Liuyuan Chen and Zeynep Basaran from Cornell University have implemented an interesting project called SensCap as their final year curriculum. SensCap is a device that guides the visually impaired around obstacles. It provides stereo information about obstacles near and around the head. It consists of two modules: A baseball cap worn on the head for user feedback and a zipper hip-pack to switch between the output modes.
Senscap uses two ultrasonic sensors and a microcontroller to sense obstacles and generate an output. The output can either be a sound signal from the headphone or vibration of mini motor. There exists a user-flexibility in switching the output mode from the headphone-feedback to motor vibration. The two sensors placed at different angles provide stereo information on obstacles in front of the user. That is, on approaching the obstacle the user would know which path to take to avoid collision.
The logical flow of the project is as follows:
· The user control
· Sensor control
· Sensor interpretation
· Output to the user.
The sensors used here are two Senscomp 6500 each with its own transducer for transmitting and receiving. They are capable of sensing within a beam angle of seventeen degrees. An initialization signal (INIT) is send from the microcontroller ATMega644 to control the sensors. Whenever the Senscomp 6500 receives an INIT, it transmits 16 pulses using transducer and receives the pulses that come to it after reflection from the obstacle. This sets off for the generation of an Echo signal. The two sensors are interspersed to avoid crosstalk. Only one sensor is active at a time. They are meant to serve the user in two directions; left and right.
The microcontroller brain is used to initialize the sensors and process the sensor output. Two of the controller’s timers are used to generate pulse width modulated signal for the use output while the timer is used for the input capture for interpreting the sensor results.
The user control is integrated on the hip-pack. It has three switches. The first switch is to switch the microcontroller on/off, the second switch turns the sensors on and the third switch is meant to switch the output mode of the device.