Ours is the age of technology, rivaling the industrial revolution in its impact on the course of civilization. Whether the great achievements of technology, and our dependence on them, have improved our lot, or lead inexorably to a ‘strange new world’ we shall not debate here. Instead we focus on the physical laws that make technology possible in the first place. Our aim is to understand and explain modern technology, as distinct from describing it.

Even when the principles underlying a technical process or device are well understood, a great deal of engineering effort and a long manufacturing infrastructure are needed to translate them into practice. In turn, the technical skills that are developed lead to new possibilities in basic research and to new applications. For instance, the laser could have been easily built at the turn of the century; yet it was a long road starting with the development of radar and followed by the invention of the maser that led to the proposal for the laser. The use of computers in so many manufacturing areas and research fields is another example of the interplay between technology and basic science.

Because of the complexity of modern devices and of the rapid advances in all scientific fields, the need for specialization is acute. Thus, often, science students are only vaguely aware of the applications of the principles they have learned, whereas engineering students are too involved to appreciate the power of the physical law.

Microelectronics are found today at the heart of almost every device or machine. Be it an automobile, a cash register or just a digital watch it is controlled by electronic circuits built on small semiconductor chips. While the complexity of the functions performed by these devices has increased by several orders of magnitude their size is continuously decreasing. It is this remarkable achievement that has made possible the development of powerful processors and computers and has even raised the possibility of achieving artificial intelligence.

The basic building block of all microcircuits is the transistor, invented in 1948 by John Bardeen, Walter Brattain and William Shockley at Bell Telephone Laboratories. The first chapter is devoted to a discussion of the transistor beginning with a brief review of the structure of semiconductors and of the motion of charge carriers across junctions. We discuss the p–n junction and bipolar as well as field-effect transistors. We then consider modern techniques used in very large scale integration (VLSI) of circuit elements as exemplified by Metal-Oxide-Silicon (MOS) devices.

In the second chapter we take a broader look at how a processor, or computer, is organized and how it can be built out of individual logical circuit elements or gates. We review binary algebra and consider elementary circuits and the representation of data and of instructions; we also discuss the principles of mass data storage on magnetic devices. Finally we examine the architecture of a typical computer and analyze the sequence of operations in executing a particular task.

Advances in electronics during the past decade have led to a variety of computer based instruments. Manufacturers continually add flexibility to traditional research tools as they introduce devices not previously feasible. With measurements made by computers, keyboards replace switches, real-time graphics is common, powerful software is ready to analyze results, and data are easily saved and/or transferred to larger computers. Another important development is adaptability. Minor changes in software and/or hardware can significantly alter a system's capabilities. This book is for people interested in both digital design and adaptable computer based data acquisition.

The Parallel Data Collector (or PDC) has been developed at Ithaca College. It works on Apple II and on IBM PC/XT/AT and compatible computers. With commercially available I/O ports, it also works with Macintosh and IBM PS/2 machines. The PDC can be a frequency meter, voltage recorder, pulse height analyzer, multichannel scaler and many other instruments. The system supports voltage, time and counting measurements with programmable parameters such as voltage conversion rate, time accuracy and counting interval. This book first describes the design principles and integrated circuits which comprise the PDC and then explains the system itself. The central idea is that it's better to master and apply a few concepts than to acquire a broad background with no particular objective in mind.

This book is mostly a text on digital electronics and interfacing. But it also tells “how to” build a powerful, adaptable data acquisition system. Problems at the end of each chapter reinforce the material and many are suitable for laboratory exercises. The later chapters present the PDC's hardware and software as well as construction details and guidelines for testing and troubleshooting.

Section 3.3 explains the design of a pair of 8-bit input/output ports for the Apple II family of computers. Figure 3.19 is the complete circuit. This appendix is a guide to building the ports. Section E.I lists components and presents a layout. Section E.2 suggests an interfacing cable and connectors. Section E.3 gives wiring instructions. And Section E.4 out lines testing and troubleshooting. The objective is a complete presentation of one construction approach. Details such as connectors and cables are somewhat arbitrary and other schemes may be substituted.

Components and Layout

The circuit in Figure 3.19 requires the following components.

1. (1) A Vector Model 4609 wire wrap board for the Apple II expansion slot.

2. (2) Four 74LS373 latch/buffers.

3. (3) One 74LS04 INVERTER.

4. (4) One 74LS138 decoder.

5. (5) Six IC sockets: four 20-pen, one 16-pin and one 14-pin.

6. (6) A bag of Vector T44 wire wrap terminals.

7. (7) Three .01 μf disc capacitors.

8. (8) A wire wrap tool and an assortment of wire.

Vendors for these components are in Appendix B.

Figure E.I suggests a layout for the circuit on the expansion board. The view is from the components side with the rear of the computer on the right. Along the bottom, just above the plug, are pads for wire wrap terminals. When inserted, the terminals allow expansion slot signals to be connected to the ports circuit. The lower row starts with 1 on the left and ends on the right at 25 (which is +5). The upper row starts on the right with 26 (which is ground) and ends on the left at 50.

Modern Integrated Circuits (IC's) have changed the effort and skills required to design and construct systems which carry out sophisticated digital operations. While it's desirable to understand how IC's work in terms of semiconductor physics and while good engineering practices are necessary in commercial products, it's now possible to successfully put together data acquisition hardware without first mastering these subjects.

Only fifteen different IC's are required for the parallel ports circuits of Chapter 3, for the analog-to-digital converter, memory and programmable interval counter circuits of Chapters 4-6, and for the measurement systems of Chapters 7-10. The purpose of this chapter is to introduce these and a few other IC's as well as associated design principles. Section 2.1 covers basic logic gates. Section 2.2 introduces integrated circuits, breadboarding and troubleshooting. Section 2.3 presents digital clocks. Section 2.4 introduces the 7474 flip-flop and a variety of timing and control operations. Section 2.5 outlines electrical properties of logic gates. Section 2.6 presents binary, hexadecimal and decimal number systems. Section 2.7 covers the 74192 and 74193 counters and several applications. Section 2.8 presents the 74138 decoder/demultiplexer and additional control applications. Section 2.9 introduces the 74152 multiplexer. And Section 2.10 presents tri-state gates, buses and the 74373 and 74244 buffers. While these topics provide a complete background for this book, readers are referred to Appendix A for more comprehensive introductions to digital electronics.

In general, a logic gate may be thought of as shown in Figure 2.1. It has one or more inputs and one or more outputs, and requires +5 volts and ground. The inputs must be in one of two states (+ 5 volts or zero volts).

Memory is the second building block for measurement circuitry. In the parallel approach described so far, the maximum rate of data acquisition is determined by how fast the host computer can poll for data ready, input 1 or 2 bytes, carry out housekeeping operations (such as determining when to terminate acquisition), and then resume polling for the next data. For the ADC circuit in Chapter 4, with the 20μsec ADC and a 12.5 MHz PC AT compatible using Microsoft QuickBASIC, the maximum rate of converting voltage and inputting and storing 8-bit values is around 2000 readings/second. The capability for faster rates is desirable. A way to accomplish this is for the hardware to temporarily store data in its own memory. Then, after acquisition, the values are read by the host computer. This chapter introduces a particular memory chip, shows how to interface it to the parallel ports, presents control software, and gives a detailed application. Later, Chapter 10 describes a fast voltage measurer which uses memory.

A memory integrated circuit contains a set of storage locations each with a unique address. To write a value to a location, the address is specified, the value is made available, and the chip is told to store the value. To read a previously stored value, the address is specified and the chip is instructed to make the value available. Memory IC's are characterized by the number of storage locations, the bit size of stored values, and the control protocol.

The 8K by 8-bit 6264 static random access memory has been selected for temporary data storage. It is produced by several manufacturers and comes in a variety of models and speeds.