I want to put more digital sensors, how can I do it?

Port Splitter for NXT Digital Sensors (SPLIT-Nx-v2). This simple device allows you to connect three compatible I2Cs to a single sensor port. It will work with one of four sensor ports on an EV3 or NXT.

The ports of the SPLIT-Nx-v2 are not labeled, you can connect the brick and the sensors to any port (because the SPLIT-Nx-v2 sends its four ports together). You can find a long list of supported sensors on the product page.

You can connect up to three I2C devices to an NXT or EV3 port. It only works with I2C compatible devices. It is supported in EV3-G, NXT-G, NXC, RobotC, JOS, LabVIEW, LVEE