Sensor

Pressure is used to calculate depth at which rov operates.
Pressure at 1m is equal to 0.098bar, at 100m it is 9.8bar. In real world depth and pressure relationship isn’t constant. It depends on location, water temperature, salinity, etc. You can read more in this article "A Sea Water Equation of State Calculator".

Navigation in the underwater environment is not as easy as on the ground. You have only images from a camera, no sun, no characteristic points, water is not as clear as the air.

Expensive commercial vehicles uses sonar, but for homebuilt ROV an old fashioned compass is enough.

There are two main solutions using:

• analog compass
• digital compass

It is worth to mention that you must be careful installing a compass in the robot.

One of the best methods to visualize ROV data is to show them as overlay on images from camera.
This project can be used in any ROV. It presents data read from sensors mixed with video signal from camera. It can read data from analog 4-20mA sensors and from I²C chips. Although project assume usage of specific sensors, any I²C or 4-20mA sensors can be used. Only software needs small modifications.