Receive binary data into a variable

Projects Programming
1

Hey all, I'm very new to Arduino and need some help with a project.

I want to receive 8 bits of binary data on the hardware serial port (9600n2), look and the first 4 bits (it's an ID) to see if it's addressed to us, and if it is then compare the last 4 bits to some known's to decide what the message was telling us to do.

I can handle the latter, but not sure how to wait for the serial port to get 8 bits in the buffer before doing something, then how to store the first 4 in a ID variable and the next 4 in another variable.

Please any help to get me on the right track would be appreciated.

Thanks :slight_smile:
-Matt

2

Hello and welcome :slight_smile:

You could wait for 8 separate bits, or you could send a single byte that you then parse in your sketch :slight_smile:

Example:

byte binary_data = 0b11000101;

byte ID_variable = (binary_data & 0xF0) >> 4; //will be equal to 0b1100
byte another_var =  binary_data & 0x0F;       //will be equal to 0b0101
3

The arduino handles serial communications for you - it delivers the data a byte at a time, so there is no need to worry about waiting for individual bits. You use serial.available to find out if any data has arrived, and if so, serial.read to get it.

4

Thanks for the reply's

Still a bit lost (no pun intended).

Perhaps it's better if I tell you what is happening.
In total there are 10 ID's:
0000
0001
0010
0011
0100
1000
1001
1010
1011
1100

Then the next 4 bits are a binary number 0 through 9 (9=1001 and so forth)

I need the arduino to listen for it's own ID and then store the ascii number into a variable.
After that I'm driving a 7segment display directly from the arduino.

It's kinda like mimicking a 7seg latch driver.

I just don't understand how to get from the binary serial to the point that I have a ascii value stored in a variable.

5

What is sending 8 bits to the Arduino? You with the Serial monitor, or a sensor/device?

mjwillia:
I need the arduino to listen for it's own ID

So you have 10 Arduinos, each with it's own ID?

6

Yes, Correct

They are scattered all over a building connected by RS485 (I convert back to rs232 before giving it to the arduino).
The binary data stream originates from a propriety system I can't change.

7 
if (Serial.available ()) {
  int candidate = Serial.read ();
  if ((candidate & 0xF0) == myAddress) {
    char ascii = '0' + (candidate & 0x0f);    // edit: sorry, forgot the masking here.
  }
}
8

Ok then you have to wait receiving 8 bytes, that you then convert in a single byte :slight_smile:

Something like this (maybe):

void loop()
{
  if ( Serial.available() == 8 )
  {
    byte bytes[8];
    for ( uint8_t i = 0; i < 8; i++ )
      bytes[i] = Serial.read();

    byte result = 0;
    for ( uint8_t i = 0; i < 8; i++ )
      result += bytes[7-i] << i;

    byte ID = (result & 0xF0) >> 4;
    if ( ID == ARDUINO_ID )
    {
      byte ASCII =  result & 0x0F;
      DisplayTo7Seg( ASCII );
    }
  }
}

So if the bytes sent by your device are for example: 1,1,0,0,0,1,0,1 , the ID will be 1100, and the ASCII value will be 101.

Note, I'm beginner too so there may be a better way, or maybe my code won't even work :slight_smile:

9

I want to receive 8 bits of binary data on the hardware serial port

Bits, not bytes.

10

But a bit will be read as a byte by Serial.read()..Correct?

11

guix:
But a bit will be read as a byte by Serial.read()..Correct?

No.