general

Hello Robert,

Please refer to the following wiki link for how to use the sensor: https://wiki.dfrobot.com/Gravity__Analog_TDS_Sensor___Meter_For_Arduino_SKU__SEN0244.  In the 

Advanced Tutorial session, you will find two links, the library of the sensor and a tutorial on how to use the libraries. Click on the first link and the zip file will be automatically downloaded, in which you will find the header file you were looking for. Following the instruction in the second link, and you will be ready to go.

Have fun!