Project 3 build an astable multivibrator
Download
1 / 22

Project 3 Build an Astable Multivibrator - PowerPoint PPT Presentation


  • 147 Views
  • Updated On :

Project 3 Build an Astable Multivibrator. Purpose. The purpose of this project is to build an Astable multivibrator without the 555-timer chip. This means you will have to assemble your own components to mimic the behavior of the inside of the chip.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Project 3 Build an Astable Multivibrator' - linus


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Project 3 build an astable multivibrator l.jpg

Project 3Build an Astable Multivibrator


Purpose l.jpg
Purpose

  • The purpose of this project is to build an Astable multivibrator without the 555-timer chip.

  • This means you will have to assemble your own components to mimic the behavior of the inside of the chip.

  • You will create a PSpice simulation and a working circuit.

  • You will then modify the 555 timer chip model so that it cycles over a different part of the capacitor charge curve.

  • You will modify your PSpice simulation and circuit to demonstrate that your new model works as predicted.

Electronic Instrumentation


Slide3 l.jpg

The Animation

Animation applet

Your initial design will be a PSpice simulation and working circuit based on this animation.

Electronic Instrumentation


Block diagram l.jpg
Block Diagram

  • Circuits are often represented by block diagrams that show the flow of the signal between different functional blocks.

  • Above is a block diagram of the astable multivibrator.

  • Your circuit won’t include the Reset feature

Electronic Instrumentation


Slide5 l.jpg

Components in each Block

A

G

E

C

D

F

Electronic Instrumentation

B


Components in each block l.jpg
Components in each Block

A: R-R-C Combination

B: Voltage Divider

C: Threshold Comparator

D: Trigger Comparator

E: Reset Logic Chip (NAND gate)

F: SR Flip Flop

G: Transistor Circuit

Electronic Instrumentation


Slide7 l.jpg

How does the Astable Multivibrator work?

What makes this circuit generate a string of pulses?

This is discussed in detail in the experiment 7 notes.

http://www.academy.rpi.edu/5.downloads/modules.html

Electronic Instrumentation


Slide8 l.jpg

How does the Astable Multivibrator work?

2 NOR gates can be used to create a SR Flip-Flop

Convince yourself that this works

Electronic Instrumentation


Slide9 l.jpg

Build this circuit

This has all the 555 Timer features except for the reset pin.

You will build it on the protoboard

Electronic Instrumentation


Slide10 l.jpg

But model this circuit

The demo version of Capture won’t model the circuit you will build. It can model this one, which uses 2 transistors to model the SR Flip-flop.

Electronic Instrumentation


How does the astable multivibrator work l.jpg
How does the Astable Multivibrator work?

These equations determine the characteristics of your output pulses based on the values you choose for R1, R2 and C1.

Electronic Instrumentation


How does the astable multivibrator work12 l.jpg
How does the Astable Multivibrator work?

  • The frequency of the pulses and their duty cycle are dependent upon the RC network values.

  • The capacitor C charges through the series resistors R1 and R2 with a time constant of

    tON = (R1 + R2)C1.

  • The capacitor discharges

    through R2 with a time

    constant of tOFF = R2C1

Electronic Instrumentation


Where do the equations come from l.jpg
Where do the equations come from?

The equations that determine the on and off time of the output pulses are based on the charge and discharge time of the capacitor. The capacitor equations are:

charging

discharging

Electronic Instrumentation


Relating charge equations to time l.jpg
Relating charge equations to time

How much time should it take to charge between 1/3 and 2/3 of V0?

Time to charge up to 2/3V0 is:

Electronic Instrumentation


Initial design pspice l.jpg
Initial Design PSpice

  • Build the PSpice circuit and look at the signals at the input and output of each block in the diagram.

    • No reset circuit

  • Use the cursors to record voltage levels and times

    • high and low on digital signals

    • important points on analog signals (like 1/3 and 2/3 of Vcc)

    • on and off time of the pulses

Electronic Instrumentation


Initial design protoboard l.jpg
Initial Design Protoboard

  • Build the circuit on your protoboard

    • don’t forget to put power on the digital chip

    • add a bypass capacitor

  • Record data using Mobile Studio and the IOBoard

    • Use voltage and time features of scope

    • Use the cursors on the scope

    • Make sure you have labeled the plots with the numerical values recorded

Electronic Instrumentation


Final design l.jpg
Final Design

  • Modify the inside of the timer to make it switch at different voltages.

  • What are the new equations for TON and TOFF?

  • What are the new on and off times for the pulses in your circuit?

  • Modify the PSpice and the circuit on your protoboard and show that your results are consistent with those predicted by the equations.

Electronic Instrumentation


Project report l.jpg
Project Report

  • Introduction

    • What is the objective of the project?

    • At least two relevant topics

  • Theory

    • Describe the function of the components in the circuit

    • How does the multivibrator work? Give details.

    • Where do the equations for TON and TOFF come from?

    • What should TON and TOFF be for the circuit you are building?

Electronic Instrumentation


Project report19 l.jpg
Project Report

  • Initial Design

    • PSpice simulation, plots, and discussion

    • Protoboard implementation, plots, and discussion

    • comparison of voltages and times

      • PSpice

      • Protoboard

      • Theory

Electronic Instrumentation


Project report20 l.jpg
Project Report

  • Final Design

    • Determine new threshold and trigger voltages

    • Come up with the new timing equations

    • Modify PSpice

    • Modify Circuit

    • Comparison of voltages and times

      • voltage levels affected by redesign

      • new on and off times

Electronic Instrumentation


Project report21 l.jpg
Project Report

  • Conclusion

    • Is it an astable multivibrator?

    • Conclusions that can be drawn from your voltage comparisons

    • Discuss the on and off times of the initial and final design. Are they as expected?

    • Sources of error

    • General Conclusions

Electronic Instrumentation


Appendices l.jpg
Appendices

  • Appendix A: Make you own task list.

  • Appendix B: References and initial design equations.

  • Appendix C: PSpice plots of initial design

  • Appendix D: Plots of data from Mobile Studio for initial design

  • Appendix E: Final design (circuit diagram, calculations, PSpice and Mobile Studio plots)

Electronic Instrumentation


ad