08-08-2012, 12:50 PM
Discrete Distance and Water Pit Indicator using AVR ATmega8 in Electronic Travel Aid for Blind
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Abstract
The present electronic travel aid device consist usually available ultrasonic sensor to detect obstacles on the way within a distance of two to three meters. It transmits ultrasound beams at a regular time interval. If any object is present on the way, the emitted ultrasound will be reflected back to the sensor. The discrete distance of the object is then measured according to discrete levels of 1, 2 and 3 meter and sensed by tactile vibrators. In addition to this, device is to give information about water pits in the traveling path which is sensed by audio signal.
Introduction
Mobility for the blind can be defined as the ability to move with ease, speed and safety through his environment independently. It is estimated that there are 180 million people in the world currently who are affected by problems with their vision. Within this number, approximately 40 – 45 million are blind, by definition not able to walk unaided. With an estimated 7 million people going blind each year, the number of people visually impaired is expectedly to double by the year 2020[1]. Looking at this locally, we see that within Australia, it is estimated that there are 380 thousand people who have low vision or are classed as legally blind. A person who cannot see at 6 meter nor has a field vision of 10° or less is considered legally blind. 95% of people classed as legally blind have some vision. To be classed as blind, there is a total loss of vision. Low vision cannot be corrected by visual aids such as glasses and contacts [2]. With the general population living longer due to advances in medical technology, more people are being affected by age-related macular degeneration (AMD). This is a leading cause of blindness on the developed countries with an estimated 25 – 30 million people affected worldwide. This number is expected to triple in the coming 25 years. AMD causes the degeneration of central vision, leaving only peripheral view. This is caused by damage to the damage to the retina and hence cannot be corrected. While it rarely causes blindness, it can deteriorate into severe cases causing large disruption to normal life.
Disadvantages of the Present Devices
Sonic pathfinder a head mounted device, on the other hand produces audio signal of different frequencies but not designed to detect any hanging object. Moreover a blind person having hearing acuity may be unable to use it properly due to the absence of any tactile sensor. Distance information between blind person and object is missing in these devices because intensity of audio signal or tactile vibration is uniform as blind person is approaching towards object. Accepts this there is no provision for finding dig and water pits information in these devices.
Suggested Device
The suggested device uses ultrasonic sensor SRF04 and can detect any object that lies on the ground or hanging from top, situated a distance of 3 meters from the user. The minimum size of the object that can be detected should not be less than 3 cm width (or diameter). In operation a beam of ultrasound of 40 KHz frequency is transmitted at a regular interval in the forward direction. The ultrasound will be reflected from a nearby object.
Block Diagram
Figure 1, shows the complete block diagram of the suggested device. Once triggered the sensor will generate and transmit ultrasound in the forward direction. This ultrasound will be reflected back to the sensor if any object is present within 3 meter range. The time taken by the ultrasound to travel to and back from the obstacle is measured by a counter using specific clock frequency. Again for continuous distance measurement the ultrasonic sensor should be triggered at a regular time Interval and the counter inside microcontroller should also be reset accordingly. The counter output of microcontroller is then decoded and interfaced appropriately with output devices. This produces one of the two audio signal either for water pit or for low battery indication and to activate tactile vibrator to indicate discrete distance of 1 or 2 or 3 meter.
Ultrasonic Sensors
It is the heart of the suggested device. We have used ultrasonic sensor type SRF04, known as ultrasonic range finder [10]. The SRF04 is a light weight ( of 0.4 Oz), small size ( 4 cm wide, 2 cm height and 1.5 cm depth) sensor and produces ultrasound of 40 KHz frequency and has built-in transmitter and receiver. It operates from 5 V DC and consumes 30 mA to 50 mA current. The maximum range of this sensor is 3 meters. This sensor can detect a stick having diameter of 3 cm from a distance of 2 meters or more.
This SRF04 uses a microcontroller and requires an input trigger pulse of minimum 10 micro second widths. In operation the processor of SRF04 waits for a trigger pulse. After receiving a proper trigger pulse the processor will generate eight cycles of sonic burst of 40 kHz.
Experimental Results
Error measurement of different shape Obstacles:
In this system, new pulses are transmitted as soon as the echo from the previous pulse is detected. After transmitted, previous pulses are processed before interrupted by the new pulses. Therefore, scan interval is 50ms which emitted energy can be reached at round-trip distance 10m four representative objects were chosen to verify the accuracy of the distance measurement.
The objects included flat panel of 80 by 60cm, coal-tar cylinder of 13cm diameter, steel pole of 3cm diameter, and sweater. As can be seen from fig.4, the distance measurement data for the flat panel have shown a low relative error of around 2%.
Conclusion
This designed Electronic Travel Aid uses ultrasonic sensors. These sensors are capable of detecting obstacle maximum at 2-3 fit; this is light weight device and includes ultrasonic sensors and few electronic components with long life battery. The broad beam angle ultrasonic sensors enable wide range environment recognition. The main functions of this system are the clear path indication and the environment recognition.