28-12-2012, 04:41 PM
Low Power Microcontroller Based Simple Smart Token Number Display System
1Low Power Microcontroller.pdf (Size: 867.89 KB / Downloads: 91)
Abstract:
The inconvenience encountered in many public dealing
places like restaurants, banks, canteens etc. where people
normally follow queue system has called for many solutions to
speed up and ease the dealings. In this paper we show a low
power microcontroller based smart token number display system
to overcome the inconvenience mentioned above. This system is
used to display two digit numbers from 0 to 99 using two sets of
display units, one being user display and the other, customer
display. Using this system the customers need not wait in the
queue but come to get their order once their token number is
displayed in the large customer display. It consists of two
portions: a display unit and a processing unit. The software
design in the processing unit is accomplished using PIC16F877A
microcontroller. The power saving mode is achieved by putting
the microcontroller in sleep mode. A peripheral keypad is
interfaced with the microcontroller. Each set of display unit
consists of two seven segment displays which get input from a
BCD decoder/driver operating in open collector configuration.
The token number display system with low power mode
mentioned here is unique in the sense that it is controlled by
software to go in sleep mode to save power.
INTRODUCTION
In our university campus canteen token numbers are
announced using microphone. It causes lot of confusion due to
similarity in phonetics; such as ‘seventeen’ and ‘seventy’
sounds alike. Moreover customers sitting far from the counter
are unable to hear the numbers being announced vocally. It is
always observed that visuals catch attention immediately and
clearly than acoustics. The present situation demands a token
number display system. Tokens are distributed on ‘first come,
first serve’ basis and as soon as the service is ready for the
customer, the attendant has to just enter the token number
which will be displayed on a large seven segment display with
an alarm. The customer need not wait in the queue once their
order is placed. They can have a chat or ease, till their token
number is displayed and then can get their order.
Low power or Power down mode
Low power or power down mode is entered by executing
SLEEP instruction. The I/O ports maintain the status they had
before the SLEEP instruction was executed (driving high, low
or high-impedance). For lowest power consumption in this
mode, all the I/O ports are placed at either VDD or VSS,
ensuring that no external circuitry is drawing current from I/O
pin. The active low MCLR pin is kept at a logic level high.
The device wakes up from SLEEP through external input on
MCLR pin or PORTB change interrupt.
Keypad
In this system we use 4x3 matrix keypad which reduces
the I/O pin count to 7 which otherwise would be 12. Larger
keypads show an even greater efficiency.
The internal circuitry of a 4x3 keypad is as shown in Fig 2.
The four rows are read in via RB7:4 with internal pull-up
resistors enabled. The three columns connected to RB1:3 can
be individually selected in turn by driving the appropriate pin
low, thus scanning through the matrix. The switch contacts are
normally open and, because of the pull-up resistors, read as
logic 1. If a switch connected to a low column line is closed
then the appropriate row line is low. This means that once the
closed key row has been detected the column: row intersection
is known. The 330Ω resistors limit the current through the
switch.
74LS47-BCD to seven segment decoder/driver
The PIC microcontroller can be directly used to drive the
seven segment display. Due to the limited number of ports and
limited current output of PIC give rise to the need of driver
ICs. Another advantage of using the driver IC is that PIC can
be programmed to output the BCD of the number resulting in
interfacing two seven segment displays with PORTC and
PORTD. The BCD code of the number is sent to 74LS47
BCD to seven segment decoder/driver [2] which provides the
outputs that passes through appropriate segments to display
the decimal digit.74LS47 has 25mA sink current in open
collector configuration.
Fig 3. shows the BCD-to-7-Segment Decoder/Driver
(74LS47) being used to drive a 7-Segment common anode
LED readout. Each segment consists of one or two LEDs. The
anodes of the LEDs are all tied to Vcc (+5V/+12V). The
cathodes of the LEDs are connected through current–limiting
resistors to the appropriate outputs of the decoder/driver.
EXPERIMENTS AND RESULTS
The construction and implementation of the system was
carried out in different stages in order to obtain the expected
results. Overall system design was divided into modules
which were individually designed and tested before the
integration of the various subsystems. Software design was
started in MPLAB IDE. A series of program was written in
PIC assembly language. It was then compiled and simulated in
the MPLAB environment. The MPASM assembler (the
assembler) is a command-line or Windows-based PC
application that provides a platform for developing assembly
language code for Microchip's PIC microcontroller families.
The version we used was MPLAB IDE 7.3. After satisfactory
result was obtained the interactive simulation was carried out
in Proteus. This software is a revolutionary interactive system
level simulator developed by Labcenter Electronics. The
version we used was Proteus 6.9 SP5 with Advanced
Simulation.
WORKING OF THE SYSTEM
The number entered through the keypad is given as input
to the PIC microcontroller. The keypad is matrix 4x3
telephonic keypad. The microcontroller identifies the key with
the help of a keypad scanning algorithm described later in the
paper. Initially both the operator and customer displays are set
to 00. It sends the corresponding BCD equivalent of the
entered number to the 7447 BCD to seven segment
decoder/driver which drives the operator display. When the
‘BUZ’ key is pressed, the numbers in the operator display are
exhibited in the large customer display with a pleasant sound
indicating the availability of service. The system takes care of
the false triggering of sound system without entering token
number. If the system remains idle, that is, no number is
entered for a certain amount of time; the system enters the low
power mode. To resume, the system is reset. The power
supply unit provides the required power for the entire system.
CONCLUSION
This is a unique microcontroller based token number
display system which enters a low power state when kept idle
for certain amount of time, reducing power consumption
which is a great advantage in the times of energy crisis. This
system consists of a 4x3 telephonic keypad to enter the token
number which is identified by microcontroller and drives the
display driver which in open collector mode drives the large
seven segment display.