barkest_lcd

BarkestLcd

This gem is designed to make it easy to interface with some LCD displays.

I wanted to add a front panel LCD to a server I was building, so I started this project to address interacting with the LCD panel I picked up.

Currently it works with the PicoLCD from www.mini-box.com.

Installation

This gem depends on HID API.

Installation of the dependency is specific to the environment.

For OS X (using homebrew):

$ brew install hidapi

For Ubuntu/Debian:

$ sudo apt-get install libhidapi-libusb0
$ cd /usr/lib/x86_64-linux-gnu
$ sudo ln -s libhidapi-libusb.so.0.0.0 libhidapi.so

Add this line to your application's Gemfile:

gem 'barkest_lcd'

And then execute:

$ bundle

Or install it yourself as:

$ gem install barkest_lcd

Usage

Let's assume you have one picoLCD 256x64 device attached to your computer. Usage is fairly simple.

This example will draw a 32x32 rectangle with an X in it.

my_device = BarkestLcd::PicoLcdGraphic.first
my_device.open
my_device.draw_rect(40, 4, 32, 32).draw_line(40, 4, 72, 36).draw_line(40, 36, 72, 4)
my_device.paint

As you can see, most of the methods are chainable. Unless the method has an explicit return value (like open?) then the method should be returning the device model. The open, close, and paint methods are all chainable as well.

There are currently some very basic drawing methods included by the SimpleGraphic module. These include set_bit, draw_vline, draw_hline, draw_line, and draw_rect. The clear method will clear the screen.

Continuing, we will wait for the user to press the OK button.

OK_BUTTON = 6
ok_pressed = false

# set the callback to process keys when they are released.
my_device.on_key_up do |key|
  if key == OK_BUTTON
    ok_pressed = true
  end
end

# use the "loop" function to process events with the device and update the screen.
until ok_pressed
  my_device.loop
end

In this case we set the on_key_up callback to set a flag when the OK button is pressed. If we wanted to do repeating keys when a user holds down a button, we may want to set the on_key_down or use the key_state method within the loop.

Finally, I recommend closing the device when you are finished. Ruby will close the device when it exits, but if you are handling errors and such, closing the device explicitly in an ensure block will help to protect you against being unable to open the device again.

my_device.clear.paint
my_device.close

It is not necessary to clear the screen before closing, but doing so ensures that you do not leave weird information or screen artifacts up when your application is done.

Credits

• The picoLCD 256x64 Suite Source provided most of the information needed to make this gem interact with the picoLCD 256x64 from mini-box.
• The picoLCD256x64 project provided some inspiration, but I ended up going a completely different direction.
• The font came from Silkscreen.

License

Copyright (c) 2016 Beau Barker

The gem is available as open source under the terms of the MIT License.