We are trying to connect SDI-12 sensors., not modbus. Sensors which we try to connect are EnviroPro EP100G. They are measuring Temperature, soil moisture and Ec. They are 40 cm long and on each 10 cm they have sensors for those three measurement. There are two sensors connected to bus, eg data pin. With script which I send it to You it is working, measuring but this is only for one sensor. Sensors have unique address 1 and 2 . We know how to change address of sensor. When we put before command C, C1, C2 or C3, question mark ?, it does not measure anything. When we change in file sensor address from 2 to 1, it works again reading from sensor with address 1. In another reply I will send You file with EnviroPro SDI-12 commands. We connect them in variant supplying sensor with 5V from Arduino 2560 and supplying sensor with 12V from separate power supply.In variant with 12V, power supply is 2A, so issue with current is not a problem. It is only working with this example, which I attach. When we load and compile in Arduino 2560 Your examples for SDI-12, it does not work, eg dont measure anything. We try with other pins as well, eg pin 2 and 3, no measurement. It is same situation with some other examples which we find on net for SDI-12. They dont work. We want to use Your MyFly data logger in our project, but we want to be sure, that we can measure. Please help with some code or explanation, what we are doing wrong. Please help with some code or advice.