Form a signal from an array of bits

Question

I need to reproduce with a digital pin of an Arduino such a key in the form of a sequence of 1's and 0's, where a one takes 2 ms high and 2 ms low, and a zero takes 1 ms high and 1 ms low.

  int key = 0b101100001111;

void setup()
{
  pinMode(13, OUTPUT);
}

void loop()
{
  for (int n = 0; n < 12; n++)
  {
    if (bitRead(key, n) == 1) //execute if bit value == 1
    {
      sendSignal(2000);
    }

    else //execute if bit value == 0
    {
      sendSignal(1000);
    }
  }
}

void sendSignal(int duration)
{
  digitalWrite(13, HIGH);
  delayMicroseconds(duration);
  digitalWrite(13, LOW);
  delayMicroseconds(duration);
}

   

This sketch really works! I figured out what my problem is: I actually need a longer key (64 bits). I am using long type: long key = 0b1000011110001101111100011111001010110001101101111011011100110100; but long only allows 32 bits. What do you recommend to do? Maybe you need to arrange it as an array? I think you can make it easier somehow. thank you

Answer 1

You should make

byte key = 0b101100001111;

global, i.e. put it BEFORE the setup function and not within it.

Also, a byte only can contain 8 bits, you need 12, so make it an int (thanks to ocrdu, see comment below):

int key = 0b101100001111;

If you need more bits, you can use uint32_t or uint64_t, and count further than the current 12.

Now key is a local variable which is removed after exiting the setup function.

I'm not sure where 'key' comes from in:

switch (bitRead(key, n)) {

Do you get a compiler error, or did you ALSO define a global variable named key ? Anyway, if you make key global it will fix either way.

A few other remarks:

• Try to align your parenthesis, like the 3 }'s at the end, indent them properly, this makes your code much more readable
• Instead of the switch/case, you could use an if statement in this case, as the re are only (and always) two possible values (0 and 1):

Thus:

 if(bitRead(key, n) == 0)
 {
     ...
 } 
 else // 1
 {
     ...
 }

• Try also comments to write in English instead of Greek, you never know when your comments will be read by non Greek readers (like now).

• You can make the following fragment shorter and less duplicated:

Original:

digitalWrite(13, HIGH);
delayMicroseconds(1000);
digitalWrite(13, LOW);
delayMicroseconds(1000);

If you wrap this in a function:

void sendSignal(int duration)
{
    digitalWrite(13, HIGH);
    delayMicroseconds(duration);
    digitalWrite(13, LOW);
    delayMicroseconds(duration);
}

Then you can write a 1 by calling:

sendSignal(2000);

and a 0 by calling:

sendSignal(1000);

Answer 2

If you modify the code slightly, you can use an array of characters of any length, so need to worry about digital word length.

Here's a modified version of your program that does this.

Note that I also took the liberty of replacing the 'magic number' 13 with LED_PIN, and the 'magic number' 12 with KEY_LEN. I would suggest you do the same with your pulsewidth values - maybe something like PULSE_WIDTH_ONE_USEC and PULSE_WIDTH_ZERO_USEC? That way someone else (or you 3 months later) looking at your code can easily see what the values are intended to do

const int KEY_LEN = 62;
const char key[KEY_LEN] = { "10110110110101111001011010110100101011011100110110101101101100" };
const int LED_PIN = 13;

//int key = 0b101100001111;
void setup()
{
  Serial.begin(115200);
  pinMode(13, OUTPUT);
}

void loop()
{
  for (int n = 0; n < KEY_LEN; n++)
  {
    if (key[n]== '1') //execute if bit value == 1
    {
      Serial.print("1");
      sendSignal(200);
    }

    else if (key[n] == '0')//execute if bit value == 0
    {
      Serial.print("0");
      sendSignal(100);
    }
    else
    {
      Serial.print("x");
    }
  }
  Serial.println();
}

void sendSignal(int duration)
{
  digitalWrite(LED_PIN, HIGH);
  //delayMicroseconds(duration);
  delay(duration);
  digitalWrite(LED_PIN, LOW);
  //delayMicroseconds(duration);
  delay(duration);
}