We will see how Morse code can be used for communication from a tiny IQRF (see reference ) TR-52BA board that contains an LED and a PIC16F886 microprocessor. The program is written in C and compiled by free CC5X C Compiler for the PICmicro Devices version 3.4 from B. Knudsen Data .
The Morse code was developed 176 years ago by Samuel F. B. Morse and Alfred Veil to transfer textual information as a series of on/off tones, lights or clicks that can be directly understood by a skilled listener or observer . We will use the Morse code to broadcast information about the current status of the TR-52BA  board and application installed.
IQRF platform and the TR-52 transceiver
IQRF  is a complete modular platform for wireless connectivity based on smart transceivers that are affordable and very easy to use. The RF transceiver  is radio transmitter and receiver built into one. We do not really care about the radio connectivity in this project. The IQRF transceiver is equipped with a built-in PIC microcontroller that we want to program. We will use TR-52BA transceiver that is equipped with PIC 16F688 microcontroller. Our program should run well on any IQRF smart transceiver and principles shown here are applicable to a wide range of PIC microcontrollers.
The Morse code consists of dots (short beeps called dits) and dashes (longer beeps called dahs). The dash is
three times longer than the dot and there is a pause lasting the same time as one dot between beeps in the character and a pause lasting as one dash between characters. The pause between words should last as 7 dots. The dot for faster transmissions known as CODEX should last 50ms, for slower transmissions known as PARIS 60ms. The transceiver timer goes in 10ms intervals. We will define
two macros to conveniently handle timing:
#define dot 6
#define dash 18
For convenience and better readability of the code we will wrap time handling into
void pause( uns8 delay )
delay *= dot;
waitDelay( delay );
The function receives parameter delay with required delay length in dots. Therefore we multiply it by the dot macro to get the value in multiples of 10 milliseconds and we send that value to the
Operating System function
waitDelay(). See  for the complete list of all goodies the operating system provides.
BTW: we are modifying the incoming parameter inside of the procedure. This is benign, the C function arguments are sent by value, not by reference.
_LEDG = 1;
_LEDG = 0;
The predefined address
_LEDG works like a binary variable that is associated with the leg of the PIC that is soldered to the green LED on the transceiver. Setting the value to 1 will light up the green LED. Settling the
_LEDG to 0 will switch the light off. There is also a red LED on the RT-52BA. We can control it the same way using the
How did I know to use the
_LEDG? The IQRF provides a nice development environment as a free download from . Description of predefined memory locations is in the
Note also that we included a pause lasting one dot length after the beep to separate the beep from the next one. The
dah() function is very similar to
dit(), the only difference is that the beep is longer.
_LEDG = 1;
_LEDG = 0;
Morse code table encoding
There is not much RAM to waste on tiny PIC chips. Therefore, we need to plan to store the Morse code in the memory efficiently. The Morse code being made of dots and dashes only naturally suggests binary storage with 1 for a dash and 0 for a dot. For example the letter C (dah-di-dah-dit) would be encoded as 1010 or 0xA in hexadecimal. Fortunately, the Knudsen’s C is extended to support binary literals that you can write as bin(xxxxxx) or 0bxxxxxx where the x is either 0 or 1. The syntax allows for a “.” (period) symbols to separate individual bits for readability purposes.
The length of the Morse code for individual characters varies. Since the length is no more than 5 beeps, there are 3 bits left to store the length of the code in the same byte where we store the code. We decided to store the length in rightmost bits. For example the letter C would be 0b0.1010.100. The last 3 digits 100 (decimal value 4) tell us that the code for C has 4 beeps. The central part of the byte “1010” is the code and the extra leftmost 0 is one bit we did not use.
Storing the whole code in an array sorted alphabetically is very natural and helps in picking the code for a given character.
static uns8 m;
encoded_character = m[ character_to_encode – ‘A’];
We take an advantage of knowing that all capital letters are ANSI coded continuously and alphabetically. We can use the same trick for lower case letters.
Once the code for the character was found, it can be broadcasted it by sending it to the following function:
void key(uns8 a)
uns8 n = a & 7;
for( n = n + 2; n > 2; n--)
uns8 mask = ( 1 << n );
if( a & mask )
The number of beeps in the character is extracted from the code byte by masking. The number 7 is 0b000111 in binary, a bitwise AND operation with it removes all the other 1s form the byte. We will store the value in the variable n:
uns8 n = a & 7;
Then we loop through bits in the code byte starting from the position n+2 (bits are indexed from the right, starting with 0) and continuing down up to the index 3. We do not want to broadcast the last 3 bits that we used to store and get the code length.
To pick the indexed bit from the code byte masking can be used again. We create the mask by shifting the value 1 to the left so it is in the position of the indexed bit.
uns8 mask = ( 1 << n );
Then, if the result of masking is 1 we broadcast dash, otherwise it is dot.
dah() functions are written to insert a pause lasting one dot after every beep, we need to add a pause with two dots length to finish the character.
Other notable parts of the code
To obtain the information about the status of the user application we call the operating system function
appInfo(). The function will fill-in 32 bytes of the bufferINFO memory with the information in ANSI text format. We loop through that buffer and broadcast the text stored there.
PIC microprocessors are equipped with a watchdog timer as a protection against deadlocks . If the program is not informing the system about being active for a long time (in the microelectronics world 4 seconds do look like a long time) the watchdog resets the processor. Since we intentionally delay the program execution, we need to let the watchdog know (kick the dog) from time to time. We do it before broadcasting each character by call to the operating system function
Programming the transceiver
To bring all the parts together we use code template file named template.c that was downloaded with the IQRF IDE . The complete code is attached. Now we will use IQRF TR host USB module CK-USB-04 that connects to PC via USB cable.
- Insert the TR-52BA into a SIM card connector on the host module.
- Start the IQRF development environment iqrf_ide.exe.
- Select the Programming tab, click Open File, browse to our program and click Open.
- Click Compile and check the compilation report for errors. There should be none.
- Click Enter PROG Mode and click Upload. After a second the green LED starts telling you in Morse the application status of the transceiver.
Our program is now compiled and stored in the transceiver memory. We can remove the TR-52BA from the base USB module and it should start blinking the Morse code every time we reset the processor or reconnect the power. We still want to avoid soldering so we put the programmed transceiver into another IQRF base module DK-EVAL-04 that has built-in accumulator. Now we can walk to friends and impress them by the tiny light blinking the Morse code.
Our program works with upper/lower case English alphabet and space characters only. Any other character is ignored. One day we might extend the program to cover the complete Morse code.
 IQRF wireless platform http://IQRF.ORG
 CC5X C Compiler for the PICmicro Devices version 3.4 from B. Knudsen Data http://www.bknd.com/cc5x/
 Wikipedia Morse code article (February 2012 version) http://en.wikipedia.org/wiki/Morse_code
 Wikipedia PIC microcontroller article (February 2012 version) http://en.wikipedia.org/wiki/PIC_microcontroller
 IQRF distribution http://IQRF.us
 IQRF OS 3.0 Functionality http://iqrf.us/functions.html
 IQRF downloads include IQRF IDE development environment with sample code and a new project template http://iqrf.com/weben/index.php?sekce=support&id=download
 Wikipedia Watchdog timer (February 2012 version) http://en.wikipedia.org/wiki/Watchdog_timer