Make: Electronics by Charles Platt (classic books to read TXT) 📗

relay, can we use a transistor to switch on the rest of the circuit when the power is interrupted? Absolutely; in fact, one transistor will do it.

3. But how do we arm the alarm in the first place? Really, we need a three-step procedure. First, check a little light that comes on when all the doors and windows are closed. Second, press a button that starts a 30-second countdown, giving you time to leave, if that’s what you want to do. And third, after 30 seconds, the alarm arms itself.

4. If the alarm is triggered, what then? If someone forces open a window, should the alarm stop sounding as soon as the window is closed again? No, the alarm should lock itself on, until you turn it off.

5. How do you turn it off? Some kind of secret-code keypad would be good.

6. But to avoid driving everyone crazy if the alarm is triggered when you’re not there, it should eventually stop itself, perhaps after about 10 minutes. At that point it should remain quiet but should light an LED to tell you what happened. You can then press a reset button to switch off the LED.

Implementing the Wish List

I’ve compiled a wish list that seems likely to make the project at least five times as complicated as it is already. Well, that’s what tends to happen when you go beyond little demo circuits and try to design something that will be useful in everyday life. Suddenly you find yourself having to accommodate all kinds of circumstances and situations.

Actually, I can and will show you how to take care of all the enhancements on the wish list, but I’m thinking that they will require us to get a little more serious about electronics projects in general first. If you’re going to build something ambitious, you’ll want to make it more permanent, and probably more compact, than a breadboard with components pushed into it.

You will need to know how to connect everything permanently with solder, on a piece of perforated board that you can install in a neat little project box with switches and lights on the outside.

I’m going to deal with soldering and packaging in the next chapter. After that, we’ll get back to the alarm project.

Larger versions of all schematics and breadboard photos are available online at this book's website: http://oreilly.com/catalog/9780596153748.

Larger versions of all schematics and breadboard photos are available online at this book's website: http://oreilly.com/catalog/9780596153748.

Larger versions of all schematics and breadboard photos are available online at this book's website: http://oreilly.com/catalog/9780596153748.

3. Getting Somewhat More Serious

I don’t know how far you’ll want to delve into electronics, but I do know that I’ve shown you about as much as I can with just a handful of components, some wires, a breadboard, and a few tools. To continue, you’ll need:

Some more tools and supplies

Basic soldering skills

Additional knowledge about:

Integrated circuits

Digital electronics

Microcontrollers

Motors

The tools are not particularly exotic or expensive, and the soldering skills are easily acquired. Learning to join wires with solder is far easier than mastering high-level crafts such as jewelry making or welding.

As for additional areas of knowledge about electronics, they are no more challenging than those that I have covered already.

By the end of this section, you should be able to transplant components from a breadboard onto perforated board, where you will solder everything together, and then mount the board in a little box with switches and warning lights on the front, for everyday use.

Shopping List: Experiments 12 Through 15

Tools

Each of the following tools is rated Essential, Recommended, or Optional. The Essential tools will take you through this chapter of the book. If you supplement them with the Recommended tools, they should be sufficient to get you to the end of the book. The Optional tools will make your work easier, but whether they’re worth the money is for you to decide. Remember that URLs for manufacturers and sources of supply are all listed in the appendix.

I am assuming that you already have some commonly used workshop basics, such as an electric drill.

Essential: Pencil-type 15-watt soldering iron

Examples are RadioShack part 64-2051, McMaster-Carr catalog item 7016A34, or Xytronic model 252. See Figure 3-1. Soldering irons rated at 15 watts are less common than those that deliver 25 watts or more. Still, the 15-watt size is desirable for the small-scale work you’ll be doing, and greatly reduces the risk of damaging components by inflicting excess heat.

Figure 3-1. The low wattage of this pencil-style soldering iron enables you to use it safely on sensitive components, and the sharp tip helps to apply heat selectively.

When comparing prices, remember that a plated tip, which costs a little more, will last longer, will be easier to keep clean, and will conduct heat more reliably than a plain copper tip. If the manufacturer’s specification doesn’t mention a plated tip, the soldering iron probably doesn’t have one.

Essential: General-duty soldering iron, 30 to 40 watts

Although most of the projects in this book entail small, heat-sensitive components and thin wire, at some point you’re likely to want to make a solder joint with larger components and/or thicker wire. A 15-watt soldering iron will be unable to deliver enough heat. You should consider having a larger soldering iron in reserve, especially because they are relatively inexpensive.

Personally, I like the Weller Therma-Boost, shown in Figure 3-2, because it has an extra button that delivers more heat on demand. This is useful when you want the iron to get hot quickly, or if you are trying to solder very thick wire, which absorbs a lot of heat.

Figure 3-2. This higher-wattage soldering iron delivers the additional heat necessary for thicker wire or larger components. The discoloration quickly occurs as a result of everyday use and has no effect on the capability of the iron, as long as the tip of it is clean.

If you can’t find or don’t like the Weller, almost any 30-watt or 40-watt soldering iron will do. Check eBay or your local hardware store.

Essential: Helping hand

The so-called “helping