I recently switched from using plain Atmel chips to Arduino. Arduino is a development platform that uses an Atmel Atmege168 chip. It simplifies things a lot.

The Arduino board has a USB port. It has a built in FTDI chip for USB to serial conversions.

This HOWTO shows how to communicate between Perl/Linux and the Arduino. Because of the Arduinos FTDI chip, I can use regular serial communication, I just needed to first set up the USB serial adapter drivers. Most modern linux distro should come with them installed.

The perl script will transmit a number, starting at 0, to the Arduino. The Arduino will then echo that number back to your linux/perl computer.

# Sample Perl script to transmit number
# to Arduino then listen for the Arduino
# to echo it back

use Device::SerialPort;

# Set up the serial port
# 19200, 81N on the USB ftdi driver
my $port = Device::SerialPort->new("/dev/ttyUSB0");
$port->databits(8);
$port->baudrate(19200);
$port->parity("none");
$port->stopbits(1);

my $count = 0;
while (1) {
    # Poll to see if any data is coming in
    my $char = $port->lookfor();

    # If we get data, then print it
    # Send a number to the arduino
    if ($char) {
        print "Recieved character: " . $char . " \n";
    } else {
        sleep(1);
        $count++;
        my $count_out = $port->write("$count\n");
        print "Sent     character: $count \n";
    }
}

Sample C program for Arduino. Listen for input on serial port then echos the input back out.

#include 
#include 

char incomingByte;              // for incoming serial data
char str1[50];
int count = 0;

void
setup ()
{
  beginSerial (19200);
  digitalWrite (13, HIGH);      //turn on debugging LED
}


//  MAIN CODE
void
loop ()
{
  // send data only when you receive data:
  if (Serial.available () > 0)
    {
      // read the incoming byte:
      incomingByte = Serial.read ();

      // Store it in a character array
      str1[count] = incomingByte;
      count++;

      // check if we have over 49 characaters or we recieve a return or line feed
      if (count > 49 || incomingByte == 10 || incomingByte == 13)
        {
          // Send the string back
          Serial.print (str1);
          count = 0;
        }
    }
}