What Is a Microcontroller? Programming an Arduino Board

Typical Arduino development board
H0dges, public domain via Wikimedia Commons

What Is a Microcontroller?

You probably have lots of these in your home, although you don’t know it! A microcontroller is a type of computer in the form of an integrated circuit (IC) or “chip,” which is often used in devices in your home which incorporate electronic circuitry. You have probably heard of microprocessors, e.g. Intel Pentium, and these are used as the CPU (Central Processing Unit), effectively the “brain”, in a computer. Microprocessors are integrated circuits that process the instructions in a computer program, perform calculations and send data to and from memory and disk. A microcontroller is a specific type of microprocessor. It differs from a normal microprocessor in the following ways:

• It has built-in “I/O” (input/output) capabilities, so it can read and write digital and analogue values/states and connect directly to the “real world”. A microcontroller, unlike a microprocessor, can connect directly to switches, buttons, LCD displays, LEDS, relays and serial ports.
• Microcontrollers are generally used for low-to-medium complexity specific tasks in equipment. This contrasts with the powerful, number-crunching microprocessors used in PCs, which handle a variety of software applications.
• Microcontrollers are often used in portable devices which run on batteries, e.g. digital cameras. So they are often low-powered with a small current consumption (unlike the heat-sinked, fan-cooled microprocessor in a desktop computer.)
• Compared to the microprocessor in a PC, the RAM within a microcontroller can typically range from 64k down to as little as 1k.
• The program in a microcontroller is usually stored in EPROM or EEPROM. This is a type of nonvolatile (a program that doesn’t disappear when the device is turned off) memory which can be continuously wiped and rewritten.

DIL (Dual In Line) integrated circuits (ICs) or “chips”
Kimmo Palosaari, public domain image via Wikimedia Commons

Microcontroller Uses

Lots of devices make use of microcontrollers. Some examples:

• Burglar alarms incorporate a microcontroller chip which is connected to the keypad, display and sensor/contact inputs. Microcontrollers are generally self-contained chips with the ALU (Arithmetic Logic Unit), memory and I/O all contained within one integrated circuit.
• Older automatic washing machines used a cam switch for sequencing the operations during a wash cycle. This was quite a complex switch and was mounted on the end of the shaft of the knob you used to select a wash program. Newer machines use a microcontroller to sequence operations. Other appliances, such as microwave ovens and dishwashers, may incorporate a microcontroller.
• TVs use microcontrollers to handle the selection of channels and read the state of buttons on the TV.
• Microcontrollers are used for engine control and the display of information on the dashboard (fascia) of vehicles.
• Digital cameras use microcontrollers to handle input from buttons and control image capture and display.

Microcontroller Examples

Some commonly used microcontrollers:

• Zilog Z8
• Intel 8051
• Texax Instruments TIMSP430
• Atmel AVR

What Is an Arduino?

Arduino is an open-source hardware/software programming platform and brand, based around Atmel microcontrollers. It was a concept developed by a company founded in Italy in 2005. Open source means that circuit schematics and source code of the software used in Arduino modules are freely available and can be modified by enthusiasts. 
The Arduino company, headquartered in Monza, and acquired by Qualcomm in 2025, still produces microcontroller boards which you can buy online. Since Arduino is open source, you can also buy clones of these boards.

Arduino development boards, with their analogue and digital inputs and outputs, are ideal for artists, designers and electronic hobbyists who wish to put together a system without having to know a huge amount about digital design. Input and output signals are made available on the Arduino board using rows of female connectors into which individual leads or single in line (SIL) connectors can be plugged.

An Arduino development board will have at least:

• Nine digital pins which can be either input/output channels. Some of these can be set up as PWM (Pulse Width Modulation) outputs. A PWM signal is a square wave whose pulse width can be varied. PWM is used for speed and position control of motors and servos in robotics and remote control applications
• Four analogue input channels
• At least one serial port which may also be used to download code to the Arduino

Some boards also have a range of analogue output channels.

There is a high degree of flexibility as regards the function of pins, some of which can be configured as either analogue or digital. Digital pins can be configured as either input or output.

Arduino boards sense the environment around them as they receive input from sensors connected to these analogue and digital inputs. They can also control actuators such as motors, alarm sounders and electric valves or switch on LEDS, lamps or other visual indication devices. The output drive capability of outputs is limited, so usually, transistors, FETS, or relays must be used between the Arduino output pin and the driven device. An output is capable, however, of driving LEDs directly.

The connectors on board are arranged in a standard manner so that shields can be connected. Shields are modules with a dedicated function (e,g, infrared output, Bluetooth, GSM, WIFI, Ethernet, motor on/off control using relays, stepper motor control). Depending on the shield type, it may be possible to stack several shields on top of each other and address them individually over an I²C serial bus.

Since the Arduino code and hardware is open source, third-party developers have produced clones of the official Arduino boards.

Arduino boards have from 32 to 512k of flash memory which can be used for program storage.

This is Leonardo, one of the ranges of Arduino boards. Digital pins can be configured as either input or output. Several digital pins can double up as analog inputs in addition to the standard analog inputs
© Eugene Brennan

What Can an Arduino Board Be Used For?

An Arduino board can be used for doing lots of cool stuff. You can easily add LCD displays, a keypad or seven-segment display modules and build a simple system quickly. Lots of information and libraries are available on the Arduino.cc website. You can design your own add-on electronics or use shields to build a modular system. Arduinos, because of their versatility, can be used for simple, mundane tasks or complex applications.

An example of a simple application would be the ability to turn on a device when the temperature in a room falls below a certain level. It wouldn’t be too difficult to extend this application and add a GSM module which could send out a text message when this occurs. Arduino boards can be used to implement a complex home automation system which could be controlled over a smartphone.

They are also used by enthusiasts as the processing and control device in robots, and kits are available for building a simple wheeled robot.

Microcontroller Projects: Programming an Arduino Board

Arduino boards are programmed in C and high-level functions are provided as standard for reading and writing to analogue and digital pins and serial ports. Source code is known as a “sketch”. Standard libraries are also available for tasks such as output to an LCD panel or communication with a GSM module. Lots of other libraries and code have been contributed by enthusiasts and are available on the Arduino website.

A basic code editor/compiler is available on the Arduino website, which can be used for developing programs. However, the editor is basically just like Wordpad and doesn’t provide any colour-coded highlighting or have sophisticated debug features. Atmel Studio, a cut-down, customised version of Visual Studio, is an alternative which provides these features.

Programs are downloaded onto an Arduino board using either a serial port or USB connection. A bootloader then loads the program into memory on reset so that an external programmer isn’t required.

Simple Arduino Sketch

// A simple sketch written in C which can be run on an
// Arduino board. It reads a character from the serial port, echos
// it back to the remote terminal and flashes an LED

void setup()

{
Serial.begin(9600) // Open the port at 9600 baud
pinMode(13,OUTPUT) // Set pin 13 as an output
}

void loop() 
{
char character;

if(Serial.available()) // if there is data in the receive buffer.....
{
character = Serial.read(); // read the character
Serial.write(character); // echo the character to the serial port

// Flash an LED
digitalWrite(13,HIGH); // turn on the LED connected to pin 13
delay(50) // delay 50 mS
digitalWrite(13,LOW); // turn off the LED connected to pin 13

}

Which Arduino to Buy?

For kids and absolute beginners, I recommend the Grove Beginner Kit, available from Amazon. It’s an all-in-one Arduino Uno-compatible board with 10 Sensors & 12 Projects. Interestingly the board is supplied with breakout sections for each transducer which can be detached if desired. Jumper cables are supplied to connect the main controller board to each transducer section:

Grove Beginner Kit
Amazon

Transducers in the Grove Beginner Kit Include:

Sensors

• Light Sensor
• Sound Sensor
• Temperature & Humidity Sensor
• Air Pressure Sensor
• 3-Axis Accelerator

Actuators

• LED
• Buzzer
• OLED Display
• Button
• Rotary Potentiometer

The first Arduino board I bought was the Arduino Leonardo, also available from Amazon (explained earlier). It has a modest amount of I/O including 20 digital I/O ports, 7 pulse width modulation (PWM) channels, 12 10-bit analogue input channels. Headers are soldered onto the board, but you may be able to find a version without them if you need more space.

Arduino Leonardo
Amazon

In addition to an Arduino board, you need a way of displaying information such as measured values from a sensor, typed text or status messages. Two useful modules are:

• 16 character x 2 row LCD Serial Interface Adapter Module available from Amazon
• 4 character 7 segment display available from Amazon

16-character, 2-row display for Arduino
Amazon

4-character, 7-segment display
Amazon

Comduino Terminal Application

Comduino Terminal, an example Windows application I wrote for a Leonardo Arduino board. A user can communicate with the board over a USB or serial link, telling it to set digital inputs high or low, set analogue outputs, and read from digital and analogue inputs.

This is Comduino Terminal, an application for reading and writing Arduino I/O pins. It is available on my blog (check my profile for the link).
© Eugene Brennan

Disclaimer

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2014 Eugene Brennan

Comments

zafrinazara on August 16, 2019:

Thank you for giving me a wonderful explanation about Arduino microcontrollers. We also conduct embedded system course in chennai for all streams of engineering students using sensors and microcontrollers.

PDXBuys from Oregon on December 01, 2014:

If I am lucky Santa will bring me one of these for Christmas.

How To View What's Behind Your Washer Drum

© Eugene Brennan

You can check what's between the inner and outer drums of a washing machine, or check for limescale build-up on the heating element, by spinning the drum and illuminating it with a bright torch.

What Are Voltage Regulators Used For?

78XX series of voltage regulators. E.g. 7805 and 7812 having regulated outputs of plus 5 volts and plus 12 volts respectively. Silverxxx, CC BY SA 3.0 Unported via Wikimedia Commons.

We're surrounded by electronic gadgets and appliances, and even devices that don't appear to be electronic may use electronic circuitry internally. For electronics to work properly, it's imperative that voltage be stable and constant.

Resistors in Series and Parallel: Formula Derivation and Examples

© Eugene Brennan

Formulas for Resistors in Series and Parallel

Resistors are ubiquitous components in electronic circuitry both in industrial and domestic consumer products. Often, in circuit analysis, we need to work out the values when two or more resistors are combined. In this tutorial, we'll work out the formulas for resistors connected in series and parallel.

Learn How to Solder: A Complete Guide for Beginners

Image by permission Weller Tools

A Basic Skill When Building Electronic Circuits

Soldering is a fundamental skill essential to learn when building electronic circuits or fixing circuit boards.

What's the Difference Between Analogue and Digital?

© Eugene Brennan

Analogue vs. Digital

We often hear about analogue and digital in the context of communications, sound recording, cameras, TV, radio, and electronic devices. But what exactly is the difference, and is digital better than analogue? Why has digital replaced analogue in audio, digital imaging, and electronic communication?

Why Is Binary Used in Electronics and Computers?

Why is binary used in electronics? Geralt via Pixabay.com

Why Do Computers Use Binary?

The binary numbering system is the basis for the storage, transfer and manipulation of data in computer systems and digital electronic devices. This system uses base 2 rather than base 10, which is what we are familiar with for counting in everyday life.

How to Use a Multimeter to Measure Voltage, Current, and Resistance

© Eugene Brennan

What Is a Multimeter?

Multimeters are measurement instruments widely used by professionals in several fields including industrial maintenance and testing, research, appliance repair, and electrical installation. However, a digital multimeter (or DMM) is also an invaluable test instrument for home and DIY use.

What Are the Applications of Multimeters?

The instrument can be used for measuring voltage, current, and resistance and can check the following:

• Battery voltages in equipment
• Current through cables or components
• Vehicle electrics and electronics
• Continuity of cables and power cords
• Home appliances and electronic devices
• Fuses

Top 100 Cool Science Facts for Kids!

Photo courtesy Geralt on Pixabay. Text overlay © Eugene Brennan

Why is the sky blue? 

What is air made of? 

How many stars are there? 

World of wonder fun science facts that every child should know! This article covers space, nature, technology, engineering, elementary mathematica, chemistry, physics and biology.
Science is fascinating and tries to explain how everything in the world and outer space works. Science gives us the answers to questions like "What is electricity?" and "How does an aeroplane fly?" Read on and learn 100 more cool science facts! 

Airbus A320 Incident, Air Travel and Cosmic Radiation

Image created by Grok

Airlines worldwide have grounded their Airbus A320 fleets to carry out urgent software updates following an incident in October, when a JetBlue aircraft on a flight between the US and Mexico suddenly lost altitude after a pitch-down event, without any pilot input. According to a BBC report, "Around 6,000 A320 planes were thought to be affected," but many were able to fly again within hours after undergoing the software update. It's thought that the glitch on the JetBlue aircraft was caused by corruption of data in flight avionics computers, responsible for calculating elevation. A press release by Airbus on 28th November mentions "intense solar radiation" as being the possible cause of the recent event.

Cosmic radiation, consisting of high energy particles, mostly originates from the Sun, but also from the remnants of supernovae in our galaxy, the Milky Way, and other distant galaxies. It's more intense at higher altitudes where the thinner atmosphere has less of a shielding effect. The Earth's magnetic field also protects us from cosmic radiation, by steering particles safely into the poles, generating the spectacular phenomenon of the Northern and Southern Lights in the process. Cosmic rays can affect electronics, and there have been cases of glitches in satellites. According to a Scientific American article, "Extensive background radiation studies by IBM in the 1990s suggest that computers typically experience about one cosmic-ray-induced error per 256 megabytes of RAM per month."

This article from the EPA provides some further information on cosmic radiation and outlines its effects on passengers and crew on aircraft. 

Clock Drive Rotor

Wall-clock rotor (approximately 8 mm long). © Eugene Brennan

The mechanism (also called the movement) or working parts in a quartz battery clock is a bit simpler than in a traditional wind-up clock.

At the heart of the clock is a quartz oscillator, which generates a pulse every second. An oscillator is a device that does something regularly, like a pendulum that swings back and forth, a tuning fork vibrating, a string on a guitar or the air in an organ pipe. All these are mechanical oscillators, but there are also electronic oscillators.

An electronic oscillator generates a voltage signal that repeats itself at a set frequency. In the case of the oscillator in a clock, this runs at several thousand hertz or cycles per second. An electronic component called a quartz crystal sets the frequency of the oscillator to about 32,768 Hz with a high degree of accuracy. The frequency is divided down and reduced so that it eventually becomes 1Hz or 1 cycle per second. The output of the oscillator drives an electromagnet that acts on a tiny magnetic rotor, flipping it half a turn every second. The rotor has gear teeth that mesh with a train of other gear wheels and this eventually turns the hands of the clock.

Quartz clock mechanism. © Eugene Brennan

A closer look. © Eugene Brennan

Gadgets for Connecting to Old Hi-Fi Systems

Image courtesy Amazon.ie

This sort of gadget might be useful for those of you who have older hi-fi systems and want to stream music from your computer or mobile device. It's a Bluetooth receiver that has left and right, line-out outputs with RCA connectors for connecting to red and white line-in (sometimes called "Aux" ) connectors on audio equipment such as a hi-fi system. Cables are also available (or can be made up) to convert between line-out and DIN 41524, 5-pin connectors, sometimes used for auxiliary input on older equipment.

An alternative is to simply use a modern TV (which will have WIFi and Bluetooth connectivity) to generate the line-out signals for connecting to a hi-fi. Some modern TVs don't have red and white line-out connectors, just a digital optical output, however adaptors are available for converting this back to line-out for connecting to an older hi-fi system without optical input.

Hi-fis that only have phono inputs

My old Sony hi-fi from circa 1993 doesn't have twin line-in input connectors, just RCA phono connectors for the turntable. Although the connectors are physically the same as the RCA type used for line-in/line-out, phono inputs only accept low-level signals of a few millivolts (mV) generated by the cartridge on a turntable (the cartridge isn't powered and the signal isn't amplified). Apparently vinyl recordings use what's known as RIAA equalisation, low frequency sounds being attenuated during recording. The input pre-amp in a hi-fi or "stereo" that's connected to the phono input then does the reverse: cancelling the attenuation of low frequencies that was done during recording by boosting low frequencies on playback, resulting in an overall flat response. I won't explain why, but you can read more about it here.

Gadgets like this one are available that convert line level signals (from e.g. a TV) that are typically almost half a volt peak to the mV levels required by the turntable input. They also use a passive filter to attenuate low frequencies, simulating RIIAA equalisation.

Image courtesy Djbox.ie

I haven't personally used any of these converter adapters. Depending on what you pay for them, some are probably better quality than others and like like any intermediate system that converts and filters signals, noise and distortion will be added which degrades the final output. So sound quality won't likely be as good as when directly connecting line-out from a device to line-in of a hi-fi/amp.

CD vs Vinyl Debate

Generated on request by Bing image Creator.

In order to reproduce sound faithfully, the Nyquist-Shannon sampling theorem says that a sound can be perfectly reconstructed from its samples if the sampling rate is at least twice the highest frequency component of the signal. That's not the fundamental frequency of the sound, it's the highest frequency component of the signal when its spectrum is viewed in the frequency domain. The timbre or difference in tone colour between a pure tone and e.g. the sound from an organ, both with the same pitch and loudness, is that the organ sound has a fundamental frequency and higher harmonics (multiples of the fundamental frequency). The combination of, and amplitude of harmonics is one factor that makes the timbre of a musical note from a piano different from that of e.g. a flute or violin. The discussion in the forum at the link suggests that CD recordings should be better than analogue recordings on vinyl, considering that sampling is done at 44 kHz (twice the 22 kHz bandwidth allowed for audio signals). However there are other factors involved, and another forum member suggests that compression of the signal is involved when the pressing master is made from the original master, and production CDs suffer in sound quality due to this. Compression is necessary to reduce dynamic range (the difference between the loudness of loud and soft sounds) so that recordings can be listened to on earbuds rather than a hi-fi system, the latter having greater dynamic range capacity. This compression of dynamic range is distinct from the compression of the size of files to reduce the storage space required on media. That compression is variable and produces either lower quality/smaller file size or higher quality/larger file size recordings, typically in the MP3 (for audio) or MPEG (for video) file format. This is similar to the way bitmapped images are compressed into a JPEG image file. Unlike MP£ files, sound tracks on a normal CD aren't compressed and the data is in a raw format that can be read by the electronics.

A debate on the subject here. 

A Vintage Flyback Transformer

Teravolt at English Wikipedia, CC BY 3.0  via Wikimedia Commons.

These were used in TVs until cathode ray tubes (CRTs) were replaced by plasma and then LED displays. CRTs use an electron beam that traces out an image line by line on a glass screen, starting at the top left of the screen and working downwards. The path followed by the beam is just like how we read text on a page. A flyback transformer is used to produce a high voltage, in the order of tens of kilovolts, to accelerate the beam and make it strike a phosphor coating, the latter emitting light on impact. Only one point on the screen is illuminated at any one time, hence the bright spot at the centre of the screen when old TVs were powered down and the scanning coils were turned off. Persistence of vision and the 25 Hz scanning rate (50 Hz in total because of interlacing) give the impression that a complete image is displayed all at once.

USB Extender

Before USB, RS232 serial ports on computers had a range of up to 15 m, however USB is limited to a max cable length of 3 to 5 m, depending on data rate. If you can't use wireless and want to extend your USB connection up to 45 m, you can use one of these. The adapters are connected together using Cat 5 network cable. (I've used ordinary alarm cable, but it's supposed to be screened I think). It's only USB 1.1 standard, so not exactly for transferring lots of data fast, but could be useful for connecting to remote measuring instruments.

This product from RS extends USB up to 45 m.

How Do Spacecraft Get Their Power?

Rocket engines are used for propulsion on spacecraft, but the electronics has to be powered also. Frequently solar panels are used for generating electricity. But what happens if a space probe is so distant from the Sun that it's just a pinprick of light like any other star?

The Seebeck effect

If you heat the end of a piece of wire, it establishes a thermal gradient from the hot end to the cold end. This causes charge carriers (electrons or "holes") to move from one end of the wire to the other, resulting in a potential difference or voltage between the two ends of the wire. This is called the Seebeck effect. Devices that make use of this effect are called thermocouples and there's one in your oil or gas central heating boiler for measuring the temperature inside the burner chamber. A thermocouple is made of two wires of dissimilar materials twisted or bonded together at one end and can measure temperatures of over 1000 degrees C.

 

A thermocouple measuring circuit. Image courtesy Wtshymanski, CC BY-SA 3.0 via Wikimedia Commons

Thermopiles

Now as you may be aware, if you connect lots of batteries in series, e.g. AA cells end to end, the voltages add up. So for instance in a transistor radio, four AA, 1.5 V cells give 6 V for powering the radio. The electromotive force (EMF) or voltage generated by a single thermocouple is typically small, of the order of tens of microvolts per degree of temperature difference between its hot and cold end. If hundreds or thousands of thermocouples are connected together in series, they can generate useful voltages. This arrangement is called a thermopile. If all the junctions between the wires are made hot, and alternating junctions are kept cold, the device can generate electricity to power things. Thermopile powered radios, running on oil lamps, were used in remote areas of Russia in the past where electricity and batteries were unavailable.

 

Radioisotope thermoelectric generators (RTG, RITEG)

A radioisotope thermoelectric generator is a thermopile that uses a radioisotope source to heat the hot junctions of a thermopile while the other junctions are kept cool. The radioisotope source is typically materials such as uranium or plutonium. RTGs can generate hundreds of watts and were used in the Voyager 1 and Voyager 2 spacecraft, launched in 1977. The Perseverance Rover on Mars is powered by a 110 W RTG using Plutonium-238 as a heat source.

References

NASA. (n.d.). Mars 2020: Perseverance Rover - NASA Science. NASA. https://science.nasa.gov/mission/mars-2020-perseverance

Rowe, M. (2020, October 23). Thermocouples: Simple but misunderstood. EDN. https://www.edn.com/thermocouples-simple-but-misunderstood/ 

Thermo-electric generators. (n.d.). http://www.douglas-self.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm

 

 

 

Automatic Telephone Exchanges

A panel of stepping switches at a telephone exchange. Public domain image via Wikimedia Commons.

In Ireland, unlike the UK, we skipped having transistorised telephone exchanges and went straight from electromechanical (using relays, coils and motors) step-by-step or more modern crossbar systems to digital versions. When I was in the boy scouts in the 70s, I remember the whirring and clicking coming from the small telephone exchange building adjacent to our den (located in the tennis club building), as the exchange switched calls. Electrical pulses from a subscriber's telephone (known as pulse dialling, now replaced by tone dialling) caused a shaft on one of the mechanisms in the exchange to turn by a varying angle, the angle depending on the number of pulses. Each number from 0 to 9 on the dial of a telephone handset generated a different number of pulses. The shafts on the mechanisms in the exchange had an arm or arms attached, with electrical contacts on the end of the arm. As the arm swept around (usually limited to a half circle), it made contact with another set of stationary contacts, the process enabling a call to be connected to another number locally. Trunk calls to another "area code" would be sent to the exchange in Naas to be distributed to other local exchanges. From what I recall, in the early 70s, either Byrne's supermarket in Kilcullen or Athy still had a handset without a rotary dial, sitting near the meat counter at the back of the shop, presumably dating back to before the days of the automatic exchange.

 

This is an RTE report from 1989 about the changeover.

https://www.rte.ie/.../1045651-last-step-by-step.../

The Beginning of Radio Communication

Photo © Eugene Brennan

From one of the old books that belonged to my grandfather. A note in the appendix of a volume of the ICS reference library, 1905. If only they knew the developments that were to come in the future! In modern parlance, "the high-frequency transmission wave" is known as a carrier and the modification of the carrier by the superimposed wave is known as modulation. Sound waves having frequencies in the audible spectrum can't just be converted to an equivalent radio signal and transmitted. The frequency would be too low and for various technical reasons, including providing sufficient bandwidth for other channels broadcasting on and sharing the radio spectrum, and minimizing the size of antenna required, a technique called modulation is used. This is commonly either either amplitude modulation (AM) or frequency modulation (FM). The carrier is varied by a modulating signal derived from e.g. an amplified signal from a microphone, which changes the carrier's "size" (amplitude) or frequency. Originally, carriers were low, in the hundreds of kHz or somewhat lower. Carrier frequencies nowadays are vastly higher, typically 5 gigahertz (GHz) for WIFI and up to 108 MHz for normal radio broadcast programs on the FM band.

Photo © Eugene Brennan

 

How to Use USB Devices With Android Smartphones & Tablets: On-The-Go Cables

© Eugene Brennan

Why Do Computers Use Binary?

Public domain image by geralt on Pixabay