Donald E. Jones

Schematics of Special Devices Used in This Book

With one exception, circuit layout and parts placement are not critical for any of the circuits involved. The exception is that, when they are required in the circuit, the 0.01-μF ceramic power-supply decoupling capacitors must be placed between the power-supply connections and ground as close to each logic device and operational amplifier as possible. This will prevent noise transients and oscillations from occurring as a result of power-supply-wiring inductances. In addition, reasonable care should be taken to prevent internal ground loops in the devices. Power-supply requirements are fairly noncritical. The supplies should, however, be regulated and have current capacities on the order of about 100 mA for the + 15-V unit, and about 200 mA for the + 5-V unit. Inexpensive epoxy-encapsulated units such as Computer Products (Fort Lauderdale, Fla.) Models PM529 (for +5-V unit) and PM552 (for ± 15-V unit) can be used.

Purdue REAL-TIME BASIC

The high-level programming language for on-line experimentation developed at Purdue University was built around the basic language and will be referred to as Purdue REAL-TIME BASIC (PRTB). The software was developed by modifying the BASIC Interpreter available from Hewlett-Packard (H.P. 20392). The modifications generated have involved the development of a series of machine-language subroutines which are directly callable from the BASIC software and which are designed to communicate in a variety of ways with experimental systems. The characteristics of the PRTB data-acquisition and control software are exactly analogous to those described in Sec. II.

On-Line Digital Computer Applications for Kinetic Analysis

The experiment described here is one in which both kinetic methods of analysis and a computer employed in an on-line configuration are used to solve an analytical problem (see ref. E-6). In this experiment you will determine the concentration of glucose in the 10–100 ppm range by measuring its oxidation rate in the presence of the enzyme glucose oxidase.

Graphic-Display Experiments Using an X-Y Plotter and/or Storage Oscilloscope

The computer provides a speedy method for the evaluation and display of functions. This is highly desirable in curve fitting, data smoothing, or plotting of real or simulated data. In order that he may use these capabilities, it is necessary that the user understand the particular problems associated with plotting functions. It is the objective of this experiment to provide an opportunity for the student to develop an appreciation of the use of graphic-display techniques through programming exercises involving both simple function

REAL-TIME BASIC (RTB) for Varian 620 Computers (Oregon/Nebraska Version)

The basic programming approach described in this section may be implemented on Varian 620/i, 620/L, and 620/f computers. In addition, the Varian 73 computer can be used in the same way. Our development of real-time basic (rtb) for these systems has relied on simple modifications of the basic compiler as supplied by Varian. This compiler is a version of the language, originally developed at Dartmouth College, which includes all of the standard arithmetic operations as well as trigonometric functions and matrix-algebra routines. The standard Varian version of the language requires approximately seven thousand words of memory for the compiler, leaving the remainder available for user source code. A user may expand the available source-code area (thus allowing larger programs) by deletion of the matrix algebra and/or trigonometric function packages. This yields about 700 additional words of memory. Since this is a true interpretive compiler, all user source code and the compiler must be stored in core at run time. It is possible to modify the compiler to use a mass storage device (i.e., magnetic disk) to store user source code. At least one user has done this; however, such a procedure slows execution times and is not generally suitable for real-time experimentation. As released by Varian, basic contains no subroutines to support devices of the type needed in the laboratory (i.e., analog and digital I/O devices, control and sense lines, etc.).

Equipment and Reagents List

TTL series 7400 dual-in-line packages are usually specified. Instructors may optionally substitute alternate equivalent components.

Detailed Description of Data-Acquisition Interface for Hewlett-Packard 2100-Family Computer Systems

Some minicomputer manufacturers also offer general-purpose laboratory data-acquisition-interface hardware as an optional accessory. Typical examples are the LAB-8 and LAB-11 systems offered by the Digital Equipment Corporation. However, if that option is not available, or if the available hardware is not completely suitable for the educational environment, it may be necessary to construct the interface for your particular minicomputer system. This was the case for the laboratory computer system used at Purdue. In this Appendix we will describe the design philosophy and detailed characteristics of the laboratory interface developed for the Hewlett-Packard 2100-family (models 2116, 2115, 2114, 2100, and 21 MX) of minicomputers.

Properties and Use of Digital-to-Analog (DAC) and Analog-to-Digital (ADC) Converters

Most laboratory instruments either produce or accept analog or continuous signals of some form. In order for a digital computer to be able to communicate with an analog instrument, digital-analog interconversions must be made. There are several different ways to construct devices to accomplish this. A digital-to-analog converter (DAC) can be constructed using a weighted resistor or ladder resistor network. The ladder resistor network is the more frequently used because it requires only two different values of precision resistors and is therefore cheaper to construct. However, the weighted resistor network is easier to conceptualize, and will be discussed first. Figure 5–1 shows the diagram of a typical four-bit DAC, constructed from a weighted resistor network. At any particular time, the value of the current at the inverting input of the operational amplifier is inversely proportional to the values of the resistors in the circuit and directly proportional to V R . The (inverted) output voltage, V out , depends on these parameters and on the value of R f . The exact relationship is shown in Eq. (5–1), where Lt denotes the logical state of the switch adjacent to the ith resistor. The quantity L is 1 for closed switches and 0 for open switches.

Multiplexing Using Triggerable Distinct Waveforms

It is very often desirable to use a single transmission channel or wire for the sequential transmission of signals derived from several sources. This method can be thought of as a simple “time-sharing” approach to the use of the channel, in that each signal source is allotted a certain portion of the available time for its use of the channel. Obviously, if each of N signal sources is allocated an equal portion of the total time available, then 1/N is the fraction available for any single source. This procedure is called “multiplexing” and may be used equally well with either digital or analog signals. These two types of multiplexing are represented schematically in Fig. 11–1.

Interpreting Specifications Found on Digital Integrated-Circuit Data Sheets

In order to perform the experiments in this manual, it will be necessary to read and interpret the data sheets of various integrated circuits. This appendix provides sufficient information for students to wire and use most common integrated-circuit packages and all the packages used in this book. The appendix also discusses several specifications which are important from a design standpoint but need not be understood before performing the experiments. (Indeed, several of the experiments were designed to teach these concepts. For instance, a timing diagram will be more meaningful after the student has completed Experiments 2 and 3.) Thus, this appendix should be reread after completing Experiments 1 through 5.