dymo.rb

require 'libusb'

VENDOR_ID = 0x0922
PRODUCT_ID = 0x8003
SCALING_FACTOR = 0.1

usb_context = LIBUSB::Context.new
device = usb_context.devices(idVendor: VENDOR_ID, idProduct: PRODUCT_ID).first
unless device
  puts 'Device not found'
  exit 1
end
begin
  handle = device.open
  handle.detach_kernel_driver(0)
rescue
ensure
  handle.close
end
endpoint = device.endpoints.first
handle = device.open
loop do
  data = handle.interrupt_transfer(endpoint: endpoint, dataIn: 0x0006, timeout: 100)
  # data.bytes[1]: 4 is negative, 2 is zero, 5 is positive
  case data.bytes[3]
  when 0 # kg mode
    grams = data.bytes[4] + (256 * data.bytes[5])
    puts "weight: #{data.bytes[1] == 5 ? '-' : ''}#{grams}g"
  when 255 # lb mode
    ounces = SCALING_FACTOR * (data.bytes[4] + (256 * data.bytes[5]))
    puts "weight: #{data.bytes[1] == 5 ? '-' : ''}#{'%.1f' % ounces}oz"
  end
  sleep 1
end
handle.close