wireless display

Question

I am attempting to build a keypad decoder, a wireless transmitter, a receiver and a 3inch LED display.

The decoder is working but I am having trouble determining what type data to transmit ie. character, byte or integer.

Since I will have to decode the data at the receiver, what would be the best type to use?

The initial code is;

#include <Keypad.h>

const byte ROWS = 4; // Four rows
const byte COLS = 3; // Three columns
// Define the Keymap
char keys[ROWS][COLS] = {
{'1','2','3'},
{'4','5','6'},
{'7','8','9'},
{'#','0','*'}
};

byte rowPins[ROWS] = { 9, 8, 7, 6 }; // keypad rows to Arduino pins

byte colPins[COLS] = { 12, 11, 10 }; //keypad columns to Arduino pins

// Create the Keypad
Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

#define ledpin 13 //define output pin to xmitter

void setup()
{

pinMode(ledpin,OUTPUT); //for testing
digitalWrite(ledpin, HIGH); //for testing
Serial.begin(9600);
}

void loop()
{
   //for (int(c); c <2; c++); I would like to accumulate three bytes and transmit together if possible
   char key = kpd.getKey();
if(key) // Check for a valid key.
{
    switch (key)
    {
      case '#':     //Clear data for re-entry
        digitalWrite(ledpin, HIGH); // for testing
        break;                      // for testing
      case '*':     // Display data on receiver
        digitalWrite(ledpin, LOW); // for testing
        break;                      // for testing

      default:    //send data to xmitter     not working! It only sends to! computer display.
        Serial.println(key);      // for testing

}
}
}

All help would be greatly appreciated. This is a project for our church.

Thanks

Bill

shabaz · Answer

Hi Bill,

Did the '#' and '*' do what they were intended to do (turn the LED on and off)?

If so, then it's just the 'default' area of the switch statement that needs investigation.

By the way, there should be a statement 'break;' after the Serial.println line (not sure if it compiles

without that, but it's good practise to put it.

Also, the println thing appears to accept any data type. When you have a single char, it is internally

represented as a single byte, not as a string. So, as an example, if you press the number 3, since your code represents it

as '3', the compiler interprets that as an ASCII character which needs to be translated into a byte.

ASCII char '3' is equivalent to the decimal number 51 (I just remember that ASCII char '0' is decimal 48

and then you can add as appropriate, so 48+3=51).

Another way to mentally remember it is that ASCII char '0' is hexadecimal 0x30. So, ASCII '3' would be

hexadecimal 0x33.

Anyway the point is, that according to this page it appears that if you use println with an integer (and I'm

guessing it will have similar behaviour with a single byte which is what a 'char' data type is), then it will

send to the serial port a "ASCII-encoded decimal". This means that if the byte is 51, then it will send four

characters over the serial port: ASCII '5', ASCII '1' and ASCII CR and ASCII LF (carriage return and line feed).

I don't know what your receive function looks like, but maybe you intend to send a single byte, in which case

println can be replaced with 'write' as shown here.

serial.write(key) will then send the single byte of value 51 using the same example.

If you wanted to send the number 3 instead of the number 51, then you could do: serial.write(key-'0');

which the compiler will translate to serial.write(key-48).

I hope this helps. I don't know arduino, so I may be wrong on some points above.

Robert Peter Oakes · Answer

If you look at lesson 2 of my tutorials, it deals with reading a character at a time from the serial port into a buffer, a later lesson deals with doing the same from the Ethernet port. The serial port version can easily be adapted to read from the keyboard instead, it then goes on to deal with how to make decisions based on what is read

you can find it here Fast Track to Arduino Programming

the key part in this lesson in your case is replacing the serial.read() with your getkey() and also reducing the buffer size to 3 which you state is your requirements.

You may want to start from lesson 0 though if your not familiar with programming the arduino

If this is still to complicated right now, let me know and I can simplify the relevant parts of the program for you

Regards

peter