Next, connect the INIT signal to the output bit you are using for the sonar unit. You will spend a lot of time trouble shooting if you forget to do this. This means that an object must be at least this distance from the sonar unit to be detected. You can get around this with some additional wiring and software. If you needed more accuracy up close, I usually use IR optics to detect something a few inches from my robot.
Some objects are harder to detect than others.
For example, walls are easy to detect and chair legs are hard to detect. I usually use three 7805 voltage regulators in parallel to power a sonar unit. Make sure you take into account the 2.38ms dead time. Do not expect a signal within this time period after pulling the INIT high. This takes around 1 minute after the solder iron is hot and well worth the time.