diff --git a/lua_modules/liquidcrystal/lc-gpio4bit.lua b/lua_modules/liquidcrystal/lc-gpio4bit.lua
index 290a96ee..4a682dbc 100644
--- a/lua_modules/liquidcrystal/lc-gpio4bit.lua
+++ b/lua_modules/liquidcrystal/lc-gpio4bit.lua
@@ -56,25 +56,25 @@ return function(bus_args)
    -- Return backend object
    return {
       fourbits  = true,
-      command   = function (screen, cmd)
+      command   = function (_, cmd)
          return send4bitGPIO(cmd, false, false, false)
       end,
-      busy      = function(screen)
+      busy      = function(_)
          if rw == nil then return false end
          return bit.isset(send4bitGPIO(0xff, false, true, true), 7)
       end,
-      position  = function(screen)
+      position  = function(_)
          if rw == nil then return 0 end
          return bit.clear(send4bitGPIO(0xff, false, true, true), 7)
       end,
-      write     = function(screen, value)
+      write     = function(_, value)
          return send4bitGPIO(value, true, false, false)
       end,
-      read      = function(screen)
+      read      = function(_)
          if rw == nil then return nil end
          return send4bitGPIO(0xff, true, true, true)
       end,
-      backlight = function(screen, on)
+      backlight = function(_, on)
          if (bl) then gpio.write(bl, on and gpio.HIGH or gpio.LOW) end
          return on
       end,
diff --git a/lua_modules/liquidcrystal/lc-gpio8bit.lua b/lua_modules/liquidcrystal/lc-gpio8bit.lua
index d61a06f9..43b7ffd3 100644
--- a/lua_modules/liquidcrystal/lc-gpio8bit.lua
+++ b/lua_modules/liquidcrystal/lc-gpio8bit.lua
@@ -53,25 +53,25 @@ return function(bus_args)
    -- Return backend object
    return {
       fourbits  = false,
-      command   = function (screen, cmd)
+      command   = function (_, cmd)
          return send8bitGPIO(cmd, false, false, false)
       end,
-      busy      = function(screen)
+      busy      = function(_)
          if rw == nil then return false end
          return bit.isset(send8bitGPIO(0xff, false, true, true), 7)
       end,
-      position  = function(screen)
+      position  = function(_)
          if rw == nil then return 0 end
          return bit.clear(send8bitGPIO(0xff, false, true, true), 7)
       end,
-      write     = function(screen, value)
+      write     = function(_, value)
          return send8bitGPIO(value, true, false, false)
       end,
-      read      = function(screen)
+      read      = function(_)
          if rw == nil then return nil end
          return send8bitGPIO(0xff, true, true, true)
       end,
-      backlight = function(screen, on)
+      backlight = function(_, on)
          if (bl) then gpio.write(bl, on and gpio.HIGH or gpio.LOW) end
          return on
       end,
diff --git a/lua_modules/liquidcrystal/lc-i2c4bit.lua b/lua_modules/liquidcrystal/lc-i2c4bit.lua
index 2b299481..5036026a 100644
--- a/lua_modules/liquidcrystal/lc-i2c4bit.lua
+++ b/lua_modules/liquidcrystal/lc-i2c4bit.lua
@@ -73,26 +73,26 @@ return function(bus_args)
    -- Return backend object
    return {
       fourbits  = true,
-      command   = function (screen, cmd)
+      command   = function (_, cmd)
          return send4bitI2C(cmd, false, false, false)
       end,
-      busy      = function(screen)
+      busy      = function(_)
          local rv = send4bitI2C(0xff, false, true, true)
          send4bitI2C(bit.bor(0x80, bit.clear(rv, 7)), false, false, false)
          return bit.isset(rv, 7)
       end,
-      position  = function(screen)
+      position  = function(_)
          local rv = bit.clear(send4bitI2C(0xff, false, true, true), 7)
          send4bitI2C(bit.bor(0x80, rv), false, false, false)
          return rv
       end,
-      write     = function(screen, value)
+      write     = function(_, value)
          return send4bitI2C(value, true, false, false)
       end,
-      read      = function(screen)
+      read      = function(_)
          return send4bitI2C(0xff, true, true, true)
       end,
-      backlight = function(screen, on)
+      backlight = function(_, on)
          backlight = on
          local rv = bit.clear(send4bitI2C(0xff, false, true, true), 7)
          send4bitI2C(bit.bor(0x80, rv), false, false, false)