ET 1410 – Integrated Circuits
Project Report

555 Timer as a
Voltage Controlled
Oscillator (VCO)

Student: Earl Ebbert
Student ID: 18970599

ITEM | PAGE | Title Page | 1 | Contents | 2 | Introduction | 2 | Circuit Schematic Diagram: (Fig. 1) | 3 | 555 Timer as a Voltage Controlled Oscillator (VCO) Parts List: (Fig.2) | 3 | LM555CM Datasheet Information: (Fig 3.) | 4 & 5 | 741 Op amp Information: (Fig 4.) | 6 | Formula List: (Fig 5) | 7 | Data Table: Measurements and Calculations (Fig 6) | 7 | Frequency Counter Simulation Readings: (Fig. 7) | 8 | Oscilloscope - XSC1 Measurement Diagrams: (Fig. 9): | 8 | Conclusion and Recommendations: | 9 | References and Citations: | 9 |

Introduction: Oscillators are circuits that generate a periodic waveform to perform timing, control, or communication functions. Oscillators require a form of positive feedback, where a portion of the output signal is fed back to the input in a way that causes it to reinforce itself and thus sustain a continuous output signal. This voltage-controlled oscillator (VCO) Circuit uses the 555 timer as the main component and is configured as an astable multivibrator, switch is able to serve as a free-running nonsinusoidal oscillator that produces a pulse waveform on its output. An astable multivibrator is just a timing circuit whose output oscillates between 'low' and 'high' continuously, in effect generating a train of pulses. The 555 timer is a versatile integrated circuit with many applications (Floyd & Buchla, 2013).

Circuit Schematic Diagram: (Fig. 1)

555 Timer as a Voltage Controlled Oscillator (VCO) Parts List: (Fig.2) Reference # | Part/Item | Listed Value | R1 | Resistor | 100KΩ | R2 | Resistor | 100KΩ | R3 | Resistor | 100KΩ | R4 | Resistor | 100KΩ | R5 | Resistor | 100KΩ | C1 | Capacitor | 0.01 μF | U1 | Timer/Oscillator Circuit | LM555CM | U2 | Op-Amp | 741 | V1 | DC Power Supply | - 12 Volts | V2 | DC Power Supply | 2 Volts to 12 Volts | VCC | Positive Digital Supply Voltage | 12 Volts | VDD | Positive Digital Supply Voltage | 12 Volts | VEE | Negative Digital Supply Voltage | - 12 Volts |
LM555CM Datasheet Information: (Fig 3.) Visual Image | Features | | | Internal Schematic Diagram | |
(Instruments, 2015)

LM555CM Datasheet Information (Continued): (Fig 3.) LM555CM Specifications |

741 Op amp Datasheet Information: (Fig 4.) | | 741 Op-Amp Specifications | .Supply Voltage | +/- 18 | Volts | Output impedance | 75 | Ohms | Supply Current (Max) | 28 | mA | Output Load | >= 2000 | Ohms | Power Consumption (Max) | 100 | mW | Output 2,000 ohms (Min) | +/- 10 | Volts | Input Voltage | +/- 15 | Volts | Output 10,000 ohms (Min) | +/- 12 | Volts | Input Bias (Typical) | 80 | nA | Minimum Gain | 20,000 | | Input Bias (Max) | 500 | nA | Maximum Gain | 200,000 | | Input Resistance | 1 - 3 | 1M Ohms | Slew Rate | 0.5 | 0.5 v/�s | Output | 20 | mA | Frequency x Gain | 1,000,000 | | Internal Schematic Diagram |
(TI, 2013)

Formula List: (Fig 5) Formulas for 555 Timer as a Voltage Controlled Oscillator (VCO) | Duty Cycle Calculations V2 = Applied Voltage 2 Volts: (2.51 ms ÷ 3.21 msec) * 100 = 78.20 Where T = Period 4 Volts: (1.39 ms ÷ 2.09 msec) * 100 = 66.51 PW = Pulse Positive 6 Volts: (813.94 us ÷ 1.51 msec) * 100 = 53.90 F = Frequency 8 Volts: (448.08 us ÷ 1.15 msec) * 100 = 38.96 Duty Cycle = (PW ÷ T) * 10010 Volts: (192.41 us ÷ 894.61 usec) * 100 = 21.51 Voltmeter = Reading12 Volts: = 0.001` |

Data Table: Measurements and Calculations (Fig 6)

V2 | T | PW | F | Duty Cycle | Voltmeter | 2 Volts | 3.21 msec | 2.51 ms | 311.55 Hz | 78.20 | 10.01 V | 4 Volts | 2.09 msec | 1.39 ms | 479.52 Hz | 66.51 | 8.01 V | 6 Volts | 1.51 msec | 813.94 us | 662.50 Hz | 53.90 | 6.01 V | 8 Volts | 1.15 msec | 448.08 us | 873.23 Hz | 38.96 | 4.01 V | 10 Volts | 894.61 usec | 192.41 us | 1.12 kHz | 21.51 | 2.01 V | 12 Volts | --- | --- | --- | --- | .01 V |

Frequency Counter Simulation Readings: (Fig. 7)

Oscilloscope - XSC1 Measurement Diagram: (Fig. 9):

Conclusion and Recommendations: The objective of the 555 Timer as a Voltage Controlled
Oscillator (VCO) circuit project was to validate the pre-lab calculated measurements and design values by building the actual circuit in NI Multisim. The voltage panel meter measured the output (control voltage) of the summing amplifier (Formula –V1+V2), voltage was increased in V2 by increments of 2 volts to adjust the frequency output of the Frequency Counter. The frequency readings were used as an indicator of any distortion to the waveform through the
Oscilloscope. The data analysis relieved that if the output frequency increased then the duty cycle and the pulse width decreased until the Formula –V1+V2= zero. The duty cycle is the ratio of the time the output is “ON” to the total time of the cycle (T).

References and Citations:

Diffley, J. (2015, July 1). Oscillator Circuits. Retrieved from All About Circuits: http://www.allaboutcircuits.com/worksheets/oscillator-circuits/ Floyd, T. L., & Buchla, D. M. (2013). Analog fundamentals : a systems approach. Upper Saddle River, New Jersey 07458: Pearson Education, Inc.

Texas Instruments (2015). LM555 Timer. Retrieved from Texas Instruments.com: http://www.ti.com/lit/ds/symlink/lm555.pdf Texas Instruments (2013). Texas Instruments.com. Retrieved from LM741 Operational Amp: http://www.ti.com/lit/ds/symlink/lm741.pdf NI Multisim (2013). National Instruments Multisim software program. http://www.ni.com/