A while back I got some ultrasonic distance sensors from ebay:
The main idea was to try to use this as wind speed meter, but also curiosity how they did that at 5V DC, as I needed in other experiments many tens of volts for a reasonable signal.. Well, them Chinese are clever, they use the MAX232! Here is a circuit diagram:
By driving the piezo in a bridge from the RS232 output of the MAX232, they could get 24 Vpp (+12 to -12 V). The MAX232 does the voltage generation.
It is an old trick, I have used MAX232 to make a negative supply for some opamps once... But you never are to old to learn a trick, could be used for other things too, like alarm beepers.
This one shows the RX filter:
This sensor works very well actually, I removed the TX piezo side and put it 30 cm away with some wires, and was testing pulse length variations while making wind with a big fan, very hard to see, unknown micro ?
But for the sensors worth the money.
Replace micro and software, there is the ultrasonic wind speed meter.
Maybe it is already on ebay ;-)