Designing and Testing of a Delay Unit - Lab Report Example

Designing and Testing of a Delay Unit PART 4: EXPERIMENT: DESIGNING AND TESTING OF A DELAY UNIT THE OBJECTIVES ARE To investigate the property of 555 chip through tests 2) To construct a 555-based delay unit 3) To design and test a Voltage Controlled Oscillator (VCO) 4) To design and build a trigger circuit 5) To strengthen my practical skills THEORY OF THE EXPERIMENT: Voltage Controlled Oscillator (VCO) is a module that generates the frequency of the notes capable of being heard by human ears.  This permits the user to correctly "tune and set" the pitch source.  A VCO can be equated to a single string from a guitar.  A pluck generates a specific note. A VCO has a 1V/OCT CV input.  The CV originates principally from the keyboard controller.  This CV modifies the pitch of the VCO the same way a guitar string changes the guitar. The VCO circuit can also be called a voltage-to-frequency converter as its output frequency can be varied by varying the input voltage. VCO Pin 5 terminal the voltage control pin has the function of regulating the trigger and the threshold levels of the applied signal. Mostly the control voltage is 2/3 of the VCC voltage applied at the supply pin as a result of the inside built voltage divider. This pin can also be supplied with an external voltage straight through a potentiometer. This external voltage can be varied by adjusting the potentiometer. Decreasing or increasing the applied voltage elongates or shortens the capacitors charging and discharging time. Consequently, it can be inferred that the frequency can be varied by effectively varying the applied input voltage (control voltage). This control voltage can be supplied to the pin via the potentiometer. Parenthetically, it may be supplied via a transistor circuit’s output. Figure 1.0 shows a sample of a VCO circuit (A.M Bhatt 2012 n.d) Further it is important to note that Voltage-controlled oscillator uses the 555 timer IC as the core constituent. IC should be constructed first to form a stable multi-vibrator before it is used as an oscillator. A stable multi-vibrator can be described as a timing circuit with an output that oscillates between the logics low and high continuously, as a result, it creates a full train of pulses. The chief difference between this circuit and the standard 555 timer circuit is that the 555s pin 5 is linked to an external voltage supply.  Pin 5 is the 555s control voltage pin. This pin lets the user to regulate the threshold voltage. This is the voltage that pin 2 and pin 6 are compared to by the internally built comparators. The outputs from these comparators usually controls the internally constructed flip flop circuits that toggles 555 timer’s output, then, regulating the control voltage at pin 5 varies the frequency at which the 555 timer’s output is changed at. Increased voltage at pin 5 decreases the output alternation frequency. Decreasing this voltage increase the alternation frequency at the output.         EQUIPMENTS AND COMPONENTS USED: Equipment: 1. DC Power Supply Unit (PSU), 2. Oscilloscope 3. Digital Multi-Meter (DMM), 4. Breadboard, Components: 1. Resistors (Ω): 330kΩ, 200k, 5×100k, 2×5.1k, 1k, 82, 2. Capacitors (F): 10n, 22n 100μ (Tantalum), 3. Chips: LMC555CN), 4. LEDs: LED, 5. Switch: On/Off Switch Figure 1.1: a 555 timer based VRO EXPERIMENTAL PROCEDURE 555-based oscillator was designed and built on a breadboard as shown figure 1.3 Figure 1.3: A VRO circuit TASKS 1) RA was increased to 330 kΩ and observations recorded. 2) Maximum and minimum values of V2 and Vout, and the durations were recorded. 3) RA was reset to 100 kΩ and RB changed to 330kΩ and test 1 was repeated 4) The supply voltage was reduced to 3V and the test 1 was repeated 5) The minimum and maximum values of V2 and Vout together with the frequency were recorded. 6) Vcc was set to 9V and a voltage of 5V was applied to pin 5. Then V5 was changed between 0 and 8 V in steps of 1V. 7) RA was set to be equal to RB =100kΩ and the supply voltage was reduced to 6V and test 1 repeated. 8) A graph of V2 (Maximum), V2 (Minimum), Vout (Maximum), and frequency against V5 was strategized. RESULTS AND DISCUSSION. QUESTIONS RELEVANT FOR DISCUSSION. a) Associating the waveform of Vout with the waveform of VC for the NOR gate based oscillator can it be concluded that the waveform for the 555 timer oscillator is square wave while for the NOR gate based oscillator was a triangular wave? b) Can it be observed that when the value of RA was augmented or increased, the amplitudes of the waves increase proportionately with the increase in the value of resistance? c) Can it also be inferred that the output voltage value increases proportionally from 2.8 V to 10 V? and d) Setting RA to 100 kΩ and RB to 330kΩ. Then the duration for Vout =’high’ decreases from 2.98ms to 1.386ms while the Vout =’low’ duration remains constant, and e) When RA was set to be equal to RB=100kΩ and the supply voltage was reduced to 6V, then the Maximum voltage = 7 V, minimum voltage = -200mV. Based on the tests 3 and 4, then the relationship between the following values is as follows: 1. The minimum value of V2 - Vcc is directly proportional to V2 2. The maximum value of V2 – Vcc is inversely proportional to V 3. The maximum value of Vout - Vcc is directly proportional to Vout. GRAPHS Why frequency changes? Because the voltage change also changes the impedance for the circuit denoting that the capacitance is changed. Frequency is inversely proportional to the capacitance. And is correlated by the equation= 1/ (1.386R2*C) PART 5: PUTTING TOGETHER AND CALIBRATION OBJECTIVES: 1. To interface the delay unit, oscillators and amplifier 2. To calibrate the system 3. To strengthen practical skills 4. Theory of experiment Oscillators An oscillator is an oscillator circuit that generates oscillating electronic signal, periodic signal or at times square waveforms or sine waveforms. From the source they change direct current to AC signals (Alternating Current). Some obvious examples of signals produced by oscillators include but not limited to broadcasted signals, computer’s clock signals and crystal quartz clock circuits. Sounds produced from video games and by electronic beepers are also examples these signals. COMPONENTS AND EQUIPMENT Equipment: Breadboard, 1. Battery: 9V with connectors, 1. Oscilloscope, 2. Screwdriver 1. DC Power Supply Unit (PSU), 3. Digital Multi-Meter (DMM), Components: Resistors (O): 10k, 300k, 5×620k, 1. Potentiometer (O): 50k 2. Linear Carbon, 3. Multi-position switch 4. Capacitors (F): 33µ, NOTE: All resistors are of 0.25W Metal Film: (1%) EXPERIMENTAL PROCEDURES 1. Interfacing. The delay unit was linked to the oscillator as presented in the figure 2. Calibration a. The potentiometer was linked as shown in the figure b. For R3=620kΩ, the delay was adjusted to 60 sec 3. The circuit given in fig. 5.3 was built using a multi-position switch, and analysis for the delay was done and documented for each value of R3. 4. The power source was replaced with a 9V battery, observations made. RESULTS AND DISCUSSION Delay(min) 0.5 1 2 3 4 5 R3(k) 310 620 1240 1860 2480 3100 DISCUSSION QUESTIONS 1. To inactivate the above NOR gate, should the ‘control signal’ be ‘high’ or ‘low’? (Clue/Hint: Use the logical possessions of NOR gates) Answer: the control signal should be high for disabling. 2. What is the output of the delay unit (pin 3 of 555) before the necessary delay is arrived at? Answer: Vout =9 V 3. What is the function of C5? Answer: this capacitor is used ensure that the system does not lose power since it will be charging and discharging at intervals. 4. Why do we use two switches (S1 and S2)? Answer: S2 is a safety switch because it safeguards the components in case of any failure. S1 is the systems switch for switching on and off based on status of the capacitor. CONCLUSION The voltage controlled oscillator was built and tested by doing a number of procedures in the experiment. The properties of change in different parameters relative to others were detected in designing the VCO, this has reinforced our practical skills on 555 timer based oscillators. Similarly comparison revealed that the wave-form for 555 timer based oscillator is rectangular while that of a NOR gate-based oscillator is a triangular wave. References List Professor Barry Parton 1998, Fundamentals of Digital Electronics, National Instrument Corporation John Bird 2007, Electrical and Electronics Principals and Technology, third edition Newnes Elsivier UK Collin Mitchell 2012, 50-555 timer circuits, Talking Electronics Anil K. Maini 2007, Digital Electronics, Principle, Devices and Application, John Wiley and Son Limited, England Read More