tasosstr:
I need this because i want to get the height of a petrol tank, so now i can have more better results because of you
Tasos, just a word of caution before you get too far into your project:
Ultrasonic sensors don't work well with petrol/gasoline. I seem to recall it was due to vapor in the tank giving false readings.
My wife used to work for ESI in Wichita, KS, which specialized in designing and installing liquid storage tank level sensors. They provided a business-to-business link where their hardware would monitor tanks of, say, liquid chicken feed additive, and automatically call the tank-filling-company and schedule a delivery when the tank was low.
I recall my wife talking specifically about a big sale hanging on their ability to monitor fuel tank levels, and the lead engineer was under a lot of pressure to develop a sensor that worked, but a solution eluded him and it was causing a lot of friction at work. This was many years ago, and it's now a solved problem, but the problem still stands for generic ultrasonic sensors. (It may have been a solved problem then, and maybe the boss didn't want to use a third-party product.)
There are commercial sensors available for measuring petrol/gasoline, but I'm sure they're at least a magnitude more expensive than the hobby ultrasonic sensors.