Test Timer Prototype Product - Lab Report Example

Test Timer Prototype Product By Engineering and Construction of A timer has many applications in the electrical and electronic field. It can be used to delay electrical signals for a predetermined period of time. Most electrical circuits use timers to perform automated functions. This report documents design of a test timersystem. The stages are followed describing how each module of the timer is designed from the initial stages to achieve the final instrument. Several considerations in the design have been put in place for instance the price value of the components to ensure the cheapest design possible. Similarly, the best combinations for the circuits and instruments is used to achieve the simplest and most efficient timer. Chapter 1: Introduction/Objectives and Literature survey In this report the test timer has been implemented following a set of three major stages, implementing an amplifier unit, design and test of adelay unit and, design and test of an oscillator unit.Once each module has been completed, the final project is developed by joining each of the modules together and calibrating the final timer unit to fit the expected standards. Calibrating integrates all the three parts into one single entity that runs as an electrical timer. The major entities of the timer include a trigger which initiates the signal. The trigger signal is received by the adjustable delay unit which determines the amount of delay time required to ensure synchronization with the expected output. Once the signal has been delayed for the expected time, it is picked up by the audio signal generator which runs the oscillator to produce sound. The sound is directed to the amplifier to increase its frequency and output produced through the loud speaker as sound within a frequency range of 20 to 200kilo hertz. Chapter 2: Design and methodology The various devices are required in the implementation of this project. This include a simple resistor-capacitor (R-C), 555 based circuits, charged coupled devices (CCDs), shift registers and counters.A simple resistor-capacitor includes a capacitor and a resistor connected in series. It can be used to delay the signals by varying the amount of voltage stored in the combination. Inorder to increase the delay time, one needs to increase the flow rate by reducing the size of the voltage that can be stored in the combination. The combination has a range of 0 volts to 5 volts (INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS et al, 2001). There are a number of problems that limit its full functionality. Often they produce a poor waveform of voltage against time hence the signal results in a poor control of the delay which makes it not very reliable. The charged couple devices are mostly used in digital systems. They however are complicated to operate and have different voltage supply levels. They are also prone to charge injection work Problems: Complicated operation. They are used to control circuits for charge transfer. The shift register is used to record the changes in the signals for every stage. For each pulse, the shift register records a shift in the signal for one stage. It however, requires a clock generator to work and often posse difficulty when adjusting the delay time.The counters operate by shifting the signal for every digit at a difference of 2n (n=1, 2,…) pulses (STOREY, 2004).They also require a clock generator and a control circuit. The 555 based circuits are designed based on the resistor capacitor principle and produce a sharp response signal. They are also cheap which makes them suitable for use. The RS 555 chip would thus be used as the best solution for the delay unit design because it is cheap and has low power consumption. Figure 1:555 based circuit structure LMC555 chips are used with the 55 based circuits because they use a less power often less than 1mW dissipation of power. Its price range is about 45p to 99p. Figure 2: Low power CMOS chips. Design and test for the amplifier The amplifier required in this context has to sustain a large input signal. It requires at least a 0.7 voltage to turn on the transistor. In this design the input equals the output of the oscillator when the transistor is on. In this design there is no need for resistor 1 and 2 as well as capacitor 1.A small input signal will require more resistors and capacitors to help transform the voltage to produce a significant result. The figure shows a comparison between the amplifier circuit for a small input signal and a large input signal. Design and test for oscillator Sound is produced by the audio signal generators which use oscillators to produce sound. In order to produce sound an alternating current is needed since it is capable of producing vibrations in the circuit. The signal has to be in the range of about 20 Hz to 200 KHz, a frequency that the human ear can decipher. The oscillators are triggered by the output of the delay unit and generate AC signals. There are a number of oscillators which can be used in the development of an audio signal generator. They include an inductor-capacitor and a ring oscillator. For this project a ring oscillator was used since its design is based on the 555 circuit design. Some types are designed to use either, the NAND gate, NOR gate or are designed to be operational based circuits. NOR based oscillators are used in this project due to their ability to save cost and reduce the number of components needed.An NOR based oscillator runs on three variables Y, a and b. The current through a and b determines the output Y (DENTON, 2012). The logical reasoning behind it is that when a=1, then y=1 independent of b and similarly if b=1 when y=1 when independent of a. Thus y=0 only if a=b=0. NOR is used as an inverter. When Va=0,Vb=1, Vc=0, thus ‘C’ is charged through R by Vb. When Va reaches 1, Vb= 0 hence discharging c through R. This cycle repeats itself creating an oscillation. The frequency is determined by the magnitude of the signal received from the delay unit. The higher the magnitude (RC) the lower the frequency. The choice of the resistor and capacitor has to meet certain conditions. The RC has to have a range of between 20Hz to 200KHz. If R=100K, then P has to be less thanVcc2/R=0.81mW and C can be calculated by C=10-3/105=10-8F=10nF. C will store some power during the initial stages which fills up to a certain level. This will maintain the circuit in a steady condition for a smooth output. The alternating discharging by Va and Vb continuously results in an oscillation producing a constant repeating sound. Using the 555 based requires two chips (LMC555CN)which costs a total of 90p.Using the CD4001BCM chip gives 4 NORs and has the two oscillators on the same chip. This saves 70p for every unit. The first oscillator generates the signal while the second oscillator modulates the frequency (DENTON, 2012). Interfacing the amplifier requires using 6 resistance which is in range of the output signal from the delay unit and can be used to generate sound at a frequency that can be heard. A higher resistance would make the frequency of the sound be lower than expected which cannot be heard (DENTON, 2012). Delay Unit Calibration Once the product has been designed and meets the required objectives, there is need for calibration. This allows to make the product specific for use in different scenarios. Furthermore, to achieve the required resistance, more than one resistor is required. This helps in quality control of the timer instrument. Quality control can be achieved by varying the values of resistors and the capacitors (STOREY, 2004). This often is time consuming but has to be done to achieve the best results. Changing the potential at pin 5 for instance by increasing the voltage increases the delay while reducing it reduces the delay. Chapter 3: Results The signal generated from the trigger circuit shows a smooth curve that rises steadilywhich denotes a continuous signal. This shows a constant increase in the voltage which is expected from the timer. From the delay unit, once the timer has been adjusted, the final results show a sharp wave form that indicates immediate response. This is only possible after calibration of the instrument to ensure quality control of the output within the expected time range. The wavelength for Vc for the NOR gate based oscillator is significantly different form the wave form of Vout. The Vc NOR gate based produces a sharp waveform which is required for triggering the alarm at the expected time without errors. Thus using Vout would produce more errors and make it hard to calibrate the timer in general. The waveforms differ since an NOR gate allows the voltage to move through a resistor and capacitor circuit that quickly drains the voltage over a short period of time thus generating a sharp signal (DENTON, 2012). The other signal takes some time to drain the voltage from the power tank hence the continuous interface. The duration for Vout high and low changes over a short period of time of about three seconds which subsequently generates a signal interpreted as sound by the loudspeaker output. Chapter 4: Discussion From figure 3, when the switch is on, the time is initially zero and this triggers the value of pin 2 if it is less than Vcc divided by 3. The value of R=1, Q=1, and Q=0 at time t = 0. Thus C is charged through R when T1 is turned off. When Vc=2Vcc/3, S=1, Q=1 and Q=0. Turning on T1 shorts C and Vc=0. Figure 3: Delay Unit Connection In this design the maximum delay expected is 300s. R is chosen as the variable for adjusting the delay. Selecting R and C is based on various practical concepts. For instance a larger R implies a smaller Current and thus the potential for leakages is greatly reduced. Max R=300/C=3M.From the design of the trigger circuit, the value of pin 2 must be less than a third of Vcc and should rise above a third of Vcc when time t is far much less than W to allow for resetting the system. Pin 2 is connected to C1 thus V(C1) cannot change instantaneously. At t=0, V(C1)=0. The expected delay is less than 1 second. C1 discharges through R1 after switch off. R1 =R2 to make fabrication and buying in quantity easier. Figure 4:Design of trigger circuit. Chapter 5: Product specification/documentation The test timer is constructed using the 555 based circuit structure. It also incorporates the LCM555 CMOS chips on the circuit board. The output comes from a 65 ohm loud speaker. In order to operate the timer, an AC power source is needed. Plug the mains cable into the power source and switch it on. This immediately powers up the machine. An input value is expected. The user is required to enter a value in seconds of the time the timer should run before it triggers an alarm (DARR, 2004). Switch it off in case it is not in use to conserve power. Using the timer requires that the power supply is protected from power surges and unstable electrical connections.Interfacing the system can be done in a customized environment for various different applications especial in commercial applications. Figure 5: Circuit Diagram for the test timer Chapter 6: Conclusion and future works Timers can be used in the wide electrical fields. Most applications require customized designs to run on their systems. This design is a simple timer that allows one to enter a specified value. A counter is generated electronically using resistors and capacitors that read the time taken for an input voltage to change by a given value. Once the expected change occurs the timer uses oscillators to generate a monologue sound as an output to alert the user (CARELSE, 2001). This timer can be used in electrical instruments to generatecustomized signals for running control systems. The input can be fetched from measurements done using instruments connected to the control system hence making it an efficient the application in fields such as industrial automation. Future works are currently underway to develop timers that use less resistors and capacitors. Such systems willinclude microprocessors which can generate multiple signals to the timers at different intervals. Advanced control systems using such timers are necessary especially in fields such as robotics and artificial intelligence. References CARELSE, X. F. (2001). The design of solid state RC timers. Leatherhead, Electrical Research Association. DARR, J. (2004). The home appliance clinic: controls, cycle timers, wiring & repair. Blue Ridge Summit, Pa, Tab Books. DENTON, T. (2012). Automobile electrical and electronic systems: automotive technology : vehicle maintenance and repair. New York, Routledge. INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, IEEE COMPUTER SOCIETY, & IEEE-SA STANDARDS BOARD. (2001). IEEE standard for standard delay format (SDF) for the electronic design process. New York, N.Y., Institute of Electrical and Electronics Engineers. http://ieeexplore.ieee.org/servlet/opac?punumber=7671. STOREY, N. (2004). Electrical & electronic systems. Harlow, Pearson/Prentice Hall. http://www.myilibrary.com?id=106491. Read More