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ISSN (Online) : 2278-1021
ISSN (Print) : 2319-5940
International Journal of Advanced Research in Computer and Communication Engineering
Vol. 3, Issue 11, November 2014
Public Transport Assistant for Visually Impaired
(PuTAVI)
Sathvik N Prasad1, Shrikanth S Hegde1, Subodh B Hegde1, Vishwas H P1, Sreekar V1,Roopa J2,
Govinda Raju M2
Student, ECE, RV College of Engineering, RV Vidyaniketan Post, Mysore Road, Bangalore, India1
Assistant Professor, ECE, RV College of Engineering, RV Vidyaniketan Post, Mysore Road, Bangalore, India2
Abstract: Visually challenged people rely on support for managing their routine, be it in crossing busy roads, climbing
steps or boarding buses. Applying technology to make these people self-reliant and independent is a social
responsibility. It is high time that a novel technological solution be found. The objective of this project is to provide
technologically supported audio guidance system to visually challenged people, with respect to obstacle and bus
identification on an MSP430 platform making use of ultrasonic sensors, RF Transmitter and Receiver. The system is
wearable by the user and user friendly in its interface.
Keywords: Signal Conditioning; Audio playback; Obstacle Detection System; Bus Identification System; Ultrasonic
sensors
I. INTRODUCTION
This project is oriented towards helping visually impaired
people with appropriate voice commands that are played
through an earphone. The proposed design is the
architecture of a new concept we have christened
"PuTAVI". The project aims at making navigation and
commutation smoother and easier for these people by
administering a sub system which gives audio information
about the route numbers of local transport (bus in this
case). The advantage of the system lies in the fact that it
can prove to be a cost effective solution to millions of
blind people worldwide. The proposed combination of
various working units as shown in Figure1, makes a real-time
system that monitors position of the user and
provides appropriate voice information, making navigation
more safe and secure.
A .Technical Background
Recently there has been a lot of Electronic Travel Aids
(ETA), designed and devised to help the blind people to
navigate safely and independently. The most important
factors, which enable blind users to accept these devices
readily, are portability, low cost, and above all simplicity
of controls. Hence, ETA device should be small in size
and lightweight for portability.
Figure 1: Top Level Block Diagram
Since a blind person is not able to see the display panel or
control buttons, hence the device should be easily
controllable. Moreover, the ETA device should be of low-cost
so as to be affordable by a common man. Recent
trends showcases a wide range of research work initiated
in the direction of designing high end and electronically
advanced robotic guides which can not only provide safe
navigation but these aids have intelligent interfaces that
provide simple physical and cognitive assistance such as
obstacle avoidance and public transport assistance.
B. Proposed Solution
In comparison with other technologies many blind
guidance systems use ultrasound because of its immunity
to the environmental noise. Another reason why ultrasonic
is popular is this technology is relatively inexpensive, and
also the ultrasound emitters and detectors are small
enough to be carried without the need for complex
circuitry. Apart from the conventional navigation systems,
a blind aid system can be provided a new dimension of
Real-time-assistance and artificial vision along with
dedicated obstacle detection circuitry.
C. Organization of the Paper
Section 2 of the paper substantiates the proposed solution
provided. It throws light on the major hardware and
software sub-systems. Section 3 elucidates the hardware
implementation and the software logic. Section 4 of the
paper provides the results of simulations. Section 5 deals
with the scope for improvement in the project.
II. PROPOSED SOLUTION
Figure 2 represents the System Level Diagram of PuTAVI.
Since a prototype has been presented the assumptions made
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ISSN (Print) : 2319-5940
for the input is from 2 buses and hence a unique audio is
played for each of the buses.
The main constraint in the system was to consider that a
transmitter is present on the bus which has to be detected.
The main hardware parts in the circuit are as follows:
 Sensors
 Signal Conditioning
 Microcontroller
 Audio Playback IC
 RF Decoder and receiver
 User Controlled Switch
The software in the system mainly considers the code
which governs the working of the subsystems. The
software used in developing the above system are:
 Code Composer Studio, Version 5.2.1
 Termite Serial Monitor
 TINA TI Version 9
The analog subsystem is a 5V to 3.3V converter. This
converter helps in conditioning the sensor output in order
to provide input to MSP430, for processing.
Figure 2: System Level Diagram
III. IMPLEMENTATION
A. Hardware Implementation
The overall hardware mainly is classified into power-supply
unit, sensor system, signal conditioning,
microcontroller, R. F. transmission and reception along
with encoder and decoder, and the audio logging and
playback unit.
 Power Supply unit:
The power-supply unit consists of 2 regulators namely
LM3940 and UA7805. The 5 volt output got after the
regulation is used to power the sensor unit, signal
conditioning, RF and the audio sub-system. The 3.3 volt
output is used to power the msp430 microcontroller.
 Sensor unit:
The Sensor unit consists of 2 ultrasonic sensors (HC-SR04).
To start measurement, a pulse of high(5V) for 10us is sent
to TRIG pin of SR04 ,this will initiate the sensor which
transmits 8 cycles of ultrasonic burst at 40Khz and wait
for the reflected ultrasonic burst.When the sensor detects
ultrasonic reflection from receiver, the echo pin is set to
5V and the duration of it is proportional to the distance of
the reflecting object as shown in Figure 3.
Figure 3: Timing waveform of HCSR-04
According to calibrations of the sensor the distance in cm
is equal to the 1/58 times the durarion for which the echo
pin is set high.
 Signal Conditioning unit:
푣표푢푡 = 푎 × 푣푖푛 + 푏 ------ (1)
Design Requirements:
Vout=3.3 V when Vin=5V
Vout=0 V when Vin=0V
Substituting in Eqn(1)
We get a=3.3/5; b=0; Designing a=3.3/5 considering
Standard resistance values and tolerances:
a= R1/ (R1+R2)
R1=330 KΩ
R2=170 KΩ~169.7 KΩ
(150 KΩ+15 KΩ+4.7 KΩ; standard values)
The circuit designed is shown in Figure 4.
Selection of op-amp:
Since we need a unipolar swing in the output of the circuit;
a single supply op-amp circuit has been designed for the
above use. The OPA4277PA was chosen in order to
optimise the space as the package consists of 4 op-amps
with improved noise immunity and a good slew rate.
Since the pulse width of the sensor is as less as 10us the
op-amp used to shift the level should have a good slew
rate. The specifications of OPA4277PA just proved
perfect for the above application.
Figure 4: OpAmp 4277 5V to 3.3V converter for Signal Conditioning

ISSN (Print) : 2319-5940
 RF unit:
Encoder: The 212 series of encoders begin a 4 word
transmission cycle upon receipt of a transmission enable.
The HT12E and the transmitter circuit is as shown in
figure 5.
Figure 5: HT12E encoder circuit with RF Transmitter
This cycle repeats itself as long as the transmission enable
is low. Once the transmission enable returns high the
encoder output completes its final cycle and then stops.
The transmission timing is as shown in Figure 6.
Figure 6: Timing waveform of RF Transmitter
Decoder:
Figure 7: Receiver circuit with Decoder
The 212series of decoders provides various combinations
of addresses and data pins in different packages so as to
pair with the 212 series of encoders.
 Microcontroller MSP430G2553
The Microcontroller used in the project is
MSP430G2553.The MC is mainly used to synchronize all
the sub-systems. The function served by the
microcontroller is mainly to trigger the ultrasonic sensors
and then wait for the echo pulse from the sensor. At first a
user controlled switch is provided as an input to the
microcontroller. The user can switch between obstacle
detection and bus identification mode. Based on this
decision the MC controls the audio feedback system with
corresponding and relevant messages as previously
logged.
 Audio Playback System(APR33A3)
The Audio playback system gives appropriate voice
commands to the VI person through earphone. The system
consists of a powerful 16 bit audio processor (APR33A3)
which has a built in high resolution ADC and DAC. The
system also has an audio recording microphone amplifier
through which the user can record the voice messages at 8
different channels. In this project we used only four voice
commands left, right, busnumber1 and bus number 2
which are recorded at 4 different channels. The recorded
voice can be played back by selecting respective channels
through MSP430 micro-controller.
The final product is made wearable and is compact. It is
portable and light to carry around for outdoor navigation.
The finished product PuTAVI is as shown in the Figure 8.
Figure 8: Finished Product PuTAVI
B. Software Implementation
The logic flow of the circuit is shown in the following
block diagrams.
The system level flowchart is as shown in Figure 9.

ISSN (Print) : 2319-5940
Figure 9: System Flow chart
The user is given a switch to choose between the modes.
Two modes have been provided:
 Obstacle Detection System
 Bus Identification System
Both the systems are controlled by MSP430 and share a
common output through the audio feedback system.
The logic flow of the Obstacle Detection System is as
shown in the flowchart in Figure 10.
The device is calibrated such that the obstacle is sensed
only when it is at a particular distance from the user.
The decision making in all the stages of logic flow is done
by the microcontroller MSP430.
Figure 10: Obstacle Detection System flowchart
The logic flow of the Bus Identification System is as
shown in Figure 11.The bus identification system is a pair
of RF Transmitter and Receiver. When the bus approaches
the bus stop the RF transmitter sends a message which is
picked up by the receiver and decoded. This information is
given to the user via audio feedback. The user decides
accordingly. The merit of the decoder is that 212 buses can
be detected.
Figure 11: Bus Identification System flowchart
IV. RESULTS
The simulation result of the signal conditioning circuit
designed using OPA4277PA is shown below. The purpose
of the circuit is to level shift the signal from 5V to
3.3V.The result is shown in Figure 12.
Figure 12: Simulation results of level shifter
The ultrasonic sensors were calibrated using Termite 2.9.
The circuit is calibrated for an optimum distance. The
screen grab of the above calibration is as shown in Figure
13.

ISSN (Print) : 2319-5940
Figure 13: Calibration and testing of Ultrasonic sensor
HCSR-04
V. CONCLUSIONS
The system provides an integrated solution of both
obstacle detection and public transport assistance. The
main objective of the system was to make the system
compact, low power and wearable, which has been
accomplished. Since a prototype of the product is
presented, it has been limited to an extent of 2 buses. This
can be extended to any form of transport and number.
The user can select the mode of his choice i.e., between
obstacle detection and public transport assistance. The
overall product is compact and low power, and hence can
be carried around with minimum effort and least concern
regarding powering of the circuit.
When low cost isn’t a priority the system can be made
robust with the use of a GPS module. The audio playback
can be made clearer and the storage capability can be
increased with the help of SD card. The use of SD card
was intended but the logging and playback was too slow.
We had two options on hand; that was to change the
platform or to change the approach for audio playback.
We went ahead with the use of audio playback
ICAPR33A3; this can be done better with the help of a SD
card and a more improved platform with enhanced
capabilities.
REFERENCES
[1]. Amit Kumar, RushaPatra, M. Manjunatha, J.Mukhopadhyay and A.
K. Majumdar An electronic travel aid for navigation of visually
impaired Communication Systems and Networks (COMSNETS),
2011 Third International conference on 4-8 Jan 2011.
[2]. Calder, David J.; Curtin .An obstacle signaling system for the blind
,Digital Ecosystems and Technologies Conference (DEST),
2011Proceedings of the 5th IEEE International,Conference on 30
June 2011.

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