The basic aim of the project is to design a compact user-friendly clock. It is digital in nature and
programmable.
This clock can sense temperature and
displays it on LED display. Also it displays date and time of the day.
It works on the Master Slave principle,
which has master clock and slave clock with their display, microcontroller and
temperature sensor mounted on PCB.
The project is divided into two parts:
·
Master clock
·
Slave clock
In Master clock -
A power supply is also made on the board
to convert the ac voltage into fixed regulated D.C. voltage to supply 5 volts
to all the IC’s and peripherals. In master clock there is one real time clock
IC is mounted on PCB.
In Slave clock -
In slave clock there is no real time
clock, but all the slaves have one temperature IC that is mounted on PCB
because temperature is different in other areas.
In today’s world, while dealing with
various electronics equipments and devices, it is desired to have visual
information. Various applications demand a display system to convey ‘Basic and
vital’ information to a large number of people.
In master slave clock, we are having one
master clock, which will control all other slaves.
Master accepts information from the
various peripherals and displays it on its own display and slaves accepts that
data and also displays it on their own display. This can be done through an
RS-485 cable for serial communication. The micro controller then sends the data
corresponding to the input to the display panel and it also synchronizes data
between master and slave clock.
On display panel displaying
parameters like temperature, date, time and also having one more feature of
ringing circuitry. Whenever we change time and date on master, the same change
will be on slaves.
using real time
clock IC for updating day and time in case of power failure. It updates data by
internal battery back.
In master slave clock, we can use up to
32 slaves by using RS-485 cable. But if we want to connect more slaves we can
connect them by using repeaters.
Microcontroller:
Pin no.31 is given to Vcc.
Pin no.18 and 19 are connected to the crystal
oscillator of frequency 11.0592 MHz.
Pin no.9 is connected to reset pin of real
time clock. Reset pin is used to reset the microcontroller in case the program
goes into an infinite loop or does not respond for particular amount of time.
When microcontroller is reset, then all the
counters and flags are brought to their original values.
Pin no.12 is INT0; the output from real time
clock (i.e. pin no.19) is given here.
Port P2.0-P2.4 is given to the driver; these
are the output digits from the microcontroller.
Port P0.0-P0.7 is given to real time clock IC
(i.e. from pin no.4 to 11) to send data.
Pin no.30 is given to real time clock to
latch the address.
Also RD, WR and RST pins of microcontroller
are given to real time clock IC.
These are the various connections of the
microcontroller (89S52) and real time clock IC
(DS12C887).
Ringing Circuit:
Pin no.15 of microcontroller i.e. timer1 is
connected to ringing circuit to make a ring for predetermined time.
RS-485:
IC 75176 is used in the circuit make
communication compatible between RS-485 and microcontroller. It is
bi-directional transceiver.
Pin no.1 and 4 are interfaced with
microcontroller.
Temperature Sensor:
Display:
Pin no.21, 22,23,24,25 are connected to the
digits 1,2,3, 4,5 respectively to the microcontroller output.
The other pins are the 7-digit output.
We use a linear power supply with a regulated IC 7805, which gives a
constant output voltage of +5volts. The transformer is step down transformer,
which converts 230V to 9V. Then the bridge rectifier rectifies the signal and
converts the ac signal to a positive wave. Then filter removes the ripples and
makes it a constant wave with reduced ripples. We used a capacitor filter which
charges when the wave goes positive from zero to max value. Then the capacitor
starts to discharge but has a very large discharge time and doesn’t get fully
discharged till the next high wave starts. Therefore it starts charging again
and the cycle repeats itself.
The regulated gives a ripple free
regulated output; the capacitors around the input and output are used to remove
noise. The diode provides short circuit protection as a high voltage if by
mistake passed on to the other devices could be very dangerous and could damage
all the devices connected to the power supply.
Fig 7:OUTPUT VOLTAGE OF REGULATOR
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The Bridge
Rectifier:
When four diodes are connected as shown
in figure, the circuit is called a BRIDGE RECTIFIER. The input to the circuit
is applied to the diagonally opposite corners of the network, and the output is
taken from the remaining two corners.
Fig 8. Bridge rectifier.
One complete cycle of operation will be
discussed to help you understand how this circuit works. We have discussed
transformers in previous modules in the NEETS series and will not go into their
characteristics at this time. Let us assume the transformer is working properly
and there is a positive potential at point A and a negative potential at point
B. The positive potential at point A will forward bias D3 and reverse bias D4.
The negative potential at point B will forward bias D1 and reverse bias D2. At
this time D3 and D1 are forward biased and will allow current flow to pass
through them; D4 and D2 are reverse biased and will block current flow. The path
for current flow is from point B through D1, up through RL, through
D3, through the secondary of the transformer back to point B. The solid arrows
indicate this path. Waveforms (1) and (2) can be observed across D1 and D3.
Filters:
While the output of a rectifier is a
pulsating dc, most electronic circuits require a substantially pure dc for
proper operation. Single or multisection filter circuits placed between the
output of the rectifier and the load provide this type of output.
There are
four basic types of filter circuits:
·
Simple capacitor filter
·
LC choke-input filter
·
LC capacitor-input filter
(pi-type)
·
RC capacitor-input filter
(pi-type)
Filtering is accomplished by the use of
capacitors, inductors, and /or resistors in various combinations. Inductors are
used as series impedances to oppose the flow of alternating (pulsating dc)
current. Capacitors are used as shunt elements to bypass the alternating
components of the signal around the load (to ground). Resistors are used in
place of inductors in low current applications.
Lets
briefly review the properties of a capacitor. First, a capacitor opposes any
change in voltage. The opposition to a change in current is called capacitive
reactance (Xc) and is measured in ohms. The capacitive reactance is determined
by the frequency (f) of the applied voltage and the capacitance (C) of the
capacitor.
if frequency or capacitance is increased, the Xc
decreases. Since filter capacitors are placed in parallel with the load, a low
Xc will provide better filtering than a high Xc. For this to be accomplished, a
better shunting effect of the ac around the load is provided, as shown in fig.
To obtain a steady dc output, the capacitor must charge almost instantaneously
to the value of applied voltage. Once charged, the capacitor must retain the
charge as long as possible. The capacitor must have a short charge time
constant (view A). This can be accomplished by keeping the internal resistance
of the power supply as small as possible (fast charge time) and the resistance
of the load as large as possible (for a slow discharge time a illustrated in
view B).
The Capacitor Filter:
The simple capacitor filter is the most
basic type of power supply filter. The application of the simple capacitor
filter is very limited. It is sometimes used on extremely high-voltage,
low-current power supplies for cathode ray and similar electron tubes, which
require very little load current from the supply. The capacitor filter is also
used where the power-supply ripple frequency is not critical; this frequency
can be relatively high. The capacitor (C1) shown in figure is a simple filter
connected across the output of the rectifier in parallel with the load.
.
When this filter is used, the RC charge
time of the filter capacitor (C1) must be short and the RC discharge time must
be long to eliminate ripple action. In other words, the capacitor must charge
up fast, preferably with no discharge at all. Better filtering also results
when the input frequency is high; therefore, the full-wave rectifier output is
easier to filter than that of the half-wave rectifier because of its higher
frequency.
Current pulses flow through the load
resistance (RL) each time a diode conducts. The dashed line
indicates the average value of output voltage. For the half-wave rectifier, Eavg
is less than half (or approximately 0.318) of the peak output voltage. This
value is still much less than that of the applied voltage. With no capacitor
connected across the output of the rectifier circuit, the waveform in view A
has a large pulsating component (ripple) compared with the average or dc
component. When a capacitor is connected across the output (view B), the
average value of output voltage (Eavg) is increased due to the
filtering action of capacitor C1.
The value of the capacitor is fairly
large (several microfarads), thus it presents a relatively low reactance to the
pulsating current and it stores a substantial charge.
5.2 LM 7805:
Description:
The LM78XX
series of three terminal positive voltage regulators is available with several
fixed output voltages making them useful in a wide range of applications. One
of these is local on card regulation, eliminating the distribution problems
associated with single point regulation. The voltages available allow these
regulators to be used in logic systems, instrumentation, Hi-Fi, and other
solid-state electronic equipment. Although designed primarily as fixed voltage
regulators these devices can be used with external components to obtain
adjustable voltages and currents.
The LM78XX series is available in an
aluminum TO-3 package that will allow over 1.0A load current if adequate heat
sinking is provided. Current limiting is included to limit the peak output
current to a safe value. Safe area protection for the output transistor is
provided to limit internal power dissipation. If internal power dissipation
becomes too high for the heat sinking provided, the thermal shutdown circuit
takes over preventing the IC from overheating. Considerable effort was expanded
to make the LM78XX series of regulators easy to use and minimize the number of
external components. It is not necessary to bypass the output, although this
does improve transient response. Input bypassing is needed only if the
regulator is located far from the filter capacitor of the power supply. For
output voltage other than 5V, 12V and 15V the LM117 series provides an output
voltage range from 1.2V to 57V.
Features:
·
Output current in excess of 1A
·
Internal thermal overload protection
·
No
external components required
·
Output transistor safe area protection
·
Internal short circuit current limit
·
Available in the aluminum TO-3 package
·
Output voltages of 5V, 12V and 15V.
Fig
11: Microcontroller IC
The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller that provides a highly flexible and cost-effective solution to many embedded control applications.
Features:
• Compatible with
MCS-51 Products
• 8K Bytes of
In-System Programmable (ISP) Flash Memory
Endurance: 1000 Write/Erase Cycles
• Fully Static
Operation
• 256 x 8-bit
Internal RAM
• 32 Programmable I/O
Lines
• Three 16-bit
Timer/Counters
• Eight Interrupt
Sources
• Speed up to 33 MHz
Working:
We use port
2 for the output connected to the driver circuit and then to the seven-segment
display. The other port we use is the port 0 for address data signals. The INT0
pin sends an interrupt signal to the microcontroller whenever an input signal
has to display. This interrupt starts the microcontroller program that updates
the data for one second and stores the value in registers. A delay of 1 second
is used in which the microcontroller counts the number of high to low
transitions using an increasing 16-bit counter. The output of the counter is
stored in a 16-bit register. This value in register is then send to the I/O
port 2 as output.
The microcontroller is also programmed
to give temperature of the atmosphere, which is given to display. The program
is written to display this temperature after some amount of delay using delay
function. Every time an input from various peripherals is given to the
microcontroller, then program starts running and displayed on display panel.
These are the various
functions of the microcontroller.
Theory:
The
microcontroller has 40 pins. 32 are input-output pins and the remaining 8
perform various functions like reset, reference voltage oscillator input and
ground.
It has 4 ports each port contains 8 pins.
Port 0:
Port 0 is an
8-bit open drain bi-directional I/O port. The 8 pins can also be used as
multiplexed address and data bus. It stores the lower 8 bits of the address
bus.
Port 1:
It is a basic input-output port with no
other special feature. Used for parallel communication with any parallel
device.
Port 2:
It is like
port 0. it is used for the next 8 bits of the address bus to extend the memory.
Port 3:
It is a
special bus can be used for basic I/O operations as well as for serial data
transmission. This port is also used for some special functions like interrupts,
timers, read and write operations.
Memory Organization:
MCS-51 devices have a separate address
space for Program and Data Memory. Up to 64K bytes each of external Program and
Data Memory can be addressed.
Program Memory:
If the EA pin is connected to GND, all
program fetches are directed to external memory. On the AT89S52, if EA is
connected to VCC, program fetches to addresses 0000H through 1FFFH are directed
to internal memory and fetches to addresses 2000H through FFFFH are to external
memory.
Data Memory:
The AT89S52 implements 256 bytes of
on-chip RAM. The upper 128 bytes occupy a parallel address space to the Special
Function Registers. This means that the upper 128 bytes have the same addresses
as the SFR space but are physically separate from SFR space.
DESCRIPTION:
The DS1621 Digital Thermometer and
Thermostat provides 9–bit temperature readings, which indicate the temperature
of the device. The thermal alarm output, TOUT, is active when the temperature
of the device exceeds a user–defined temperature TH. The output remains active
until the temperature drops below user defined temperature TL, allowing for any
hysteresis necessary. User-defined temperature settings are stored in
nonvolatile memory so parts may be programmed prior to insertion in a system.
Temperature settings and temperature readings are all communicated to/from the
DS1621 over a simple two–wire serial interface.
FEATURES:
- Temperature measurements require no external components.
- Measures temperatures from –55°C to +125°C in 0.5°C increments. Fahrenheit
equivalent is –67°F to 257°F in
0.9°F increments.
3.
Temperature is read as a 9–bit value (2-byte transfer)
- Wide power supply range (2.7V to 5.5V)
- Converts temperature to digital word in 1 second.
- Thermostatic settings are user definable and nonvolatile.
7.
Data is read from/written via a two–wire serial interface (open drain
I/O lines)
The DS12C887 Real Time Clock plus RAM is
designed as a direct upgrade replacement for the DS12887 in existing IBM
compatible personal computers to add hardware year 2000 compliance. A century
byte was added to memory location 50, 32h, as called out by the PC AT
specification. A lithium energy source, quartz crystal, and write-protection
circuitry are contained within a 24–pin dual in-line package. As such, the
DS12C887 is a complete subsystem replacing 16 components in a typical
application. The functions include a nonvolatile time-of-day clock, an alarm, a
one-hundred-year calendar, programmable interrupt, square wave generator, and
113 bytes of nonvolatile static RAM. The real time clock is distinctive in that
time-of-day and memory are maintained even in the absence of power.
FEATURES:
- Totally nonvolatile with over 10 years of operation in the absence of power.
- Self-contained subsystem includes lithium, quartz, and support circuitry.
- Counts seconds, minutes, hours, days, day of the week, date, month, and year with leap year compensation valid up to 2100.
- Binary or BCD representation of time, calendar, and alarm.
- 12– or 24–hour clock with AM and PM in 12-hour mode.
- Daylight Savings Time option.
- Multiplex bus for pin efficiency.
- Interfaced with software as 128 RAM locations and 113 bytes of general purpose RAM.
- 15 bytes of clock and control registers and century register.
- 113 bytes of general purpose RAM.
- Bus–compatible interrupt signals (IRQ).
- Three interrupts are separately software maskable and testable
- Time–of–day alarm once/second to once/day
In the project, communication from PC to
master clock is done with DS232A and to connect number of slaves to the master
we are using RS-485. The DS232A is a dual RS-232 driver/receiver pair that
generates RS-232 voltage levels from a single +5 volt power supply. Additional
±12 volt supplies are not needed since the DS232A uses on-board charge pumps to
convert the +5 volt supply to ±10 volts.
Standards have been developed to insure
compatibility between units provided by different manufacturers, and to allow
for reasonable success in transferring data over specified distances and/or
data rates. The Electronics Industry Association (EIA) has produced standards
for RS-485, RS-422, RS-232 and RS-423 that deal with data communications.
Selection of RS-485
depends upon number of conductors, shielding and cable characteristics.
Table
1: Specifications
|
SPECIFICATIONS
|
RS232
|
RS423
|
RS422
|
RS485
|
|
|
Mode of Operation
|
SINGLE
-ENDED |
SINGLE
-ENDED |
DIFFERENTIAL
|
DIFFERENTIAL
|
|
|
Total Number of Drivers and Receivers on One Line
(One driver active at a time for RS485 networks)
|
1
DRIVER
1 RECVR |
1
DRIVER
10 RECVR |
1
DRIVER
10 RECVR |
32
DRIVER
32 RECVR |
|
|
Maximum Cable Length
|
50
FT.
|
4000
FT.
|
4000
FT.
|
4000
FT.
|
|
|
Maximum Data Rate (40ft. - 4000ft. for RS422/RS485)
|
20kb/s
|
100kb/s
|
10Mb/s-100Kb/s
|
10Mb/s-100Kb/s
|
|
|
Maximum Driver Output Voltage
|
+/-25V
|
+/-6V
|
-0.25V
to +6V
|
-7V
to +12V
|
|
|
Driver Output Signal Level (Loaded Min.)
|
Loaded
|
+/-5V
to +/-15V
|
+/-3.6V
|
+/-2.0V
|
+/-1.5V
|
|
Driver Output Signal Level (Unloaded Max)
|
Unloaded
|
+/-25V
|
+/-6V
|
+/-6V
|
+/-6V
|
|
Driver Load Impedance (Ohms)
|
3k
to 7k
|
>=450
|
100
|
54
|
|
|
Max. Driver Current in High Z State
|
Power On
|
N/A
|
N/A
|
N/A
|
+/-100uA
|
|
Max. Driver Current in High Z State
|
Power Off
|
+/-6mA
@ +/-2v
|
+/-100uA
|
+/-100uA
|
+/-100uA
|
|
Slew Rate (Max.)
|
30V/uS
|
Adjustable
|
N/A
|
N/A
|
|
|
Receiver Input Voltage Range
|
+/-15V
|
+/-12V
|
-10V
to +10V
|
-7V
to +12V
|
|
|
Receiver Input Sensitivity
|
+/-3V
|
+/-200mV
|
+/-200mV
|
+/-200mV
|
|
|
Receiver Input Resistance (Ohms), (1 Standard Load
for RS485)
|
3k
to 7k
|
4k
min.
|
4k
min.
|
>=12k
|
|
Pin no.15 of microcontroller i.e. timer1 is connected to ringing circuit
to make a ring for predetermined time. This ringing circuitry will be useful
for ringing at the time of start and end of college, for recess time.
involve single
crystal phosphor materials, which distinguishes them from the polycrystalline
electro luminescent displays. Light emitting diodes (LED) are PN junction
devices that give off light radiation when biased in the forward direction.
Most light emitting diodes function in the near infrared and visible
ranges, though there are now UV LEDs. Light emitting diodes are a reliable
means of indication compared to light sources such as incandescent and neon
lamps. LEDs are solid-state devices requiring little power and generating
little heat. Because their heat generation is low and because they do not rely
on a deteriorating material to generate light, LEDs have long operating
lifetimes. One of the alternatives, incandescent bulbs, consumes much more
power, generate a great deal of heat, and rely on a filament that deteriorates
in use. Neon bulbs, on the other hand, rely on excited plasma, which, along
with its electrodes, can deteriorate over time. LED displays,
digital, are highly versatile and well suited to a variety of measurement
applications. Display types can be segmented or dot matrix. A
seven-segment display can display numbers only; a sixteen-segment display can
display numbers and letters. A 4x7 dot matrix display can display numbers
only; a 5x7 dot matrix display can display numbers and letters. LED
displays, digital can be numeric or alpha numeric. Numeric displays
display numbers only, a seven-segment display or 4x7 dot matrix display.
An alphanumeric display can display numbers and letters, a sixteen-segment
display or 5x7 dot matrix display.
LED displays can have a common anode or
common cathode configuration. In a common anode configuration all the
segments in the LED share one anode pin. In a common cathode
configuration all the segments in the LED share one cathode pin. Common
cathode is the "standard" circuit where the cathode is connected to
the "common" point on the circuit, usually ground, and usually
through a resistor, which is often bypassed with a capacitor, placing it at
"AC" ground potential. Important display package specifications
to consider when searching for LED displays, digital include the number of rows
and the number of characters per row. Standard color choices for LEDs
include standard red, yellow, high efficiency red, orange, green, and
blue. Other display specifications to consider include color wavelength,
character height, and viewing distance. Wavelength of the display will be
determined by the color of the LED. Viewing distance is determined
primarily by the minimum size requirements for objects that the user must
see. The viewing angles on the x and y-axis are also important to
consider. The viewing angle of the display is the angle, in degrees,
between a line normal to the display surface and the user's visual axis.
Minimum and typical luminous intensity describe the luminous flux per unit
solid angle, and its unit of measurement is the candela (cd). Case
dimensions include width depth and height. The case or package of the
display will have separate dimensions than the actual viewing area of the
display.
LED displays, message, are
typically commercial or industrial signs. They allow for larger characters and
longer viewing distances than digital LED displays. Light-emitting diode (LED)
displays are segmented or dot matrix displays allowing for numeric only and
alphanumeric character representation. Light emitting diodes (LED)
are PN junction devices that give off light radiation when biased in the
forward direction. Most light emitting diodes function in the near
infrared and visible ranges, though there are now UV LEDs. Light emitting
diodes are a reliable means of indication compared to light sources such
as incandescent and neon lamps. LEDs are solid-state devices requiring little
power and generating little heat. Because their heat generation is low and
because they do not rely on a deteriorating material to generate light, LEDs
have long operating lifetimes. One of the alternatives, incandescent bulbs,
consumes much more power, generate a great deal of heat, and rely on a filament
that deteriorates in use. Neon bulbs, on the other hand, rely on excited
plasma, which, along with its electrodes, can deteriorate over time.
Choices for display types for LED displays, message; include matrix, line, character, fixed digit, and ticker. A matrix display is composed of an array of LEDs able to form graphics. A line display only displays messages in a line format. A character display is composed of an array of LEDs only capable of displaying characters. On a fixed digit display the digits are fixed and cannot move. On a ticker display the digits can move across the viewing area. LED displays, message can be configured to be used in either an indoor application or an outdoor application. Displays that are configured for outdoors use have weatherproof housings.
Choices for display types for LED displays, message; include matrix, line, character, fixed digit, and ticker. A matrix display is composed of an array of LEDs able to form graphics. A line display only displays messages in a line format. A character display is composed of an array of LEDs only capable of displaying characters. On a fixed digit display the digits are fixed and cannot move. On a ticker display the digits can move across the viewing area. LED displays, message can be configured to be used in either an indoor application or an outdoor application. Displays that are configured for outdoors use have weatherproof housings.
Important configuration parameters to consider when specifying LED displays, message, include character height, number of lines, number of characters, viewing distance, viewing angle, and luminous intensity. The character height may also be called pitch. The number of lines will determine the size of the message display. The number of characters refers to the number of characters per line. Viewing distance is determined primarily by the minimum size requirements for objects that the user must see. The viewing angle is the angle, in degrees, between a line normal to the display surface and the user's visual axis. Luminous intensity is typically given @ 10mA. Also known as pixel brightness. Luminous intensity is luminous flux per unit solid angle, and its unit of measurement is the candela (cd).
LED displays, message, can be mounted in a panel or case, or top mounted, or bottom mounted. Top mounted displays can hang from the ceiling. Case dimensions of height, width, and depth are important to consider. Common features include special effects or animations, programmability, selectable fonts, displaying of countdown time, adjustable intensity, and clock format. Special effects include a variety of scrolling, wiping, twinkling, flashing, images and animations that function in conjunction with text or as stand-alone effects. They are used to provide emphasis on specific textual statements, to simply draw attention to the display, or to provide an additional level of entertainment in conjunction with message presentation. Important environmental parameters to consider when specifying LED displays, message include operating humidity and operating temperature.
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