Electronic Construction from A to Z

"Everything you wanted to know about building stuff but were afraid to ask."
by
Marshall G. Emm N1FN/VK5FN

 [This series was originally published in "73 Amateur Radio" between November 1997 and February 1998]

The complete article is available in hardcopy from Morse Express

Part I 
(you are here!)
Part II 
Part III 
Part IV
Introduction
Basic Tools
Soldering 101
Un-soldering 101
Basic Tools Table
Basic Kit Building
Populating the Board
Cleaning Up
The Smoke Test
Resistor Color Code
Choosing an Enclosure
Tools You'll Need
Preparing the Enclosure
Creating "Panel Art"
Trouble-shooting Basics
Isolate the Problem
Find and Fix
A Horror Story
Conclusion

Part I

As the doctor said to the patient, "I've got good news and bad news." The bad news is all around us-- increasing prices, decreasing skills base, no more Heathkits... and if you want more, just pick up a newspaper. The good news is that you can still build a lot of useful ham radio equipment and you don't have to be an electrical engineer to do it. All it takes is the right tools, knowledge of a few "tricks of the trade," and the will to succeed. Oh yeah-- a bit of patience helps too! We're going to try to cover the whole topic here in enough detail for you to pick up a soldering iron and get to work on a real project. First we'll talk about the basics, things like tool selection and soldering, then we'll move on to middle-to-advanced techniques, and finally trouble-shooting the finished project and installing it in an enclosure. Along the way we'll build something useful, I promise. You're going to discover that building is rewarding, educational, and fun!

Before we start, let's look at a fairly obvious question-- why build something when you can buy it? There are several reasons for building (even if you only need one)--

These four factors will influence your decision to build something, and whether to buy a kit or start from scratch. The project that we will build together can be purchased as a kit or built from scratch-- virtually everything in this series will relate equally to either approach.

A Disclaimer, of Sorts

I'm in the business. My company, Milestone Technologies, sells some of the tools that I am going to recommend and also the kit that we're going to do as a project. I'd hate to think that you would think I'm writing this series to sell stuff, so I will make a point of providing an alternate source for each of those items that I sell. Making some of these things available to you from Milestone Technologies is a service which you are free to decline.

A Poor Workman Blames his Tools

A crummy violinist playing a Stradivarius is going to sound like someone scraping a horse's tail across a cat's gut. A great violinist can make a cigar-box violin sound like a Strad. Or to put it in more familiar terms, an unskilled ham will have trouble making contacts with a three thousand dollar rig and a beam on a 100' tower, while a skilled operator can work DXCC on a home-made QRP rig with a dipole. The point here is that skill is more important than tools-- investing hundreds of dollars in tools and test equipment is not going to make you a good builder or technician. The value of your tool armory will increase as time goes by, but the basic tools for electronic construction are relatively inexpensive, and all of them are available at your local radio parts store and by mail-order.

Let's talk about a two basic tool kits for electronic construction-- hand tools and soldering tools.

The hand tools are really simple at "entry level" but even basic soldering tools start to get into areas of complexity, so you may want to read the section on soldering before deciding what to buy. The recommendations are summarized in table 1, which shows suppliers part numbers for Radio Shack (RS)(1) and Milestone Technologies (MT)(2).

Hand tools:
 

Soldering tools: Your "work bench" is important too, although it doesn't have to be elaborate. A kitchen table or desk will do. Things to consider are light, ventilation, and access to mains power and ground.

When it comes to light, you simply can't have too much. Flourescent light is best for electronic work because it is "whiter" than incandescent light. Ventilation is particularly important when you are soldering, because the fumes from the rosin can be irritating or even harmful over time. You will need mains power for your soldering iron, and you will often need to connect things to a good electrical ground (the center screw in the AC outlet will do).

Other than that, all you need to worry about is a reasonable amount of clear space, and places for tools and components. If you are using a space that has other purposes (i.e. your kitchen table) it's easy enough to keep your tools and components in trays so they can be easily put aside when you are not working.

Soldering 101

Entire magazine articles, even books, have been written about soldering. So how can I hope to teach you to solder with a few paragraphs and illustrations? Easy. Soldering is not difficult, and the basics are easily within your grasp if you have the right soldering iron, the right solder, and a little bit of practice.

Practice is important, so if you are new to soldering please take the time to do some before we start on the project! You can practice on any old components and a bit of scrap circuit board material-- or skip ahead to un-soldering, remove a couple of components from a junk circuit board and re-solder them. Kit suppliers will tell you that 90% of all problems in kit building are a result of poor soldering-- how can that be if soldering is not difficult? Simple-- carelessness and ignorance. We'll fix the ignorance problem right now-- carelessness is up to you.

Soldering is a process of amalgamating metals to provide a good electrical connection.
Solder is a mixture (alloy) of two or more metals with a relatively low melting point, that will flow onto the surface of other metals creating a low-resistance electrical connection. Ordinary solder is not very strong, and you should never rely on solder alone to hold components together physically.

Rule #1: A good mechanical connection is
necessary before you solder!
The mechanical connection should be secure before you apply solder, and the parts should not be able to move in relation to eachother. The flux is vaporized by the heat of the iron and the vapors will clean the surfaces of any oxidation (often invisible to the naked eye), allowing the solder to flow freely onto the metal surfaces.

The purpose of the soldering iron is to transfer heat into the work to be soldered; the solder should melt upon contact with the work. The iron must be at the correct temperature to do this, and some elementary principles of thermodynamics are involved here.

Rule #2: Strike while the iron is hot!
Fortunately, we don't have to worry about the details too much-- a 15-30W iron will heat up to an appropriate temperature and won't get too hot under ordinary circumstances. But let's look at the basics anyhow, because they will help you to understand what is going on, and also influence your decision to buy a temperature controlled soldering iron later!

The wattage of an iron is a measure of the power that is used to generate heat. Your soldering pencil is always running at that level of power consumption, and it is always generating heat. The tip has a specific mass which can absorb heat. As long as power is supplied it will continue to get hotter until it reaches equilibrium-- at its maximum temperature heat will be conducted away from it (into the surrounding air) as quickly as it is generated by the applied power. Heat will transfer out of the tip more quickly when it is in contact with the work, and the rate at which that occurs will depend on the size and shape of the tip, the amount of its surface that is in contact with the work, and the nature of the work (how quickly heat is conducted away from the point of contact). When your soldering pencil is sitting idle it very definitely gets much hotter than required for soldering, but it cools down almost instantaneously when you apply it to the work, and the applied power sustains the working temperature. When it's idle though, at higher temperatures, its surface is much more susceptible to corrosion. So turn it off when you are not actually soldering (for more than five minutes or so). Otherwise, you can expect to replace or refinish the tip fairly frequently. Leaving it on overnight once will ruin the tip. Once the tip has been overheated and cannot be tinned (see below) you can file or grind it down and start over, but it is usually a lot easier just to replace it.

All else being equal, the wattage of an iron is a poor indicator of its performance because it's main effect is in how quickly the iron will heat up to its maximum equilibrium temperature, or how fast it will create new heat for transfer into the work, and not necessarily how hot that temperature will be! That's why the best irons, if somewhat more expensive, are temperature controlled and not "variable output." I finally worked that out for my self after going through perhaps a hundred soldering iron tips.

From this point on, I'll be talking about soldering components onto a printed circuit board, but the principles apply to other soldering such as wire connections to controls.

Allow the iron to heat until solder flows freely on the tip, "tinning it." This means there should be a thin, shiny coating of solder on the working surface of the tip-- it should not "ball up" and drop off. Apply a small amount of solder to the tip and then wipe it off quickly with a soft cloth or a damp sponge. You can probably do three or four joints in immediate succession without having to repeat this process, but if you stop soldering to place components on the board you will need to repeat it.

Here are the steps in soldering a component into a circuit board:
 

That's all there is to it. And with practice, you won't even need to think about the steps as you go through them. There are variations and some specialized techniques that will be helpful later, but usually they are self-evident, and we'll mention them when we come to them in the course of building our project.

When you've soldered all the components onto the board, check everything again-- component values, orientations, and above all look for solder bridges and cold joints! When it comes to the latter two, it may be a good idea to remove excess solder flux from the board, but don't bother with that unless you really need to-- in my experience more problems are caused in the process of removing flux than are solved by it. If you do need to remove flux, use acetone or a commercial flux remover, in a well ventilated area. If you have invested solder with a water soluble flux, you will use water, of course, but do make sure the board is thoroughly dry before applying power to it!
 

Un-Soldering 101
 

For the most part, anything you can do with solder you can undo, if you know what you're doing. The secret is "solder wick," a fine copper braid impregnated with flux. Used properly, it can remove virtually all of the solder from a connection and a component, even an integrated circuit chip, will just fall out. A lot of people seem to have difficulty with it though-- it's one of those things where it's hard to figure out how to use it by yourself. One big problem is that solder wick should be marked with a "use by" date! The braid itself can oxidize over time, and the flux can dry out and fall out of the mesh, making it practically useless. So use fresh solder wick, and do it like this.
 


If you have trouble, remember that the two secrets are fresh solder wick, and plenty of heat!

To repair (remove) a solder bridge, apply the wick to the bridge and the solder should be removed from the board between the two pads-- you may need to resolder the connections, though.

Next month we'll build our project-- in the mean time you can get your tool kit together, practice soldering, and order a kit. It's the VM-110 AC Voltage Monitor from Electronic Rainbow , and if you don't want to order the kit you can find most of the parts pretty easily-- a list will be printed next month along with the schematic. The VM-110 kit costs $10.95 and you can order the complete kit or just the circuit board from Electronic Rainbow(3), or the complete kit from Milestone Technologies.


Table 1A: Basic Hand Tools(4)
Item Supplier Price Part Number
Long Nose Pliers RS 3.99 64-1844
Cutting Pliers RS 3.99 64-1833
Screwdriver, reversible RS 2.69 64-1950
Jeweler's driver combo set RS 4.79 64-1959
Hobby Knife RS 1.49 64-1805
Magnifying Glass RS 5.99 63-848
OR Jeweler's Loupes Set(3) MT 7.95 35450
Multimeter, 8-Range Analog RS 14.99 22-218
OR Multimeter, 14-Range Analog MT 9.95 30812
Clip Lead Set (10) mini aligator RS 3.99 278-1156
Sheet-metal Nibbling Tools RS 10.99 64-823
OR Heavy Duty Nibbling Tool  MT 9.95 00539
Table 1B: Basic Soldering Tools
15-Watt Soldering Iron RS 7.99 64-2051
Replacement Tip for Above RS 0.99 64-2052
Solder, 60/40 rosin core .032" 2.5oz RS 3.79 64-005
Desoldering Braid RS 2.29 64-2090

 

1. Radio Shack-- call (800) 843-7422 for location of nearest store, or to order by phone.

2. Milestone Technologies, 10691 E. Bethany Dr., Suite 800, Aurora, CO 80014-2670  (303) 752-3382, orders (800)238-8205 email: sales@mtechnologies.com, http://www.mtechnologies.com

3. Electronic Rainbow Inc., 6227 Coffman Rd., Indianapolis, IN 46268 (317)291-7269.

4. Prices were current published retail at time of preparation but subject to change


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