temper-hidapi.rb

require 'ffi'

vendor_id = 3141
product_id = 29697

module HidApi
  extend FFI::Library
  ffi_lib 'hidapi'
 
  attach_function :hid_open, [:int, :int, :int], :pointer
  attach_function :hid_write, [:pointer, :pointer, :int], :int
  attach_function :hid_read_timeout, [:pointer, :pointer, :int, :int], :int
  attach_function :hid_close, [:pointer], :void
end
 
device = nil
10.times do
  device = HidApi.hid_open(vendor_id, product_id, 0)
  unless device.address == 0
    break
  end
end
if device.address == 0
  raise 'Failed to get device handler after 10 retries'
end
 
res = HidApi.hid_write(device, [0x01, 0x80, 0x33, 0x01, 0x00, 0x00, 0x00, 0x00].pack('C*'), 8)
raise "Command write failed" if res <= 0
 
buffer = FFI::Buffer.new(:char, 4)
res = HidApi.hid_read_timeout(device, buffer, 4, 1000)
raise "Command read failed" if res <= 0
data = buffer.read_bytes(4).unpack("C*")

rawtemp = (data[3] & 0xff) + (data[2] << 8)
if (data[2] & 0x80) != 0
  rawtemp = -((rawtemp ^ 0xffff) + 1)
end

temp_c = rawtemp * (125.0 / 32000.0)
puts temp_c