Laboratory Design Project II

I forgot to bring home the book to use in completing the writeup for the lab. I have used a question mark in the following for numbers that I do not remember. Use the book to find the right number. I hope this does not cause any confusion.

The object of this experiment is to assemble, evaluate, and simulate a free-running multivibrator and a triangular/square-wave generator. You can read the textbook's treatment of the circuits in sections 10.2 and 10.4 of the text.

For all of the circuits, you should have 100 μF decoupling capacitors from each power supply rail to circuit ground. You should be aware that these capacitors are polar electrolytics which can explode if they are put in with the wrong polarity.

Op amps can oscillate when equipment such as an oscilloscope is connected to a circuit. This is caused by the capacitance of the connecting leads. To minimize these problems, clip a 100 Ω resistor in series with the signal lead to the oscilloscope. Use the other end of the resistor to connect to the proto board.

The 741 op amp has a fairly low slew rate and is not an appropriate op amp for this experiment. You should use one of the BiFET op amps such as the TL071, TL081, LF351, etc. These have a slew rate that is a little more than 10 times that of the 741.

Part One

  1. Assemble the circuit in Fig. 10.7 omitting the resistor R and capacitor C.
  2. Power down the circuit and replace the 10 kΩ resistor with a 5.1 kΩ resistor in series with a 10 kΩ potentiometer connected as a variable resistor. The resistance of the combination can be varied from 5.1 kΩ to 15.1 kΩ.
  3. With C = 0.1 μF, calculate the value of the resistor R in Figure 10.7 that gives an oscillation frequency of 1 kHz.
  4. With the original value of C, observe the effect of changing the value of R to 10 times its original value. The frequency should be 100 Hz. With the original value of R, observe the effect of changing the value of C to 0.1 times its original value. The frequency should be 10 kHz.

Part Two

  1. The circuit of Figure 10.19 shows a 2 op-amp triangular/square-wave generator. We have analyzed this circuit in class with the exception that the resistor R3 was short circuit and the 5 diodes were omitted. The addition of these elements allow the square-wave output to be limited to a value 2VD + VZ independently of the value of the power supply voltages, where VD is the forward bias diode drop and VZ is the breakdown voltage of the zener. Two back-to-back zener diodes could be used for this, but the circuit given in the text is a faster switching circuit because the zener diode is never operated in its forward bias region. Thus the switching time is not limited by its diffusion capacitance, which is the capacitance when it is forward biased. There is a design example in the text for this circuit. The author of the text has the values for R1 and R2 reversed.
  2. Like the square-wave generator circuit, the frequency can be changed by changing one R, one C, or both. Observe the change in frequency by changing each one by a factor of l0 as is specified for the square-wave generator of Part I. Record all waveforms.