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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