Design and Testing of a Delay Unit: Voltage Controlled Oscillator - Lab Report Example

Design and Testing of a Delay Unit Design and Testing of a Delay Unit PART 4: EXPERIMENT: DESIGN AND TESTING OF A DELAY UNIT AIMS and OBJECTIVES: Exploring the property of 555 chip with the help of different experiments Designing and testing a Voltage Controlled Oscillator (VCO) Building a 555 chip-based delay unit Designing and building a trigger circuit Enhancing practical skills THEORY OF THE EXPERIMENT: Voltage Controlled Oscillator (VCO) is a module, which is responsible for generating the audible frequency notes for human ears.  The user can test the pitch sources, while setting the required tune through this module. Accordingly, a VCO is similar to a string of a guitar, as the plucking of the guitar string also generates the desired note. The VCO comprises of an input voltage (IV)/OCT with constant voltage (CV) input, which comes from the controller of keyboard. This CV is responsible to change the VCO pitch, just like the changes brought by the guitar string in a guitar. As varying input voltage changes output frequency of the VCO, it is also known as “voltage-to-frequency converter”. As shown in the following figure, Pin 5 terminal of a VCO is the voltage control pin. This pin regulates the trigger to threshold the applied signal levels. Usually, the applied VCC voltage at the supply pin is more as control voltage will be two-third of the supply pin voltage. The in-built voltage divider causes this division. The pin can also have direct voltage from an external source through a voltage regulating potentiometer. The time for capacitor charging and discharging shall increase with corresponding voltage increase, while the reverse is true in case of decreasing the applied voltage. Hence, the frequency variation is directly reciprocal to the applied voltage, also known as control voltage. A potentiometer or a transistor circuit output can supply such input control voltage. Figure 1.0, given below, displays the example of a VCO circuit (A.M Bhatt 2012 n.d) (Figure 1.0: a VCO circuit, Source:…) A chip called “555 timer IC’ is the core component of a voltage-controlled oscillator. Accordingly, its use as an oscillator requires its configuration, before using it, for forming a stable multi-vibrator. A stable multi-vibrator is a timing circuit that has an output of constant oscillation, between the given logic of high and low, without any stopping in between. This produces a complete chain of pulses. While the circuit with only standard “555 timer” cannot be connected to any external voltage supply, the “555tmer IC” circuit has the capability of being connected to such voltage supply source through pin 5. The user can regulate the threshold voltage though this pin, which is the control voltage pin. The threshold voltage at pin 5 is compared to voltages prevailing at pin 2 and pin 6 through the in-built voltage comparators. The in-built flip-flop circuits are usually controlled by the outputs received from these comparators, as these circuits toggle the output of 555 timer. Adjustment of control voltage applied to pin five results in the 555 timer output frequency variation. Accordingly, an increased voltage application at pin 5 will result in reduced output oscillation frequency, while decreasing pin five voltage will increase this frequency.         EQUIPMENTS AND COMPONENTS USED: Equipment: Breadboard, DC Power Supply Unit (PSU), Digital Multi-Meter (DMM), Oscilloscope Components: Resistors (Ω): 330kΩ, 200k, 5×100k, 2×5.1k, 1k, 82, Capacitors (F): 10n, 22n 100μ (Tantalum), Chips: LMC555CN), LEDs: LED, Switch: On/Off Switch Figure 1.1: a 555 timer based VRO (Source: ….) The above figure shows the circuit for Voltage Control Oscillator that uses 555 timer IC PROCEDURE FOR THE EXPERIMENT A breadboard was used to design and build the 555-based oscillator, as shown figure 1.3 Figure 1.3: A VRO circuit Voltages at V2 and Vout were recorded with durations of their timing at maximum and minimum values. Observations were recorded after increasing the RA to 330 kΩ . Test 1 was repeated after resetting the RA to 100 kΩ and RB to 330 kΩ . Test 1 was again repeated after setting the values of RA and RB to remain equal to 100kΩ, while reducing the supply voltage to 6 volts. Test 1 was repeated after setting the supply voltage to 3 V. Pin 5 was given a current of 5V, while setting Vcc to 9V. Thereafter voltage V5 was regulated between 0 to 8 volts, in steps of one to four. The frequency along with minimum, maximum values of V2 and Vout were recorded. The following is the chart that shows the maximum values of V2 and Vout, as well as minimum value of V2. Accordingly, a graph was plotted with these values, along with the frequency recorded at V5. RESULTS AND DISCUSSION QUESTIONS FOR DISCUSSION The observations recorded after comparison of Vout waveform with the Vc waveform with 555 timer oscillator and NOR gate based oscillator revealed that the 555 timer oscillator gives a square wave, while NOR gate based oscillator produces a triangular wave. It was observed that with increase in RA and resistance values, the wave amplitudes also increased proportionally. The output voltage value also increased proportionally going up from 2.8 V to 10 V. The observations revealed that duration for Vout, set at high, decreased from 2.98ms to 1.386ms after setting RA to 100 kΩ and RB to 330kΩ. However, it was observed that duration of Vout set to low remained constant in similar settings. The following voltage results were recorded after setting RA and RB to same value of 100kΩ while reducing the supply voltage to 6V. Maximum voltage= 7 V, minimum voltage= -200mV The values of voltage at different points, as recorded from tests 3 and 4, reveal the following relationship. The maximum value of V2 – Vcc is inversely proportional to V2 The minimum value of V2 - Vcc is directly proportional to V2 The maximum value of Vout - Vcc is directly proportional to Vout. GRAPHS Why frequency changes? While frequency is inversely proportional to capacitance, any change in impedance for the circuit will result in capacitance variation. Voltage change causes the corresponding change in the impedance. Hence, the frequency change occurs, which is regulated by the equation, frequency = 1/ (1.386R2*C) PART 5: CONFIGURATION AND CALIBRATION OBJECTIVES: Interfacing the oscillators and amplifier and the delay unit Calibrating the system Enhancing practical skills Theory for experiment Oscillators Any oscillator circuit that generates oscillating periodic signal, electronic signal as well as occasional square or sine waveform is known as an oscillator. While electronic devices can work as oscillators, these are capable of converting direct current (DC) to alternate current (AC) signals. The examples of such signals include clock signals from computers, TV and radio broadcast signals and circuit of crystal quartz clocks. In addition, the electronic beeper sounds as well as videogame sounds are examples of these signals. EQUIPMENT AND COMPONENTS Equipment: Breadboard, DC Power Supply Unit (PSU), Battery: 9V with connectors, Digital Multi-Meter (DMM), Oscilloscope, Screwdriver Components: Resistors (O): 10k, 300k, 5×620k, Capacitors (F): 33µ, Potentiometer (O): 50k Linear Carbon, Multi-position switch Note: All resistors have Metal Film (: 1%) with wattage rating as 0.25 EXPERIMENTAL PROCEDURE 1. Interfacing Connecting the delay unit to the oscillator as shown in the following figure 2. Calibration a. Connecting the potentiometer as shown in the figure b. Adjusting delay to 60 sec for values of R3=620kΩ, 3. Using a multi-position switch, building the circuit as given in fig. 5.3 multi-position, the delay unit was tested and results recorded for each value of R3. 4. The following observations were recorded as the power supply was provided through a 9V battery. RESULTS AND DISCUSSION Delay(min) 0.5 1 2 3 4 5 R3(k) 310 620 1240 1860 2480 3100 Discussion questions Q1: What is the requirement of ‘control signal’, as high or low, for disabling the NOR gate? (Hint: Logical properties of NOR gates may be used) Answer: the control signal must be high to disable the NOR gate. Q2: Prior to reaching the required delay, what shall be the output of delay unit (pin 3 of 555) ? Answer: Vout shall be 9 V 4. Q1: What is the function of C5? 5. Answer: The function of this capacitor is to ensure that there is no loss of power in the system, as it goes through charging and discharging cycle. 6. Q2: What is the reason to use two switches (S1 and S2)? 7. Answer: While S1 switches the system ‘on’ and ‘off’, according to the capacitor status, S2 functions as a safety switch to protect components in case of any faulty function. CONCLUSION Various procedures were employed in the experiment for developing the voltage controlled oscillator. Accordingly, during the VCO design, observations were recorded for the change in properties of different parameters in relation to each other. This increased our knowledge about 555 timer-based oscillators. In addition, we could observe the comparison in waveforms, as 555 timer based oscillator has a rectangular shaped wave, while the NOR gate-based oscillator has a triangular wave. References 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