Experiment of Voltage Controlled Oscillator - Assignment Example

An Experiment of Voltage Controlled Oscillator of School Part 4 Experiment on Delay Unit: Design and Testing The following are the main goals of this experiment: to create a trigger circuit, to develop a 555- based delay unit, to investigate the distinctive characteristic of the 555 chip, to create and to test the Voltage Controlled Oscillator of (VCO), and to improve on the practical skills related to this course. Background Information A circuit –controlled oscillator refers to an oscillator whose frequency is fully controlled by a control voltage. In a circuit-controlled oscillator, the control voltage makes the frequency to gradually rise till it reaches its peak, and after that the frequency fall back to its starting frequency. In a circuit-controlled oscillator, the harnessed input voltage controls the instant oscillation frequency. By using a control input voltage the user can tune and set with precision the pitch source, therefore, generating frequency that one can hear. This can be likened to a string of guitar, whereby, if of one of the strings is plucked, it gives out a particular sound distinctive sound. Ordinarily, all VCOs have 1V/OCT CV input. Just as a string of a guitar does when plucked with measured intensity, the CV alters the pitch to a desired level; this is normally done from a keyboard controller. Due to the fact that the output frequency of A VCO is altered to desired levels by changing the input voltage, the A VCO is also called voltage-to-frequency converter. The system is composed of a Pin 5 terminal on the voltage control that functions to regulate the trigger and threshold levels of the applied signals. Normally, the control voltage equals to two-thirds of the voltage at the supply source. This can be accounted for by the presence of the voltage divider that is internally installed. In circumstances where the user wants a higher or lower regulator, the pin can manage to transmit different levels of voltage by operating it through a potentiometer. By changing and adjusting the potentiometer, the external voltage is adjusted to desired levels. This can be explained by the fact that, when the voltage is regulated, the charging and discharging time of the capacitors also changes. From this explanation, we can, therefore, conclude that frequency can be changed by changing the applied input voltage. To do this, however, the voltage is operated from the potentiometer. Alternatively, it is possible to operate it from the circuit output. Figure 1.0 shows an example of a VCO circuit (A.M Bhatt 2012 n.d) Figure 1.0: a VCO circuit One of the important parts of the VCO is the 555 timer IC. Usually, the IC is configured first before being used as an oscillator to form a stable multi-vibrator. A stable multi-vibrator comprises of two amplifying levels linked to a positive feedback loop by using two capacitive-resistance joining networks. The element that functions as an amplifier can be field-effect transistor, vacuum tubes, operational amplifier, or any other form of amplifier. It has a timing circuit that oscillates from ‘high’ to ‘low’ continuously creating a train of impulses. What distinguishes a stable multi-vibrator and 555 timer IC is that the 555’s pin has an external connection to the voltage supply. Through this pin, the user can control the threshold voltage. Pin two and pin six are normally compared with comparators that are installed internally. The output resulting from these comparators usually control the internal built flip flop circuits that buckles up 555 timer’s output and subsequently changes voltage at pin five with varying frequency, depending with the level which 555 timer’s output is toggled at. Increasing voltage at pin five usually reduces the output oscillation frequency and vice-versa.         Equipment and Components Used The equipment used in this experiment are, Breadboard, Oscilloscope, DC Power Supply Unit (PSU), and the Digital Multi-Meter (DMM). On the other hand, the components of this experiment are Resistors (Ω): 330kΩ, 200k, 5×100k, 2×5.1k, 1k, 82, Capacitors (F): 10n, 22n 100μ (Tantalum), LEDs: LED, Chips: LMC555CN), and 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 Maximum and minimum values of V2 and Vout, and the durations were recorded. RA was increased to 330 kΩ and observations recorded. RA was reset to 100 kΩ and RB changed to 330kΩ and test 1 was repeated RA was set to be equal to RB=100kΩ and the supply voltage was reduced to 6V and test 1 repeated. The supply voltage was reduced to 3V and the test 1 was repeated 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. The minimum and maximum values of V2 and Vout together with the frequency were recorded. Following the results of the experiment, a graph of V2 (Maximum), V2 (Minimum), Vout (Maximum), and frequency against V5 was plotted. Below is the graph that was plotted. Results and Discussion Discussion Questions Comparison of waveform of Vc with waveform of Vout for the NOR gate based oscillator From the data, we can conclude that the waveform for the 555 time oscillator results in a square wave. On the other hand, waveform for NOR gate based oscillator resulted to a triangular wave. During the experiment, it was also observed that when the value of RA was adjusted or changed, the amplitudes of the waves changed proportionally in accordance with the adjusted value of the resistance. The output voltage also increased in proportionally from 2.8 V to 10 V. In setting RA to 100 kΩ and RB to 330kΩ , it was observed that the duration for Vout=’high’ decreases from 2.98ms to 1.386ms while the Vout=’low’ period stay constant. When RA was set to be equal to RB=100kΩ and the supply voltage was reduced to 6V, then the Maximum voltage was= 7 V, and the minimum voltage= -200mV Basing on the tests 3 and 4, we can summarize the relationship between the following values is as follows: The maximum value of V2 – Vcc is inversely proportional to V2 The maximum value of Vout - Vcc is directly proportional to Vout. The minimum value of V2 - Vcc is directly proportional to V2 Graphs The rationale behind changing frequency What causes the frequency to vary is the fact that the change in voltage also leads to modification of impedance for the circuit hence changing the capacitance. Frequency is inversely proportional to the capacitance. And is related by the equation= 1/ (1.386R2*C) Part 5: Putting Together and Calibration The goals of this experiment are: To calibrate the resultant system To interface the delay unit, oscillators and amplifier To learn the rationale behind the theory of the project To improve on theoretical skills imparted in the coursework Oscillators An oscillator is an electronic or mechanical device that functions on the principle of oscillation. Oscillation refers to a periodic variation between two items based on varying level of energy. All kinds of oscillators operate on some basic principle whereby the oscillator uses a delicate amplifier whose output is feedback in the input phase. For this reason, therefore, the signal restarts and keeps going by itself. Through this process a periodic signal, oscillating or sine waveforms or time square wave forms. The oscillator operates by converting direct current from a Alternating Current (AC) source. A good example of oscillators include signal broadcasted from televisions and radios. Components and Equipment The following are the equipment for this experiment Battery: 9V with connectors, Breadboard, Digital Multi-Meter (DMM), Screwdriver DC Power Supply Unit (PSU), Oscilloscope, Components: Resistors (O): 10k, 300k, 5×620k, Multi-position switch Capacitors (F): 33µ, Linear Carbon, Potentiometer (O): 50k Note: All resistors are of 0.25W Metal Film (: 1%) Experimental Procedure 1. Interfacing The delay unit was connected to the oscillator as shown in the figure 2. Calibration a. The potentiometer was connected 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 testing for the delay was done and recorded for each value of R3. 4. The power supply 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 Q1: If the user wants to disable the named NOR gate above, should the ‘control signal’ be ‘high’ or ‘low’? (Hint: Use the principle operations for NOR gates) Answer: the control signal mus be high for disabling Q2: What is the output of the delay unit (pin 3 of 555) before the required delay is reached? Answer: Vout=9 V 4. Q1: What is the function of C5? Answer: the capacitor ensures the system never run low on power since it discharges and charges at different intervals. 5. Q2: Why is the system applying two switches (S1 and S2)? Answer: S2 acts as a safety switch whereby it protects the components from damage resulting from excessive current flow in case they malfunction. On the other hand, S1 acts as a switch to turn on and off depending on the condition of the capacitor. Conclusion In the experiment, VCO was designed and tested through various methods as we have seen. Observations were made on how changing parameters relative to others affects VCO. Arguably, this builds on the skills acquired in class in a practical manner. Also, the experiment illustrated that the waveform can be different. For example, NOR gate based oscillator gives a triangular wave while a 555 timer based gives a rectangular wave. Reference Anil K. Maini 2007, Digital Electronics, Principle, Devices and Application, John Wiley and Son Limited, England         Read More