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Objective :
The purpose of this circuit is to operate the device that included
this circuit in a temporary period of time
Theory & background information :
A timer is a specialized type of clock. A timer can be used to
control the sequence of an event or process. Whereas a
stopwatch counts upwards from zero for measuring elapsed
time, a timer counts down from a specified time interval, like an
hourglass. Timers can be mechanical, electromechanical,
electronic (quartz), or even software as all computers include
digital timers of one kind or another.
Electronic timers can achieve higher precision than mechanical
timers because they are quartz clocks with special electronics.
Electronic timers can be analog (resembling a mechanical timer)
or digital (uses a display much like a digital clock). Integrated
circuits have made digital logic so inexpensive that an electronic
timer is now less expensive than many mechanical and
electromechanical timers. Individual timers are implemented as
a simple single-chip computer system, similar to a watch. Watch
technology is used in these devices.
A relay is an electrically operated switch. Many relays use an
electromagnet to operate a switching mechanism, but other
operating principles are also used. Relays find applications
where it is necessary to control a circuit by a low-power signal,
or where several circuits must be controlled by one signal.
The figure [1] that shows the relay.
The LM741 series are general purpose operational amplifiers it
is intended for a wide range of analog applications.
The high gain and wide range of operating voltage provide
superior performance in integrator, summing amplifier, and
general feedback applications.
A circuit model of an operational amplifier is shown in Figure 2.
The output voltage of the op amp is linearly proportional to the
voltage difference between the input terminals V+ ‫ـــ‬V- by a
factor of the gain A. However, the output voltage is limited to
the range –Vcc <= V <= Vcc , where Vcc is the supply voltage
specified by the designer of the op amp. The range –Vcc <= V
<= Vcc is often called the linear region of the amplifier, and
when the output swings to Vcc or -Vcc, the op amp is said to be
saturated. The output ranges of the amplifiers we built as part
of Lab 3 were similarly limited by the supply voltage.
Figure [1] : relay device
figure [2] : DIP pin out for 741-type operational amplifier
figure [3] : IC of lm741
The PNP Transistor is the exact opposite to the NPN
Transistor device we looked at in the previous tutorial.
Basically, in this type of transistor construction the two diodes
are reversed with respect to the NPN type, with the arrow,
which also defines the Emitter terminal this time pointing
inwards in the transistor symbol. Also, all the polarities are
reversed which means that PNP Transistors "sink" current as
opposed to the NPN transistor which "sources" current. Then,
PNP Transistors use a small output base current and a negative
base voltage to control a much larger emitter-collector current.
The construction of a PNP transistor consists of two P-type
semiconductor materials either side of the N-type material as
shown below.
The PNP Transistor has very similar characteristics to their
NPN bipolar cousins, except that the polarities (or biasing) of
the current and voltage directions are reversed for any one of the
possible three configurations looked at in the first tutorial,
Common Base, Common Emitter and Common Collector.
Generally, PNP Transistors require a negative (-ve) voltage at
their Collector terminal with the flow of current through the
emitter-collector terminals being Holes as opposed to Electrons
for the NPN types. Because the movement of holes across the
depletion layer tends to be slower than for electrons, PNP
transistors are generally slower than their equivalent NPN
counterparts when operating.
Application of timer circuit :
We have many application of this circuit, in any device we need
timer like this:
1) In computer device.
2) Mobile equipments.
3) In televisions.
4) Auto locks system in car.
5) Digital camera.
6) Automatic Washing machine.
7) Control device
8) Determine time for work any machine
Steps for connect this circuit:
 We must connect all component like this circuit
 Then we must use the data sheet for all component to
know the correct connections ,we must have circuit like
this :
 And after make test we must make calculation for time in
the rule
Vcc(t)=Vf(1-e^(-t/RC)) “when we make test we have
minimum time 10 mint and maximum time 3.30 hour”
 Then we must make test and make camper with the
calculation of time
 At the last after make test for all component and the
work we must make small box for this circuit like this :
Conclusion:
Good understanding for electronic pieces was achieved in this
project. Besides that, the way to design an appropriate cover was a
way to produce a nice and a practical shape in this work.
The main concept in this project is the time which organizing when
or -when not – lighting up the lamp and all that depend basically on
the capacitor used. In other meaning, the capacitor need’s a time to
be charged and that provide us ON period of light emitted from lamp
until the capacitor fully charged.
Reference for all information:
 http://www.national.com/analog
 http://category.alldatasheet.com/
 Electronic device and circuit theory -10 th edition
Philadelphia University
Engineering Faculty
Communication and Electronic Engineering
Department
Report of circuit project
“Timer”
Name of students group:
 Mohamed yamman fatal #200611313
 Abd al rahman rehawe #200611187
 Mustafa M-kullab #200610144

By:
Dr: Abdel-Rahman Al-Qawasmi