is “Drishti” which can switch the system from an indoor to an outdoor environment and vice versa with a simple vocal command. To provide complete navigation system, authors extend indoor version of Drishti to the outdoor versions for blind pedestrians by adding only two ultrasonic transceivers that are smaller than a credit card and are tagged to the user’s shoulder. System provides a real-time communication between user and the mobile client via the headphone in which user can ask for the path, obstacle prompts, and even his/her current location in familiar or unfamiliar surrounding also. Unfortunately, this system has two limitations. As only two beacons attached to the user’s shoulder, so it becomes impossible to obtain the height data of the user. Used algorithm calculates the location of user in two dimensions assuming the average height of a person, which gives larger error if the user sits or lies down. Another limitation is that system uses only 4 pilots to wrap “Smart House”. Because of signals reflection or blocking by walls and furniture, there are some “dead spots” due to the bad information reads. Ref 03 …show more content…
is based on embedded system, uses ultrasonic sensor for distance measurement, IR sensor for object detection and AVR sound system for audio instructions. The main functions of this system are environment recognition and path detection. Ultrasonic sensors receive visual information and this visual information is transformed into auditory information. To represent the information about the position of obstacles audio components of intensity, frequency, binaural phase difference are used. This signal transformation system reduces the training time required to use a white cane. However, only issue of this system is the difficulty to know one’s location globally. Audio