Voltage Controlled Oscillator Experiment - Research Paper Example

Voltage Controlled Oscillator Experiment of the al Affiliation PART 4 EXPERIMENT ON DELAY UNIT: Design and Testing The goals of this experiment are:- To investigate the characteristic of the 555 chip To develop a 555- based delay unit Create and subsequent testing of a VC O (Voltage Controlled Oscillator) Invent a trigger circuit Improve on the practical skills related to the course Background Information A circuit –controlled oscillator describes an oscillator whose frequency is fully controlled by a control voltage. The control voltage causes the frequency to rise gradually until its peak and after that fall back to its starting frequency. 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 hence generating frequency that are audible by human ears. It can be likened to a string of guitar whereby if it is plucked, it emanates a particular sound. Normally, all VCOs have 1V/OCT CV input. The CV alters the pitch to desired level just like a string of a guitar does when plucked with measured intensity. This is done mainly from a keyboard controller. A VCO is also termed as voltage-to-frequency converter owing to the fact its output frequency is altered to desired levels by changing the input voltage. The system comprises of a Pin 5 terminal on the voltage control that mainly 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 explained by the presence voltage divider that is installed internally. In case 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 adjusting the potentiometer, the external voltage is adjusted to desired levels. The principle behind is that when the voltage is regulated, the charging and discharging time of the capacitors changes accordingly. From the discussion, we can infer that frequency can be varied by altering the applied input voltage. To do this, 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 integral parts of the VCO is the 555 timer IC. Normally, the IC is configured first before 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, operational amplifier, vacuum tubes 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. With this pin, the user can control the threshold voltage. Pin two and pin six are compared by 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 at depending on the level which 555 timer’s output is toggled at. Increasing voltage at pin five reduces the output oscillation frequency and the vice-versa is also true.         EQUIPMENTS AND COMPONENTS USED: Equipment: Breadboard, Oscilloscope DC Power Supply Unit (PSU), Digital Multi-Meter (DMM), Components: Resistors (Ω): 330kΩ, 200k, 5×100k, 2×5.1k, 1k, 82, Capacitors (F): 10n, 22n 100μ (Tantalum), LEDs: LED, Chips: LMC555CN), 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. A graph of V2 (Maximum), V2 (Minimum), Vout (Maximum), and frequency against V5 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 infer 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, the amplitudes of the waves changed proportionally in line with the adjusted value of the resistance. The output voltage also increased in a proportionate manner from 2.8 V to 10 V. 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= 7 V, 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 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 interface the delay unit, oscillators and amplifier To calibrate the resultant system To improve on theoretical skills imparted in the coursework To learn the rationale behind the theory of the project Oscillators An oscillator refers to an electronic or mechanical device that functions on the principle of oscillation. Oscillation is a periodic variation between two items based on varying level of energy. All kind of oscillator operates on some basic principle whereby the oscillator uses a delicate amplifier whose output is feedback in the input phase. Hence, the signal restarts and keeps going by itself. Through this process a periodic signal, oscillating or sine waveforms or time square waveforms. The oscillator operates by converting direct current from a Alternating Current (AC) source. A classical example of oscillators include signal broadcasted from televisions and radios. COMPONENTS AND EQUIPMENT Equipment: Digital Multi-Meter (DMM), Battery: 9V with connectors, Breadboard, DC Power Supply Unit (PSU), Screwdriver Oscilloscope, Components: Resistors (O): 10k, 300k, 5×620k, Capacitors (F): 33µ, Linear Carbon, Multi-position switch 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 should 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 varied 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. 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. Besides, the experiment illustrated that the waveform can be different. For instance, NOR gate based oscillator gives a triangular wave while a 555 timer based gives a rectangular wave. References Anil K. Maini 2007, Digital Electronics, Principle, Devices and Application, John Wiley and Son Limited, England         Read More