add: 补齐sht40的示例

https://gitee.com/openLuat/LuatOS/issues/I77NNS

demo/sht40/main.lua

@@ -0,0 +1,60 @@
+
+-- LuaTools需要PROJECT和VERSION这两个信息
+PROJECT = "sht40demo"
+VERSION = "1.0.0"
+
+-- sys库是标配
+sys = require("sys")
+
+-- 接线
+--[[
+SHT40 --- 模块
+SDA   -   I2C_SDA
+SCL   -   I2C_SCL
+VCC   -   3.3V
+GND   -   GND
+
+SHT40手册: https://www.mouser.cn/datasheet/2/682/Datasheet_SHT4x-3003109.pdf
+]]
+
+
+-- 启动个task, 定时查询SHT40的数据
+sys.taskInit(function()
+
+    local tmp,hum -- 原始数据
+    local temp,hump -- 真实值
+
+    local addr = 0x44
+    -- 按实际修改哦
+    local id = 0
+
+    log.info("i2c", "initial",i2c.setup(id))
+
+    while 1 do
+        sys.wait(400)
+        local serial_num = i2c.readReg(addr, 0x89, 6)
+        if serial_num and #serial_num ~= 6 then
+            break
+        end
+        log.info("sht40", "尚未检测到设备")
+    end
+
+    while true do
+        local tmp = i2c.readReg(addr, 0xFD, 6)
+        if tmp and #tmp == 6 then
+            local _,tval,crc1,hval,crc2 = pack.unpack(tmp,'>HbHb')
+            if tval and hval then
+                temp = (((17572 * tval) >> 16) - 4685)/100
+                hump = (((12500 * hval) >> 16) - 600)/100
+                log.info("SHT40", "temp,humi",temp,hump)
+            end
+        end
+        sys.wait(1000)
+    end
+
+end)
+
+-- 用户代码已结束---------------------------------------------
+-- 结尾总是这一句
+sys.run()
+-- sys.run()之后后面不要加任何语句!!!!!