren’t even aware that NodeMCU development boards come with a bundled LUA firmware. They ignore the firmware part of the deal and treat NodeMCU development boards like a generic development board: most typically, they upload own firmware, essentially overwriting and deleting the bundled LUA firmware without using it.
Flasher
Flashing is the process of uploading new firmware to the microcontroller.
A flasher is a tool that performs this process: it can take a firmware file and upload it to the flash memory of a microcontroller. The microcontroller then starts executing the new firmware after a reset (that is typically part of the uploading process). Note that the flasher program must match the type of microcontroller you use and is typically provided by the microcontroller manufacturer.
- You use a flasher only when want to upload a firmware file that you got from someone else.
- When you program your own firmware using one of the available free development environments such as Arduino IDE or platformio, the flasher is part of the IDE and transparently works in the background.
[!TIP:] A very convenient way of uploading new firmware to a microcontroller is web based flashing that surfaced only a few years ago: it works right from within a Chrome browser (other browsers do not yet support this feature), requires no prerequisities or installations, and is very simple to use. You’ll find many examples in the remaining articles.
IDE (Integrated Development Environment)
Programming firmware yourself provides the maximum control and flexibility: you decide completely on your own what (and how) a microcontroller should behave, and you can freely use all of its features. That’s because you are essentially writing the entire software that the microcontroller gets to see.
On the flipside, you need to do all the work yourself. Luckily, programming new firmware is no rocket science though, thanks to modern tools and free libraries. It does require basic programming skills.
Writing Code
One of the most important tools required is a IDE (Integrated Development Environment). It basically does these things:
- Write Code: provides an editor in which you can write and test the code. The programming language is always C++.
- Libraries: provides help in finding available free libraries that add specific commands to manage the components you are using (display drivers, sensors, LED strips, etc.)
- Samples: provides sample code that you can use as a start, then customize
- Compile: can compile your code into a binary firmware image that matches the type of microcontroller you are working with
- Upload: can upload the firmware you created to your microcontroller
- Monitor: provides a console or terminal to display the information sent back from the microcontroller over the serial interface, and to send back user input
Two Free Choices
There are two popular IDEs used by DIY hobbyists: Arduino IDE and platformio. They both take care of all of the tasks listed above, and they both work with the same wide variety of microcontrollers.
[!TIP:] Choosing an IDE is a matter of personal taste and preference. Some users use both side-by-side, and choose the IDE depending on what they plan to do. Arduino IDE is very simple to use but gets confusing when your projects grow. platformio targets professional developers but requires a few steps to set it up correctly and understand its *project structure.
Other Development Environments
While the IDEs that I just mention are used to create and upload completely new firmware, there are other development environments that do not touch the existing firmware but rather work with it.
For example, NodeMCU development board come with its integrated LUA firmware. You can use a LUA development environment to talk to this firmware and send it jobs in the shape of LUA scripts.
Instead of creating and changing firmware on the lowest level, the LUA development environment lets you compose LUA scripts, send them to the *LUA interpreter running in your NodeMCU default firmware, and communicate back and forth with the interpreter.
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(content created May 01, 2024 - last updated May 26, 2024)