We have implemented a real time switch
which will allow the user to put on/off his circuitry according to his
requirement. In almost every industry, household appliances, agricultural
activities, the use of this system proves advantageous. In this project the
user needs to enter the on time and the off time. hence the micro-controller
will automatically switch on and off accordingly. if the power is disconnected,
the entered data need not to be re-entered. if the power is disconnected
between the on-off time, the micro-controller will switch on the output
circuitry immediately after the power is supplied…this feature is important in
case of electrical devices which requires starters such as motors, actuators
etc. as this whole circuitry works as a switch which operates on real time (24hrs/12hrs)
hence it is named as real time switch. Thus this project will help in
automation of industries, agricultural activities and home appliances and hence
will reduce the efforts.
Specifications
Circuit specifications
·
It
displays 24 hours clock on switching on the circuit.
·
It
allows the user to enter the switch on time and the switch off time.
Electrical specifications
·
IC’s rtc-ds1307 operates on +5volts supply and
+3.5volts battery backup, at89c51 operates on +5 volts
·
relay
used operates on 5 volts and is normally open in nature.
·
transformer
ratings are:
·
230
volts primary.
·
9
volts secondary.
·
1.5
A current capacity.
·
25:1
turns ratio.
I/O specifications
·
input:
real time (on and off time)
·
output:
7-segment clock display and lamp through relay.
There are six main blocks which play
an important role in performing the operation. The blocks are as follows-
·
Microcontroller.
·
Real
time clock (rtc).
·
Input
switches
·
Seven
segment display
·
Power
supply circuit
·
Relay
driver circuit.
Microcontroller
This is the brain of the whole system
which controls and gives commands to the rtc and the other circuitry. it will
switch on &off the output relay circuitry according to requirement of user.
it will also display current time on 7-segment display. Here we are using
at89c51 microcontroller which is compatible with intel 8051 instruction set. The
microcontroller will generate the at commands, which are required by the user
to monitor the system. It will also check the status of the rtc and take the
decisions accordingly. the communication between microcontroller and computer
is through serial communication.
Real
time clock
It is the ic which gives 12/24 hrs
clock output to the microcontroller so that microcontroller can operate on this
time. Here we are using rtc-ds1307 manufactured by dallas semiconductors. Real
time clock counts seconds, minutes ,
hours, date of the month, month, day of the week, and year with leap year
compensation valid up to 2100.it has56 byte nonvolatile ram for data storage .
Operation
The ds1307 operates as a slave device
on the serial bus. Access is obtained by implementing a start condition and
providing a device identification code followed by a register address. Subsequent
registers can be accessed sequentially until a stop condition is executed. When
vcc falls below 1.25 x vbat the device terminates an access in progress and
resets the device address counter. Inputs to the device will not be recognized
at this time to prevent erroneous data from being written to the device from an
out of tolerance system. When vcc falls below vbat the device switches into a
low current battery backup mode. Upon power up, the device switches from
battery to vcc when vcc is greater than vbat +0.2v and recognizes inputs when
vcc is greater than 1.25 x vbat. the block diagram in figure 1 shows the main elements
of the serial real time clock.
Power
supply
The voltage required to operate is +5v
(regulated). The regulated +5v is generated using ic7805. the input for this
regulator ic is rectified and the filters from full wave rectifier and
capacitor filter. The output is obtained and is given to the microcontroller
and the sensors.
Input
switches
Here we have used five input switches
as
·
time
set switch
·
on
time switch
·
off
time switch
·
hours
adjust switch
·
minutes
adjust switch
We have used push buttons here.
7-segment
display
In the circuit, we are using common
anode type 7-segment display with a driver ic uln2803 which will make 7-segment
display compatible with microcontroller output.
Relay
driver section
The relay driver circuit is build up
to get the output. A 12volt relay along with a output lamp forms the output
part. This lamp glows in the time span given by the user i.e it gets on at the
on time and gets off when off time is reached.
modulewise description
·
The
block diagram of the real time switch can be classified as follows
·
There
are 6 main blocks in the system
·
Microcontroller
section
·
rtc
section
·
Input
switches section
·
Seven
segment display section
·
Relay
driver section
·
Software
section
·
Power
supply section
Microcontroller
section
Starting with the crystal which has the
clock frequency of 11.0592 mhz has been used along with the capacitor of 33pf.
the crystal generates the clock pulses which are fed directly to the pins 18
and 19. Capacitor c of 10µf and the resistance r of 10kΩ are used to reset the
microcontroller by pressing the switch connected in parallel with the
capacitor. So baud rate of microcontroller is 9600. rtc is interfaced to
microcontroller using wires.scl and sda pins of rtc are connected to port pins
26 and 25 respectively. Microcontroller initiates rtc and make it work. the
data from rtc memory is accessed using i2c bus protocols. Switches are
connected to port1 of microcontroller. Common anode seven segment display is
interfaced to port0 of controller. thus we are getting output at port pin 27
i.e. we have connected relay circuit at this pin. Microcontroller is
continuously accessing current time from rtc & displaying it on 7-segments.
It is controlling relay circuitry according to on/off times entered through
switches.
rtc
section
ic ds1307 is a real time clock. It is
a 6 pin ic. The ds1307 serial real time clock is a low power, full bcd
clock/calendar plus 56 bytes of nonvolatile SRAM. Address and data are
transferred serially via a 2-wire bi-directional bus. The clock/calendar
provides seconds, minutes, hours, day, date, month, and year information. the
end of the month date is automatically adjusted for months with less than 31
days, including corrections for leap year. the clock operates in either the
24-hour or 12-hour format with am/pm indicator. the ds1307 has a built-in power
sense circuit which detects power failures and automatically switches to the
battery supply. When vcc falls below vbat the device switches into a low
current battery backup mode. upon power up, the device switches from battery to
vcc when vcc is greater than vbat +0.2v and recognizes inputs when vcc is
greater than 1.25 x vbat.
scl (serial clock input) - scl is used
to synchronize data movement on the serial interface. sda
(serial data input/output) - sda is the input/output pin for the 2-wire serial
interface. the sda pin is open drain which requires an external pull-up
resistor.
Clock
and calendar
The time and calendar information is
obtained by reading the appropriate register bytes. The time and calendar are
set or initialized by writing the appropriate register bytes. The contents of
the time and calendar registers are in the binary-coded decimal (bcd) format. Bit
7 of register 0 is the clock halt (ch) bit. When this bit is set to a 1, the
oscillator is disabled. When cleared to a 0, the oscillator is enabled.
Inputs
switch section
Using this section the user can enter
the span to get the output from the relay driver circuit.the operation of the
switches is illustrated below.
Time set switch
This switch is required to set the current
time initially.
On time switch
By using this switch the user can
enter his on time. For this purpose this switch has to be pressed and the time
is then set by adjusting the hours and mins switch.
Off time switch
By using this switch the user can
enter his off time. for this purpose this switch has to be pressed and the time
is then set by adjusting the hours and mins switch.
Hours adjust switch
This switch is used to adjust the
hours in the time displayed .by pressing this switch once the hours get
incremented by one and this is the only way to set the hours.
Minutes adjust switch
This switch is used to adjust the mins
in the time displayed. By pressing this switch once the mins get incremented by
one and this is the only way to set the mins.
Seven
segment display section
The four seven segments used will
display the real time clock in 24hr format with hours and mins. on pressing the
respective switches it will display the data associated with it. For example if
we press the on time switch then it will display the on time given by the
user.
Software
section
The i2c bus protocol:
The i2c bus physically consists of 2
active wires and a ground connection. The active wires, called sda and scl both
are bi-directional. sda is serial data line and scl is serial clock line. Every
device hooked up to the bus has its own unique address, no matter whether it is
an mcu, lcd driver, memory, or asic. Each of these chips can act as a receiver
and/or transmitter depending upon functionality. Obviously an lcd driver is
only a receiver, while a memory or i/o chip can be both transmitter and
receiver. The i2c is a multi master bus. This means that more than one ic
capable of initiating a data transfer can be connected to it. The i2c
specifications state that the ic that initiates data transfer on the bus is
considered as bus master. Consequently, at that time, all other ics are
referenced as bus slaves.
Relay
driver section
Using a relay driver circuit since it
acts as a switch. So to demonstrate the real time switch we have put a lamp
with the relay driver circuit as the load. This lamp will glow only in the time
duration given by the user .by using relay driver circuit input and output
circuits are isolated. it allows to drive a higher voltage load with a lower
voltage at the relay input.
Power
supply section
Designing a +5volt power supply using
9:0:9 step down transformer and regulator ic 7805.this +5 volt supply is then
given to all the blocks of the circuit.
Algorithm
Start
Accept time, day and date from r.t.c.
Read time.
Display the current time
Compare the r.t.c time with the on/off
time entered through switches
if time
does not match then return to the program and check it again and again. If time matches, switch on/off relay circuit.
Display the time
Display regular clock
Return to start.
End
Applications
of the system
Agriculture sector to reduce man
efforts and time
The institutes like colleges and
companies to operate lights, fans, acs, alarms at working time
Home appliances
Manufacturing industry i
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