Controlling an Arduino with Perl

Outline

  • Quick intros on Arduino
  • Quick intros on Firmata
  • Quick intros on Demo Perl Library
  • Practical Example - Specifications Parsing

What's an Arduino?

  • Hobbyist's Microcontroller Development Platform
  • Both Hardware and Software

Arduino's Hardware (One example!):

One part uC...

Arduino's Software:

Another part IDE...

Quick Arduino Example (Blink):

void setup() {                
  pinMode(13, OUTPUT);  // LED is connected to pin 13
}

void loop() {
  digitalWrite(13, HIGH);   // set the LED on
  delay(1000);                  // wait for a second
  digitalWrite(13, LOW);    // set the LED off
  delay(1000);                  // wait for a second
}

Why's Arduino Cool?

  • Easy
  • Mindshare
  • Support and Accessibility

Firmata:

http://www.firmata.org
"Firmata is a generic protocol for communicating with microcontrollers from software on a host computer. It is intended to work with any host computer software package."

In pragmatic terms...

System to control Arduino I/O pins from a computer.

Control Example

Firmata GUI Clients

How does it work?

  • Arduino runs host code
  • Computer runs client code
  • Serial communication

Serial Communication Protocol

  • MIDI usually used for electronic instruments
  • Redefine MIDI messages for I/O

MIDI for Firmata

  • 8-bit protocol
  • Top bit indicates data or command
    c/d 0 0 0 0 0 0 0 0
  • Variable packet length
  • Has interruptible data-stream mode

Example Firmata Protocol

  • Digital Pin 11 On
    HEX c CMD PORT
    0x91 1 0 0 1 0 0 0 1
    0x04 0 0 0 0 0 1 0 0
    0x00 0 0 0 0 0 0 0 0
  • v2.1 Protocol

Perl Based Interface

Work in progress: Device::Firmata

  • Spartan interface
  • Use Device::SerialPort

Example: Blink

use Device::Firmata;
use Device::Firmata::Constants qw/:all/;

my $device = Device::Firmata->open('/dev/ttyUSB0');

$device->pin_mode(13=>PIN_OUTPUT);
while (1) {
    $device->digital_write(13=>1);
    sleep(1);
    $device->digital_write(13=>0);
    sleep(1);
}

Non-demonstrated Features

  • Digital Input - $device->digital_read($pin)
  • Analog Input - $device->analog_read($pin)
  • PWM! - $device->analog_write($pin)

Practical Uses?

  • I/O for desktop applications (Very Poor Man's Labjack)
  • Education/Study

Example: Interface Exploration

Sure Electronics: Red LED Matrix Board
- 32x8 matrix
- Driver IC: HT1632
- Specifications...

HT1632 Specifications

Ugh.

 

Prototyping the Interface

  • Avoid save, compile, upload, reset, disappointment cycle!

SO:

  • Use Firmata to link Arduino and Perl
  • Write signal implementation in Perl

Connection Diagram

Connection Diagram

Logic Timings

Game Plan

  • 1. Strobe CS pin
  • 2. Clock data in
  • ???
  • 4. Profit! Display cool things!

Pin Strobe Code

# $pin = pin connected CS
# $PULSE_LEN = 0.001s

$device->digital_write($pin=>1);
select undef, undef, undef, $PULSE_LEN;
$device->digital_write($pin=>0);
select undef, undef, undef, $PULSE_LEN;

Data Writing

# $data_pin = connected DATA line
# $wr_pin = connected to WR line
# $PULSE_LEN = 0.001s

$device->digital_write($data_pin=>$v);
$device->digital_write($wr_pin=>1);
select undef, undef, undef, $PULSE_LEN;
$device->digital_write($wr_pin=>0);
select undef, undef, undef, $PULSE_LEN;

Applied Example

  • Full detail of code not discussed.
  • Can draw lines!
  • Can draw graphs!
  • Can draw words!

Prototyping!!!

  • Bandwidth limitations
  • MIDI interpreter limitations
  • Computer controlled microcontroller?!

Summary

  • Arduino = Cool Prototyping Platform
  • Firmata = Cool Protocol to control Arduino
  • Perl = RAD tool to script interactions with the real world

Presentation Tool

Used jQuery plugin by Trevor Davis:

http://bako.ca/pm/firmata

??