Arduino Software

This is a continuation of the Arduino for Pilots post. This post will be an introduction to writing software for the Arduino, assuming you know nothing about programming anything. If you know another language, this will be helpful to apply those principals to the Arduino. A great deal of the Arduino code is already written, in the forms of libraries, so most programming will only be using these libraries to do the things you need.

The Arduino web site has the list of libraries available. The language reference page is a fairly complete list of commands built in to the Arduino. Understanding some of the concepts may not be obvious, to someone who hasn't programmed anything before.

The blink sketch used many of the basic things that are needed to get started programming. Have a look at it again:

/*
  Blink
  Turns on an LED on for one second, then off for one second, repeatedly.
 
  This example code is in the public domain.
 */
 
// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 13;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);     
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second
}

The characters "/*" begin a comment block, and "*/" end that comment block. All text between the "/*" and the "*/" are considered comments. Any new lines and punctuation are allowed. Comments are used in programming to add information for the person reading the code at a later date. The computer doesn't use or look at these values at all. They can be in Dutch, Italian or English, what ever is needed to make things easier for the person looking at the code.

Sometimes a programmer while writing code just wants a quick note about a particular line of code. The lines of code start on the far left, and end at the right, and are only one line long. If a line contains the characters "//" that is the start of a line comment, and end with the end of the line. These are comments for the readers of the code, and not the computer.

The first line of real program is the initial variable declaration. This line is a statement. Program statements start after a comment block, or after another statement. Statements must end with a semi-colon ";".:

int led = 13;

A variable has a type and in this case is an integer specified by the "int" characters. Integers are whole numbers, no fractions or decimal places. For the Arduino, they have a range of -32768 to 32767. For many applications integers are adequate, but if more range is needed, and no negative value are useful, specifying an "unsigned int" will allow a range of 0 to 65535. There are other variable types, and we will get into them more in a bit.

The variable has a name. For this application the name is "led". It doesn't matter what the name is, the computer will only look for this name and work with the value with that name. We can give variables meaningful names, or we can name them a, b, or c, but meaningful names will help maintain the program that is written. Names in programs must start with a letter, and may not contain any spaces or most symbols. After the first letter, there may be numbers and underscores.

The variable can be initialized when declared. For this program, the variable is initialized with 13. This variable will be used to tell the computer what pin this program will control the LED light with. The program didn't need to use a variable for this program, we could have used 13 everywhere "led" is used, but if someday the LED light was moved to another pin,  all the 13's would have to be changed to the new value. Using a variable like this, if the LED was moved to another pin, only the variable "led" needs an new initial value and the program is ready to go.

The last character in the statement is the semi-colon notifying the computer that this statement is done. The carriage return/new line doesn't mean anything to the computer. The next statement could start right after the semi-colon. Using white space (indentation, and new lines) makes the program more readable. 

Since the "led" variable is declared outside any functions, it is considered a global variable. A global variable is one that can be used inside any function, in this sketch. There are function private variables that are only visible inside the functions where they are declared. 

The next line of real program is the function declaration:

   void setup() {

This is an entry point for every program. The Arduino always runs some code. It is sort of like an operating system, allowing uploading and running programs. When a new program is started (after upload or reset), the first thing the Arduino loader runs is call the function "setup".

There can be any number of functions in a program. A function is declared with a return value, in this case "void" indicating there is no return value. Some functions may do some calculation or lookup some information and return a value. Functions can return integers and other values as well.

The next part of the function declaration is the function name. There are two functions all Arduino programs must have, "setup" and "loop". If there is a need for a calculate cubic feet function, a function can be created that has the name "CalculateCubicFeet". The names need to be spelled and capitalized properly. A function named "setup" is different than a function named "Setup". Having multiple functions with the same name, just different capitalization's can make reading the code more difficult.

A subtle part of this function declaration is the arguments section. For this function there is nothing being passed to it, so there is an empty pair of parenthesis "()". If there was a function CalculateCubicFeet, to make is flexible, there may be three arguments passed to it like:

    int CalculateCubicFeet(int x, int y, int z)

where the three values passed to the function are x,y and z, each and integer. Arguments passed to the function are only visible inside that function. The argument x in CalculateCubicFeet cannot be used in the setup function.

The last bit of the setup function declaration is the "{". The "{" is the start of commands that will be done when this function is called. The other "}" is the last line of the function, and means that is the end of the function. This line doesn't have to be on the same line as the name and the open and close parenthesis but usually is.

Inside the setup function, since it is past the "{" is a library function call "pinMode". Pin mode takes two arguments, the pin to set the mode of and the direction the pin will be when the program starts. The Arduino language reference page has a link to the function "pinMode". The language reference page will describe the function in detail, and offer some examples. This is the same for all built in functions.

There are some built in constants and variables in the Arduino library. Constants are named values that don't change. Variables are named values that may change during the execution of the program. One of the constants that the "pinMode" function uses is "OUTPUT".  Writing a program  using values other than the constants defined is discouraged, since the program may stop working when used on another computer.

The setup function does one thing, it sets pin 13 (led) to be an output pin. Instead of specifying 13, the program uses the variable "led" which is set to the value 13. Being an output pin means the values are set on those pins. If a switch were connected to pin 5, and there was a desire to read that pin, then using the pinMode function, pin 5 could be set as input:

    pinMode(5,INPUT)

Once everything in the setup function is complete, the program will jump back and let the Arduino system have control again. The Arduino system will do whatever housekeeping it needs to and then immediately call the "loop" function.

The loop function is declared almost identically to the setup function. There are no return variables, so the void type is specified. The name happens to be "loop", and that is necessary so the Arduino system knows where to go next. There are no arguments to the function, so there are empty parentheses. The real work starts after the "{".

The first library function call is the "digitalWrite" function call. The digitalWrite function will set the value on one of the pins. There are two arguments to digitalWrite, the pin, and the value. All the digital pins only care about two values, the constants "HIGH" and "LOW".  High means that when measured against the ground pin, the value on the pin specified will be about 3 volts. Low means 0 volts when compared to the ground pin.

For this program, pin 13 will be set to the HIGH value to turn the light on. Again, instead of specifying 13, the program uses the variable "led" which contains the value 13.

The next library function call is "delay". The delay function takes one argument, the amount of time to wait in milliseconds. The current program just stops for that much time. The Arduino system is still doing it's thing, but the program written waits that many milliseconds. A programmer can create a variable so the 1000 would have a name, something line "oneSecond" would be good, but it isn't necessary. 

The next two lines are like the first two in this function. Calling the library functions digitalWrite and delay are used to turn the LED off and to wait before exiting this function.

Once the function hits the "}", it will return control to the Arduino system. The Arduino system will take care of any housekeeping it needs, then call the loop function again. This process will repeat until the system is powered off.

These introduction posts are long, and I hope the help make the Arduino system understandable. In subsequent posts, there will be more meat regarding doing airplane stuff with and Arduino, but without this basic understanding, any other posts may not be useful. Post any questions or subject area anyone may need help with, and I will try to get more help out there.

Arduino For Pilots

I am a technology geek. If it has a computer, I at least look at it, and maybe buy one to play with. The Arduino first became available almost 10 years ago as a simple way for hobbyists to get started with microcontrollers. I started playing with AVR micro-controllers, probably 10 years ago, because they were already simple. The Arduino platform makes it easy to do things with quickly.

I started this blog assuming anyone reading it would know all about the Arduino, and be ready to follow me right away. Then I started reading about aircraft homebuilders building relay trays, and all kinds of PLC and silly other things, and it occurred to me, not everyone knows about micro-controllers and the simplicity they can provide.

The Arduino is a series of micro-controllers that are organized in a simple consistent design. There are some that are smaller than the normal design, but most of the popular boards support the basic pinout. The most popular boards are the UNO, and the Mega. All the boards are programmed the same way using the Arduino Integrated Development Environment (IDE) over a USB connection.

The smaller boards like the Uno have about 16 general purpose IO pins, 6 Analog input pins, a serial port (SPI), and various power pins. The organization of these pins is consistent for most boards. The Uno, Diecimila, Duemilanove and the Leanardo are basically the same.

The larger boards like the Mega, have over 50 IO pins, 16 Analog input pins, the same serial interface (SPI) and power pins as the smaller boards. The layout of the board starts with the same pin organization as the smaller boards, but since the Mega board is longer the extra pins are out past the edge of the smaller boards.

Relying on this consistent pin layout has allowed expansion boards to be built. These expansion boards are known as "shields". Most of the shields add specific functionality to the basic Arduino. Shields include servo and motor controllers, GPS, ethernet, WiFi, and Bluetooth. I think there are over 100 different shields for the Arduino family of controllers as of now. 

Many of the shields allow other shields to plug into them. Having a whole stack of shields isn't uncommon. A project may include an Arduino processor board as the base, a special IO shield in the middle and either a bluetooth or WiFi shield plugged into that. The only limit to the number of shields is power available, and mechanical constraints.

Using an Arduino can be done with only the board and a USB cable. All the programming will be done using the USB cable, and power on the USB can supply the board. Most computers are limited on the amount of power supplied over the USB port, so there is a second coax power connector available to power the Arduino with more if needed for the various shields. The Arduino can run off a phone charger USB adapter once a program is loaded.

Many retail outlets are selling the Arduino processor boards and shields. Radio Shack, Micro Center and Fry's all have Arduino boards in most of their stores. Many online electronic suppliers also have Arduino boards and shields, and their selection can be more extensive. The UNO boards can be bought for as little as $10 retail. Buying a starter kit is a good idea if you have never worked extensively with electronics, since this will come with wires, LED lights, switches and various other components making connecting an Arduino to an airplane easier.  Shop around, see what you like.

The Arduino IDE is available from the Arduino web site for free. There is a version of the IDE available for most computers including: Windows, Mac, and Linux. It is an open source project, if you have another platform, you may need to get the source and compile it for your platform.

Installing the IDE is occasionally a challenge on Windows. The FTDI USB driver isn't included with Windows, so you may need to download the driver for your OS. Mac and Linux usually work without any challenges. There is plenty of help installing using the Arduino.cc forums. If you see an error, just enter that error message in the search bar for the forums, and it will probably take you to the solution.

Programming an Arduino is very simple. The IDE comes with many examples, that will run on most boards. The programs written for the Arduino in the IDE are called "sketches". The simplest example sketch is a blinking light. The blinking light sketch will blink the light on the Arduino board itself.

The sketches included are source code. To select the blink sketch, open the IDE and select File->Examples->Basics->Blink. A new window should open, showing the source code for the blink example. The text between "/*" and "*/" are comments, as is the text after "//". If you have ever worked with C or Java this syntax should be very familiar. Comments are only there for the people reading the code, the computer doesn't use that information at all.

/*
  Blink
  Turns on an LED on for one second, then off for one second, repeatedly.
 
  This example code is in the public domain.
 */
 
// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 13;

// the setup routine runs once when you press reset:
void setup() {                
  // initialize the digital pin as an output.
  pinMode(led, OUTPUT);     
}

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second
}

There are two kinds of syntax after the inital comments, function definitions and variable declarations. The line:

   int led = 13;

is a variable declaration, saying some name "led" is declared as 13, at least for now. It is at the top of the program making it a global variable. Global variables can be used anywhere in the program. In this case, when the word "led" shows up, the value 13 will replace it.

The two lines:
  void setup()
  void loop()

are function definitions. Arduino will call these two functions in every program. The setup() function is used at the begining of a program to make sure the board is set the way you want. The loop function is called the rest of the program run time, and does all the real work.

For the blink program, the setup() function is used to set the IO pin "led" (13) to be output using the pinMode() function call. Output means the computer will send messages to that pin. Input would be used for reading messages from that pin.

For the blink program, the loop() function is what does the actual blinking. digitalWrite() is a function that is part of the standard library, allowing data to be set on specific output pins. The first thing done is to digital write to the "led" (13) pin to be high, or to send 5V on that pin. delay() another function in the standard library that tells the computer to wait here for some milliseconds, in this case 1000 milliseconds, or one second. The next digital write will set the "led" (13) pin to be 0 volts or off and then the computer will delay another second and exit the loop function. The built in Arduino manager will call the loop function as soon as this loop function finishes. Each of the lines has a "//" followed by an explaination comment as to what that line does, and it helps the people reading the source code, but is only optional.

To send this program to your Arduino, the IDE will need to be set up.  Under Tools select Board and the board you are trying to program. If you have an Uno, select Tools->Board->Arduino UNO from the boards menu. Then you need to set the port. The port will be the place the board is connected to as your computer sees it. For Windows it may be COM6 or something other than COM1 or COM2. For Linux, it will probably be /dev/ttyUSB2 or something, use dmesg to see what the computer named the port when the board was plugged in. The Adruino web site has all the information in the getting started page.

Once the board and the port are set, the sketch can be uploaded to the board.  Press the forward arrow button or File->Upload or ctrl+U, to upload the code to the Arduino. At the bottom of the IDE window, the current status will be displayed. First the source code will need to be converted to AVR binary code through the process of compilation, then the resulting binary code will be sent through the serial port to the Arduino board, and the process will start running.

If everything has gone well, the LED light on the board will start blinking one second on, one second off. The code is "burned" in to the computers memory. When the Arduino is unplugged, the code is still there, but the processor will stop running. Plugging the Arduino back in, the blinking will start automatically.

To change the pattern of the blink, in the IDE, change some of the values. To make the light appear to flash, change the delay() value after the on digitalWrite() call. A very quick on, could be something like a tenth of a second (100ms). Delete one of the zeros, and upload your code. Notice how the light just blinks briefly, and stays off for the full second still. Other settings can be used to give other patterns.

I am going to end this article now. I think there is a lot to chew on, and hopefully I have wet your appetite to try new things related to controlling things using a microcontroller. Next time I will add inputs and additional outputs, including motors, switches and lights.

What else do you want to know?

Data Comm Tools We Need

I spent the last week on a business trip, and managed to go most of the week without WiFi. The airplane I flew on didn't have WiFi, and while in the car I didn't have it either. I was staying at a 5 star hotel for 4 nights, and had only marginal coverage, at $13 a night. I ended up using my mobile hot spot on my phone and burned through over half my monthly allotment LTE internet in 4 days. I learned how much I rely on data connections.

Several years ago, probably 1998 or so, my wife and I were at Oshkosh, and walked by the Iridium booth. The Iridium sales person offered us a free phone call to see how great their products are, and maybe we could use them in our airplane. This was before my wife or I had a cell phone, and we wanted to check in on the kids. After three or 4 failures, we never got to talk to the kids, and we walked away unimpressed.

About a week ago, the Airplane Geeks had the president of Iridium on the show and allowed him to hawk his products.He presented a new product that sounds like something pilots can use in the plane, and maybe other times as well. The Iridium Go looks to be the perfect implementation of the Iridium network for us.

The Iridium Go is a WiFi hotspot that will work anywhere in the world, at almost any altitude. This is the opportunity to make a tablet and phone work anywhere all the time. When in the air, the tablet can get all the data updates desired, along with making VOIP phone calls on the phone. The Go also has tracking and other useful features built in.

I know FIS-B and TIS-B should have much of the datalink covered, there are some things it won't have covered. Items like downloading whole graphical charts while in the air, or additional weather information will not be available over FIS-B.  TIS-B and FIS-B aren't available outside the CONUS either, operations there will benefit from additional datalinks.

Airlines have the ability to use Iridium datalink today, and the ICAO flight plan has a capability letter reserved for CPDLC using Iridium (J7 CPDLC FANS 1/A SATCOM (Iridium)) in Item 10. To put Iridium radios in commercial aircraft is a very expensive aftermarket event. Using the Iridium Go for non-safety of flight purposes is a much smaller cost (More than an order of magnitude!).

The price is around $600 for the GO, and while that sounds high, consider the cost of a typical smart phone is in a similar ballpark (off contract). One might guess if these devices become quite popular, the price may come down.

For tooling around in your Taylorcraft, this might be overkill, but I could see it becoming almost an expected item on a Citation, or King Air. People rely on data communications a bit more in the 21st century.

(Iridium hasn't talked to me at all, I saw this and thought this is  great product!)

Stuff To Learn

I knew the different Arduino boards are all a little different, but I didn't realize the Arduino Mega 256 was really different. My other Arduino Mega is only a 128. The Mega 128 and most of the other Arduino boards use the FTDI USB interface. The Mega 256 uses a ATMega8U2 chip, like the UNO. The boards sure look the same

Now I am using Linux to do development, so the serial port ends up being called /dev/ttyACM0 instead of some /dev/ttyUSB0. No big deal really, it is just I was surprised there were more differences than I expected. The Arduino on Linux page has many helps to get things working.

I took the basic sketch, blink and modified the loop to be sure I knew it was my code running on it.

// the loop routine runs over and over again forever:
void loop() {
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(100);               // wait for a tenth of a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(100);               // wait for a tenth of a second
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(100);               // wait for a tenth of a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(100);               // wait for a tenth of a second
  
  digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);               // wait for a second
}

Now I want to get things working with the display. I bought a LCD touch screen for this. The screen looks familiar, almost identical to the Sharp Zaurus screen. (we can talk all we want about iPhone/Android but the reality was there were smart devices running a *nix flavor waiting for a phone a long time before either were invented! Zaurus was the first one I had, the Nokia 770 was the second, wifi enabled internet connected personal mobile devices).

There is a thread on the Arduino forums about this device, including locations of the libraries. I am going to build a minimal graphics library so I can build a display of the basics before I start using the bluetooth connection to the Android. 

Doing The Annual Inspection

The weather is getting nice, and I am wanting to work on the plane again. It should be put in condition to fly, and that requires an annual condition inspection. My airplane, being an experimental, and built by me mostly, I have the ability to do my own conditional inspection and sign it off. It hasn't flown for almost 3 years, so I haven't done a complete conditional inspection for some of those years. This one is going to be thorough, I am in no hurry to actually fly.

I've got everything opened up. There are items that need repair (IE drip rail in the front that I broke while storing a box inside the plane), and other things that need a good looking at. I am changing the oil, and sent a sample off to a lab for analysis, to be sure the last couple years of dis-use hasn't done significant damage to the engine. The lab will test the oil for elevated levels of metals that may be early signs of engine damage.

I am looking at the firewall extensively for the engine monitor, and where to attach the monitoring computer.  Most of the smaller wires between the engine and the firewall are for sensors. The wires around the oil filter are oil temperature and pressure sensors. The silvery wires are EGT/CHT thermocouple wires. Under the engine are the fuel pressure wires.  There are the ammeter wires on either side of the shunt (that is a bit of old fashioned technology).

In the annual inspection, I found the ammeter light is burned out. This light is only needed for night flying, since I can see the instruments during the day. Each engine instrument has it's own light bulb, so I am 1/6th of the way through needing to replace them all. It'll be good to replace all the engine instruments with a smart box to monitor all this, as well as display current state.

I've started on the bluetooth code. That is a bigger challenge than I thought, mostly because the Android emulator doesn't support bluetooth. I need to keep my phone plugged in and use that for the tester. It isn't bad, but the phone has lots going on, so the log files scroll fast (and this is my only phone right now.

Soon the annual will be done, and hopefully about that time, I'll be ready to put my arduino in the plane, and start testing some of this. In the mean time, I've ordered another arduino, a mega 256. It seemed I ordered that the same day the arduino zero came out. Why am I messing with 8 bit micros when 32 bitters are about the same price? I don't know, comfort maybe, or maybe it is all I need, the 32bits may not get me anything. (The zero only has the same number of IO pins as an uno, so there isn't a big win yet, some day there may be a mega zero, until then, I'll keep using the mega).

More Engine Monitor Updates

This will be kind of a quick post, but the gist of it is, I've been busy. In between getting a new version of my other app out, and explaining the technology behind these gauges on my other blog, I haven't been watching a lot of TV or hanging out in bars.

The new gauges have options that work, and the interface and abstract implementation make these very flexible. Looking at all the gauges, they mostly have the same call, the size differences are sort of hard coded.

In the picture above, you will see round and bar gauges, mostly the same as before. The new changes are the round gauges can go in either direction, be 270 degree, or 180 degree (any sweep angle should work) There is one CircleGauge class that actually draws them all! The CircleGauge class is extended by things like the Ammeter class, or the Volts Meter class.

The gauges have options for clockwise/counter-clockwise, ticks, and various color options (I haven't been setting the color options, these are the  default values. The gauges can have a rotated start angle, and display the title and value in the center of the gauge.

The gauges all get their values from an EngineValues class, that can be set at any time. The next steps will be to put in the bluetooth reading code that will allow me to connect the Arduino to the engine and start measuring values.

What-cha think? Am I heading in the right direction?

Engine Monitor Progress

I am gaining a bit of experience in Android development. Some things I did in that last app are helping, while I need to learn more to make this work. One thing I have clearly learned, the drawing canvas can be made into tiles. This is important, since if the app is to display both in portrait and landscape, it will be much easier to move individual gauges around than trying to use different offsets depending on orientation.

rough example

The other thing I learned, these gauges can have a million options! I may need about half that many before I am done as well. Should the round gauge turn clock wise or counter clock wise? Should the green arc be thick or thin, should the ticks be shown or not. Of course I can add all those options, and I still need to add more.

I've built the individual instruments using normal Object Oriented (OO) concepts. I could just as easily substituted the tachometer as a bar graph as a round gauge. I also have the ability to build an new type that can be a line graph or something, and only have to change the code a little. I can change the individual gauges, and probably not have to change the implementers code as well.

The OO concept allows a great deal of flexibility. Everything is abstracted away, such that the value of the fuel pressure will not really care what color the pointer is, or that the gauge is round or some other shape. Where it is placed on the screen is equally irrelevant, and allows the user to change the layout of the screen to suit their needs, and present the most important information in the most prominent position.

I am making progress, I just keep getting bogged down in implementation details, that can probably wait. Some of you are looking at this and saying, "it isn't very good". Fine, tell me what other things I should change to make it better looking. I've already considered OpenGL 3D looking instruments, and non-linear scales, red lines at limits, and many other things. The app will include audio and visual alerts depending on settings.

For now, I have all the instruments I need for my airplane on the screen. I have provisions in the code for 6 and 8 cylinder EGT/CHT values, as well as manifold pressure, and temperature. I want the screen layout to be customizable by the user, so they can pick the instruments they want, and where they are on the display.  


 Thanks for your feedback so far.