Make: Electronics Charles Platt (smart books to read txt) 📖

you press it. They are almost always SPST pushbuttons designed for mounting in circuit boards with standard 1/10-inch hole spacing.

12-key numeric keypad

Velleman “12 keys keyboard with common output” (no part number, but has been available through All Electronics under catalog code KP-12). Quantity: 1.

This type of keypad has the same layout as an old-fashioned touchtone phone. It should have at least 13 pins or contacts, 12 of which connect with individual pushbuttons, the thirteenth connecting with the other side of all the pushbuttons. In other words, the last pin is “common” to all of them, and this type of keypad is often described as having a “common output.” The type of keypad that you don’t want is “matrix-encoded,” with fewer than 13 contacts, requiring additional external circuitry. See Figures 4-10 and 4-11. If you can’t find the Velleman keypad that I suggest, look carefully at keypad descriptions and photographs to make sure that the one you buy is not matrix-encoded and has a common terminal.

Alternatively, you may substitute 12 cheap SPST NO pushbuttons and mount them in a small project box.

Figure 4-10. When shopping for a numeric keypad, it should have 12 keys in “touchtone phone” layout, and should have at least 13 contacts for input/output. The contacts are visible here along the front edge.

Figure 4-11. This keypad has insufficient pins and will not work in the circuit in this book.

Background

How chips came to be

The concept of integrating solid-state components into one little package originated with British radar scientist Geoffrey W. A. Dummer, who talked about it for years before he attempted, unsuccessfully, to build one in 1956. The first true integrated circuit wasn’t fabricated until 1958 by Jack Kilby, working at Texas Instruments. Kilby’s version used germanium, as this element was already in use as a semiconductor. (You’ll encounter a germanium diode when I deal with crystal radios in the next chapter of this book.) But Robert Noyce, pictured in Figure 4-12, had a better idea.

Born in 1927 in Iowa, in the 1950s Noyce moved to California, where he found a job working for William Shockley. This was shortly after Shockley had set up a business based around the transistor, which he had coinvented at Bell Labs.

Noyce was one of eight employees who became frustrated with Shockley’s management and left to establish Fairchild Semiconductor. While he was the general manager of Fairchild, Noyce invented a silicon-based integrated circuit that avoided the manufacturing problems associated with germanium. He is generally credited as the man who made integrated circuits possible.

Early applications were for military use, as Minuteman missiles required small, light components in their guidance systems. These applications consumed almost all chips produced from 1960 through 1963, during which time the unit price fell from around $1,000 to $25 each, in 1963 dollars.

In the late 1960s, medium-scale integration chips emerged, each containing hundreds of transistors. Large-scale integration enabled tens of thousands of transistors on one chip by the mid-1970s, and today’s chips can contain as many as several billion transistors.

Robert Noyce eventually cofounded Intel with Gordon Moore, but died unexpectedly of a heart attack in 1990. You can learn more about the fascinating early history of chip design and fabrication at http://www.siliconvalleyhistorical.org.

Figure 4-12. This picture of Robert Noyce, late in his career, is from the Wikimedia Commons.

Experiment 16: Emitting a Pulse

I’m going to introduce you to the most successful chip ever made: the 555 timer. As you can find numerous guides to it online, you might question the need to discuss it here, but I have three reasons for doing so:

1. It’s unavoidable. You simply have to know about this chip. Some sources estimate that more than 1 billion are still being manufactured annually. It will be used in one way or another in most of the remaining circuits in this book.

2. It provides a perfect introduction to integrated circuits, because it’s robust, versatile, and illustrates two functions that we’ll be dealing with later: comparators and a flip-flop.

3. After reading all the guides to the 555 that I could find, beginning with the original Fairchild Semiconductor data sheet and making my way through various hobby texts, I concluded that its inner workings are seldom explained very clearly. I want to give you a graphic understanding of what’s happening inside it, because if you don’t have this, you won’t be in a good position to use the chip creatively.

You will need:

9-volt power supply.

Breadboard, jumper wires, and multimeter.

5K linear potentiometer. Quantity: 1.

555 timer chip. Quantity: 1.

Assorted resistors and capacitors.

SPST tactile switches. Quantity: 2.

LED (any type). Quantity: 1.

Procedure

The 555 chip is very robust, but still, in theory, you can zap it with a jolt of static electricity and kill it. Therefore, to be on the safe side, you should ground yourself before handling it. See the “Grounding yourself” warning on page 172 for details. Although this warning primarily refers to the type of chips known as CMOS, which are especially vulnerable, grounding yourself is always a sensible precaution.

Look for a small circular indentation, called the dimple, molded into the body of the chip, and turn the chip so that the indentation is at the top-left corner with the pins pointing down. Alternatively, if your chip is of the type with a notch at one end, turn the chip so that the notch is at the top.

The pins on chips are always numbered counterclockwise, starting from the top-left pin (next to the dimple). See Figure 4-13, which also shows the names of the pins on the 555 timer, although you don’t need to know most of them just yet.

Figure 4-13. The 555 timer chip, seen from above. Pins on chips are always numbered counterclockwise, from the top-left corner, with a notch in the body of the chip uppermost, or a circular indentation at top-left, to remind you which end is up.

Insert the chip in your breadboard so that its pins straddle the channel down the center. Now you can easily feed voltages to the