Sonar Module Multiwii Naze32 or Arduino.
These modules can be used with the Naze32 for Sonar based altitude hold.
More to come on how to hook this up, but there is plenty of documentation out there on the Multiwii forums.
a little bit on how it works:
There are 4 pins out of the module : VCC , Trig, Echo, GND .
It’s very easy interface for controller to use it ranging/ altitude hold..
The all process is : pull the Trig pin to high level for more than 10us impulse , the module start ranging ; finish ranging , If you find an object in front , Echo pin will be high level , and based on the different distance,it will take the different duration of high level. So using this information you can figure out the distance by using the following formula:
Distance = ((Duration of high level)*(Sonic :340m/s))/2