Introduction to Microcontrollers

Introduction to Microcontrollers

The purpose of this blog post is to give readers an overview of working with Microcontrollers and successfully implementing them in projects. There are numerous information on Microcontrollers available out there but very few give a big picture of the implication of building a project around them from beginning to end for people who have never used them before.

What are Microcontrollers?

This is the first questions that came to my mind when I first started to get involved with Microcontrollers, what is a Microcontroller actually? In simple terms a Microcontroller is an electronic device which is used to provide control signals to one or more targets devices. The control signals can be used to do simple task such as switch on a led, a relay or it can be a more complicated form of control signal such as a serial protocol signal used to send data through a USB port for instance.

In order to send the control signals the Microcontroller has the ability to read input(directly or through specialized devices), process them if required and in certain circumstances use specialized internal/ external devices to generate the control signals.

To achieve the ability of generating control signals, a set of instructions need to be programmed into the Microcontroller.

A bit more on control signals

Now some practical examples of what you can do with Microcontrollers and their ability to generate control signals(Not exhaustive):

Control Signal	What can you do with them?	Side Note
Power control(PWM)	Motor Control for robots and drones	External Motor Driver devices required
	Power inverters(12V DC to 110/220V AC)	External power drivers required
	Sound generation	Not hifi grade but usable for audible alerts
Audio applications	Send signals to specialized IC's to control volume, tone or build a 5.1 or 7.1	Additional  external specialized ic required
	Control DSPs(Digital signal processors)	Additional  External DSP device required
	Digitally controlled equalizer	Additional  Digitally controlled equalizer ic required
	FM tuner	Additional Digitally controlled FM receiver ic required
	Spectrum analyzer	Requires a powerful Microcontroller
	FAT file system MP3 player(SD card, USB drive or Parallel IDE hard disk)	Might require external decoder ic or decoding done internally on Microcontroller. Use of proper external DAC recommended. FAT library required. For usb drive USB host grade microcontroller required
Instrumentation	Function generator	Additional DDS ic or specialized function generator ic required
	PC based or standalone Oscilloscope	A very ambitious one but feasible with proper external devices
	PC based or stand alone logic analyzer	Another ambitious one but feasible with proper external devices
	Digitally controlled bench Power supply	Good quality external DAC required on top of external power electronics
	Data loggers to pc or FAT based storage
PCB building	PCB UV exposure timers
	PCB etch temperature controllers	Use of PID logic recommended
	SMD soldering oven temperature control	Use of PID logic recommended
Infrared Remote control	Receive or transmit infrared signals	Some Microcontrollers feature built in infrared modules

What you see on the above list are some examples of what can be done with Microcontrollers. The areas of applications are actually wider than that. In commercial applications Microcontrollers find their application in anywhere from consumer electronics to industrial grade applications. 

Working with Microcontrollers let's get stated

Great now that you've had an idea of how far a Microcontroller can be used let's go further on what we need to put them to use.

Below is what you will need to work with a Microcontroller:

1) The Microcontroller IC itself:

 But shouldn't I consider a development board first? That's a tricky one but let me explain. Normally whenever you are building a Microcontroller based project you have to choose a Microcontroller IC first. The reason being that the Microcontroller IC you will choose will be the one sitting on your final circuit board with the other devices it will control. Unless you are buying a development board to do a single one off project I would highly recommend  finding the IC first. Below are some of the Microcontroller ICs that I use.

The next question that comes in is how to choose this Microcontroller IC? First and foremost consider the following:

i) What is/are the target devices to be controlled?

ii) Is the use of specialized in built modules required?

iii)  How big is your program and is there enough Flash Memory on the device to hold it?(More on this in simulation later)

iv) Are signal speeds/timing extremely critical and can a Microcontroller handle it? In certain circumstances you might need to revert to the use of CPLDs or FPGAs for directly handling the signals with a Microcontroller. An extreme case is when you might be building an oscilloscope or a memory controller. In those extreme circumstances the Microcontroller serves the purpose of only sending control signals to the CPLDs/FPGAs but not direct control of the target device itself.

v) What manufacturers build the Microcontroller you have chosen and do they have microcontrollers that fall within you specs?

vi) Do you have access to the selected Microcontroller support documents such as datasheet and the like?

vii) Last but not least is the Microcontroller(s) you have chosen already available from your preferred online seller or local seller? Is it in production or phased out? Is the price of the Microcontroller within your budget or is it unaffordable?

As a simple guide my approach is once I have decided on points i) to vi) above I go and look for the Microcontroller online. In case it is not available (and will often be for newly launched devices), I iterate back until I have reached a viable solution.

As you work with these devices, you will get more familiar with certain brands and will tend to stick to them.

2) The development environment and the programming language

If you have settled with you Microcontroller choice then comes the need to program it. There are two set of tools that are needed to write code for a Microcontroller:

I) A development environment

The development environment is where code is written. Most code written for Microcontrollers use  C/C++ language. Some Microcontroller provide a free development environment. you also have third party vendors that provide a development environment for free or paid. How you feel at ease with the development environment is up to you but you can go around downloading some and give it a try

II) A compiler

The compiler is the program that will take the code you have written and convert it into a form that's usable by your Microcontroller. Some development environment feature built in full fledge compilers for free, provide a time or code size limited compiler for free but a paid version is required for full use. From my experience unless you are building an extreme project, a code size limited version can be used for most projects. The table below at time of writing gives a good idea.

Platform/Manufacturer	IDE	Compiler
Microchip	Free	XC compilers-code limited free, full version paid
Arduino	Free	Free
IAR embedded workbench	*Free	Code or time limited, full version paid
Mikroelectronica	*Free	Paid
ST	Free	Paid
Coocox	Free	*Free uses GCC compiler
TI	Third party both free and paid	FREE GCC others paid
Keil	*Paid	Paid
ATMEL	Free	*Free uses GCC compiler

An important note here, the above is only provided as a rough guide based on information freely available on the net. This being said, as you see the world is not as simple as it seems but the choice is yours. In case you are embarking on a commercial project my advice is to go with the paid solutions as they feature more support and less time to market. In case you are a DIYer s a limited or fee version can do the job. You will also notice there is more paid in the compiler column than the IDE one. The reason behind being that it's the compiler that actually does the delicate job or converting your source code and also optimizing it for use on your Microcontroller.

  3) The programmer

If you have reached this step it means your Microcontroller is settled and thankfully your development environment and compiler as well. Now once you have finished writing your code, how do you get it into your Microcontroller? Well you need a programmer. What's the programmer? It's simply a hardware that you can purchase that connects to your pc through a port. Most often these days most programmers connect through a USB port. The programmer next connects to your Microcontroller through dedicated pins. From your development environment or an additional software you will be able to press a button that will send the compiled code to you Microcontroller. Below are some examples of programmers:

As you can notice both devices feature a USB port and a special connector for the Microcontroller IC. There are some manufacturer specific programmers, clone programmers and universal ones.

4) The development board

At last we get there. The development board is actually a printed circuited board that contains your chosen microcontroller. The development board can be used for placing connecting wires going to other add on modules or shields as they are called. The advantage of a development board is that the code can be sent to the microcontroller with a programmer without having to solder or setup basic connections. It also serves as a first level prototype that can give an idea of how the project is turning out. But as you get my point about the microcontroller IC I stated above this is just a prototype not your final circuit.

Development boards can be purchased direct from manufacturers. Below are two of them. some development boards also feature a build in programmer.  Sometime the programmer is hard wired to the microcontroller and cannot be used elsewhere sometimes they have jumpers that can be used to turn them into a standalone programmer.  some newer versions even have slots in the board where the programmer board can be snapped off.

In case you feel that manufacturer development boards are too expensive, an alternative is what I would call "OEM development boards".  You can find these easily online at smaller prices. Just be careful of the build quality sometimes the board costs the same price as a microcontroller and you might have ICs that were sent off the QC test to land onto those boards, but they do work well enough for prototyping.

In case you are feeling adventurous you can build your own development board. It's a cheaper alternative you will need to read the microcontroller datasheet to understand where power goes, what pins need bypassing, where the crystal oscillator goes e.t.c. You will also need a good PCB design software, proper power, signal and ground plane routing as is the case usually when designing a PCB. don't let yourself scared by SMD's they are just a package and a lot of people have been able to successfully design their own development boards with them.

It is to note as well that there as a lot of development packages available online that come with plenty of add on boards or have devices prebuilt. These boards are a very nice option in case you want to focus on learning all the aspect related to microcontrollers.

Finalizing your project

Once you are done with testing your code with your prototype its normally time to go for the final version. In case you are happy and everything works as expected you can start designing the final PCB. Actually in practice I have not been so lucky mostly in cases where I was building something complex. There have always been two issues I ended up facing most of the time:

i) Vibration, noise and stability

As I mentioned before, using development boars might require the use of wires and sometimes breadboard to connect to other devices. Very often it can be a headache as you are working and probing the circuit. Wires move, get disconnected accidentally. You hit the table and all the wires vibrate sending chaos to your circuit.

Another point is the signal frequency used by microcontrollers. For certain projects I had signals running as low as 2MHz to reaching nearly 100MHz and above. As such high frequencies using connecting wires can cause EMI to flow around. Breadboard is another source of high capacitance that in certain circumstances can be a pain to control. A simple case, you want to flash a led, fine no issues. Try to control a CPLD from a microcontroller and the CPLD in turn is controls a static RAM IC with thresholds going above 100MHz to sample live signals is a nightmare with connecting wires. Sometimes the connecting wires themselves can grow huge in number.

ii) Power supply and stability

Very often most programmers can supply the required voltages to a microcontroller. This can be set through the development environment.

Some development boards also feature power through a USB cable, external wall adapters or simply a proper power supply.

I have always had the experience of things working nicely at this stage. But when I would power the device from outside i.e. with its target power source, it was a different picture. I had automatic power resets or false reads. Properly designing and bypassing the power supply that will power the final device is critical may it be battery operated or mains operated.

I would also advise to have a separate power line for the microcontroller and or additional digital devices. Powering microcontrollers from analog supply is something I would not recommend for signal integrity. Additionally make use of external regulators. Although some microcontrollers feature built in voltage regulators don't solely rely on them.

The cleaner your microcontroller power supply is the cleaner your control signals will be. This being said without going to extremes, like building a Class A amp grade power supply for a microcontroller.

So how to get things cleaner with signaling and power supply? Well the answer that helped me a lot was to first design the PCB and then build a version of the PCB using project board with all the connections properly soldered. An example is shown below:

The above is an example prototype I used. After having tested all the aspects of the circuit with my development board, I built a first version of this board to test everything. The microcontroller is housed below the lcd display. A supply cap and regulator is visible bottom left and the rest is next to the microcontroller pins below the lcd. It was only through this circuit that I was able to stabilize my signals and corrected power supply related problems. Some signal lines also had to be re routed.

Conclusion

I hope this article has been able to help shed some light on microcontrollers and how you use them and the process involved. I know some people get scared or run away from microcontrollers because it seems like a beast to daunt in itself. The subject does require some time and patience but you will surely get there. Microcontrollers are there and improving everyday and being able to use such fantastic devices in your projects can only mean you can build more interesting and ambitious projects.

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