A WIZARD'S ELECTRONICS COMPANION
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A WIZARD'S ELECTRONICS COMPANION |
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This text was inspired by the remarkable efforts of my friend and wizardly mentor Krys in many disciplines, in an effort to teach him some electronics, just as he has endeavored to teach me programming. I write this for him, and anyone else who desires to be a jack-of-all-trades. This is an ongoing project. I make it freely available on the Internet, but it remains far from completion.
The electron is the most fundamental piece of the universe that we can perceive (with tools.) Anything smaller exists for us only as mathematical models based on truly bizarre experimental results from atom-smashers.
"All these fifty years of conscious brooding have brought me no nearer to the answer to the question 'what are light quanta?' Nowadays every Tom, Dick and Harry thinks he knows it, but he is mistaken" --Albert Einstein, 1951Electronics is the study and design of devices for the manipulation of electrons to perform useful tasks.
I have chosen a different sort of treatment of the subject, aiming toward the hobbyist or person who does not need a detailed, rigorous text but wants to know how to "do electronics". I will detail some of the most useful devices for the hobbyist and the conceptual tools to help understand and use them, the key technology to the many tools and toys we have today. After spending twenty years in the field I came to realize that most of the knowledge can be simplified a great deal and still get you through a project. Certain elements were common to most of my projects and I became obsessed with the idea of clearly communicating that core knowledge in a simple form similar to how I use it today as a hobbyist. This document is one more of my ongoing projects and will be updated occassionally. Email me at doncox@draigsffau.org if you have any thoughts for improvements you'd like me to mull over.
For an in-depth treatment of the subject in its current form, particularly for newbies, I highly recommend "The Art of Electronics" by Paul Horowitz and Winfield Hill, c1989 Cambridge University Press. The math is almost non-existent, preferring to give the reader a gut-level feeling for how it all works. For philosophy and heroes in electronics, "Analog Circuit Design" edited by Jim Williams, c1991 and published by Butterworth-Heinemann is an excellent read. It will help validate your thinking processes, and has many useful circuit ideas as well. "The ARRL Handbood for Radio Amateurs" is updated annually with pretty comprehensive theory and current radio laws and rules. "The Secrets of RF Circuit Design" by Joseph Carr will take you further into the ideosyncracies of high-frequency circuit design. The prolific writer Don Lancaster has several cookbooks, and a website at www.tinaja.com, full of useful information for the hobbyist and entrepreneur. For the sake of completeness, I will mention here an excellent and unique programming text called "Code Complete", published by Microsoft Press. The breezy, common-sense style makes it an easy read and the rules will stick with you. It is appropriate for any skill level. I need hardly mention that the World Wide Web gains useful electronics information daily at the price of a simple on-line search.
Advances in electronics and inflation have changed the landscape quite a bit over the years. Most surplus outlets have closed, and increasing complexity renders the utility of tearing apart a device for the parts impractical or impossible. When searching, don't overlook the small independent shops. Customer service will generally be better and they will usually order things they don't stock. Distributors built their businesses on the convenience of companies being able to obtain many different things from one source. Nowadays, most places have an Internet mail-order presence along with their brick-and-mortar offices. I've noted those businesses which are in the greater San Francisco bay area.
There are some fantastic computer software packages available that will allow you to simulate and test the operation of your circuit. For example, here is a delightfully long list of electronics software packages.
They can simulate more electronics than the average hobbyist will ever bother to learn (and do it quickly with virtual parts that you might not have handy.) Even if you choose not to buy one of these modeling tools, I list below a number of free modeling programs. The engine behind most electronic modeling is called Berkeley SPICE, a graduate project from a couple decades ago is available for whatever platform you're running (I've got a port of it on my old Amiga 2500 computer.) Because of the complexity of the field, many manufacturers also produce software which aids engineers in locating and analyzing their products, particularly as the SPICE models for an electronic components (in order to achieve any real accuracy) is difficult and expensive to put together. One simple component can have half-a-hundred variables describing various arcane parameters that have been mathematically modeled. For our purposes, we mostly just care about the primary ones--like the resistance of a resistor, ignoring the accuracy of the value, power capacity, temperature coefficient, stray inductance, stray capacitance, peak current capacity, etc.That said, I should probably mention the caveats to computer simulation: (1) A model is not reality. (2) Computer parts are perfect. Sometimes it is the little imperfections of reality that allow a circuit to work in the first place. (3) A demanding specification may exceed a model's range. These simple facts can drive a newbie crazy trying to get the simplest circuit to simulate properly. If you intend to use SPICE a lot, it is important to gradually learn what its capabilities and limitations are. WinSpice or SPICE Opus is a good place to start because they are fairly straightforward ports of the old Berkeley SPICE and this forces you to see and learn what the simulator is using for input. CircuitMaker is good if you just want to get to simulating simple circuits.
Here are the best freebies I could find that would work on my Windows 98 machine. In general, I have avoided the programs which run into the four figures as being too much for the beginner and too limited in function.
Bitmap drawing I still very much use. There are many tools available, the formats are common and standardized, drawings can be freely exchanged between programs, and the interface is familiar to anyone who uses a bitmap drawing program. Here are my old Amiga bitmaps (.png): and some vector symbols I later drew using Greenstreet Draw converted to bitmaps (.png). Many programs allow one to pick up portions of the screen after rectangular selection using either copy or move tools. When this is combined with a scalable snap-to grid, and the ability to paste at the cursor, you have a simple tool that is a pleasure to use.
Vector drawing takes the bitmap idea to the next level when symbols are scaled to fit a snap-to grid. Unfortunately, the world of objects is rather more complicated than the world of bits, so a multiplicity of formats and a dearth of compatible products abound. Here are my old Greenstreet Draw (.art) symbols, and in Postscript (.eps) format. There are a number of ways to get your foot in the door for free--see my CAD Programs page for reviews and tutorials for a number of those, particularly if you are still using Windows 98.
Diagram software takes the vector idea one step farther with the idea of "sticky-lines" that stretch, shrink, and move with the object you are moving. Check out Eve (Web Edition), Jan's Diagrams, and Dia on my CAD Programs page, particularly if you are still using Windows 98.
CircuitMaker (Student edition, Protel Technology, Inc., v6.2c) is fairly popular with newbies because of its relatively simple interface. A brief tutorial here, and a nicely detailed Wiki. It is intended for schematic capture for SPICE circuit simulation. The library component selection window is really nice for its use of automatically displaying subcategories, which greatly speeds part selection. For pure drawing purposes, the symbols are not quite the way I prefer them.
SPICE Opus: A free Berkeley SPICE port which allows up to 300 nodes. Raw SPICE with a DOS-like command window and graph windows for output. The best way to learn the nuts and bolts of SPICE.
WinSpice: A Berkeley SPICE port which uses the classic DOS-like interface and netlists. This is SPICE in its most raw form. I found that having to type in a text netlist of my simple circuit experiments really wasn't all that awkward--you learn to draw your simple circuit on paper and number your nodes and parts as appropriate, so typing it in is straightforward. An excellent learning tool to get a feel for the technical stuff behind all these simulation packages. If you wish to understand electronic simulation, and the omnipresent Berkeley SPICE which forms the basis of most of the software out there, working with netlists is a must. If you just want to draw a circuit and simulate it in a Windows interface, then this one is not for you.
Micro-Cap Schematic capture and SPICE simulation only. Free demo package limited to 50 components and does not allow some of the more powerful functions like multi-component optimization. Drawing is a pleasure with basic components on main toolbar (right-click during paste to rotate part), and menu Options=>Component Pallettes. Properties window appears automatically; for simpler parts, simply enter value and click Okay. Can add to the libraries, but is very confusing. My current favorite for SPICE simulation. Includes export functions to create netlists for several popular packages for PCB layout (Protel, Accel, OrCad, and PADS.) Other output options are native, but can turn off grid and screen-capture, as well as print to a Postscript file and convert to bitmap using GhostView and GhostScript and pressing f-key (convert) and selecting PNGMONO, DPI resolution, OK.
5Spice Analysis which works with WinSpice: Some limits in demo. $169 registration unlocks the fancy features. Demo version free. Has a nice schematic capture interface and parts are very easy to get access. Coincident part connections are not automatically wired. Rubber-band on wires works pretty well. They make it easier to find models for the library with some website links. AC, DC, Transient Analyses.
SuperSpice Symbols fairly easily accessible, as is more common among simulation programs. There is visual feedback when wiring components. Components must be specifically wired together--will not automatically rubberband if points are coincident. Adding models is fairly easy. Demo version free. Pro version US$340. Was unable to find SPICE engine to run simulation. Takes about 10 seconds to load, 10s to quit.
TopSPICE: Free demo version of a fairly pricey package. Limitations of the demo clearly stated. Looks like it could be good, but I haven't had a chance to check it out.
TINA Pro: Free demo, unknown limitations. Intended for a teaching environment. Can purchase an integrated separate box to digitize real-world signals and input them to TINA. Have not tried.
PSpice 9.1 Student version is well worth a look.
SIMetrix/SIMPLIS Intro: Mixed mode simulator. Demo has only some size restrictions. SPICE libraries handled.
TinyCAD is one of those delightful SourceForge finds released under the LGPL (a limited form of the General Public License.) It is only for schematic capture, and produces a netlist. Unfortunately, they have chosen to use Microsoft Access database format for the libraries. The obvious problem is already apparent in the help file where they mention upgrading libraries to the new Access format. A data format must be both stable and open for proper ownership. Using a proprietary "black box" format which is frequently altered puts the effective ownership of your data in the hands of the company that controls "access" to that format. Microsoft will frequently alter their formats to control compatibility with their software as a market control maneuver. This program is not recommended.
Rimu Schematic has a decent schematic capture interface except for polylines (default lines are unconnected segments.) The component selections includes a series of hierarchical windows which speeds process. Also, toolbar includes several pop-up windows with generic components. Program can be connected somewhat to simulation and layout tools tools which can use the output, though they must be added and specified. There are other programs I like better.
PCB Artist is another free package from a PCB manufacturer. Somewhat newer, it includes a rather nice autorouting feature in addition to both schematic and board editing. Like so many others with countless enormous libraries, access to simple components can be awkward. The solution is often a custom library of parts you actually use. Building custom library was surprisingly straightforward, and they include a link to a tutorial PDF in the library browsing window. Conversion to ratsnest was menu Tools >> Schematic<->pcb >> Translate to PCB, PCB wizard... 3rd screen ("Layers") you would select single-sided routing here by deselecting Bottom Side next to "Allow Routes" (ignore "2 layer board" listing"). In 4th screen ("Board Parameters") select your reasonable "Min. Track Width/Gap" value. In the "Production" screen, you can actually see their automatic price quote, if you were to choose to order boards from them (you can jump around the various screens and see how other values affect price.) Move on to the "Place and Route" screen. You will probably want to keep the selection "Arrange outside the board" as the program will not place them intelligently. In the "Finish" screen enter your save file name. The board window will now open, showing your board rectangle in green (you can resize it at any time by selecting and dragging sides and corners. The ratsnest will be above this. Drag components onto board. R-key will rotate symbol 90°. When you are done with placement, select "Route All Nets" tool at left or from Tools menu. Select "View Routes" because it's cool to watch. If it fails and you see a route, you can drag a pin route manually. Then, when you Route All Nets again, choose the "Keep Preroutes" option in the pop-up window. Save file. If you don't want to just print it or order boards, you can extract it via a Postscript printer driver with the "Print to File" option checked. The Postscript can be converted to, for example, a bitmap with GhostView and GhostScript by loading *.prn Postscript file, pressing f-key (convert) and selecting PNGMONO, 600, OK.
ExpressPCB and ExpressSCH: Free schematic capture and layout programs. Makes it easy to order boards from the company. Makes it hard to get your work out any other way; screen capture for the finished board was the only alternative to ordering as the output bmp file was always totally black and Postcript print file included grey background (manageable) and black square grid points all over it (nearly impossible). Easy to learn to use. Can create new parts for the library fairly easily. The main benefit (because it is only one step above simply using straight bitmap or vector symbols) is the ability to link the schematic with your layout and highlight each node (or net, as it is sometimes called.) A good starter package.
PCB123: Another PCB prototyping company. The free schematic and layout programs are slightly more awkward than ExpressPCB, but it includes a rather powerful autorouter function, as well as some other features I haven't yet explored. It is possible to output both PCB layout and schematic as PostScript files readable with GhostScript/GhostView (allows vector conversion to bitmaps, which are easily printed at copy shops with computers, to make your artwork.) I went to the Adobe site and downloaded their driver installer utility as well as a Postscript driver. For printing, check the print-to-file option. For you final layout output, you need to select just one layer with the layers toolbar, turn off the grid and pin numbers at the settings toolbar, and turning off net names in settings=>preferences=>general=>display tab=>net names checkbox in order to see just the trace artwork you want on that copper layer. Postscript will render it in nice clean vectorized black and white. This is my current layout package.
FilterPro: (If this link fails, try typing FilterPro in the keyword search box on the Texas Instruments homepage. The page on which it can be found in the returned list will likely be under "Amplifiers and Linear - Engineering Design Filter Utilities".) Limited to high- or low-pass filters (you must cascade them to make your own bandpass solution), but is a quick design wizard and gives you results as generic op amps instead of proprietary chips.
SwitcherCad3: A free schematic capture, SPICE, and netlists in and out. Models Linear Technologies products, but has basic components like resistors and capacitors, and plenty of examples. Finding a part is unnecessarily confusing. The choice to focus on SPICE and eschew simple mouse clicks was a bad idea as a schematic change which negates a SPICE run could easily be flagged on-screen, and the loss makes the interface a bit clunkier. For all that, it is still very worthwhile and remarkably powerful. FilterCAD is another free program from them which is a powerful filter wizard. The only drawback is that is renders everything in terms of Linear Technology chips. For all that, though, I was able to design a filter in just a couple of minutes with the specs I needed (as long as they had a chip that could handle your specifications.)
Eagle: Demo version limited by board size, but is fully functional for schematics, PCB layout, etc. Very powerful, but I have not yet gotten beyond the awkwardness of the part selection interface. Can autoroute single-sided PCBs. Free size is up to about 4x3 inches.
CirCAD: Schematic and PCB design. Looks promising but haven't yet tried it. Some reviewers find the interface a tad clunkier than some.
WinSchematic: This and a host of related products have demos which have nominal restrictions as stated on their FAQ page. Looks intriguing, but have not yet tried.
WinSchema: Intriguing and pretty low cost.
ORCAD is huge. I had to create a separate gigabyte partition for it. It is very powerful and includes schematic, layout, and simulation. The interface is complex, with design projects shown in a separate window in a hierarchical tree structure. It is clear that one could do a lot with it given enough time. To my mind, the Berkeley SPICE engine thumbs its geeky nose at this juggernaut which is a thousand times larger. I might grow to consider using it after a couple more years if I continue to use SPICE a great deal. Not for the faint of heart. To its credit, it is not a hobbyist package, but a full-blown professional one. One of the great features of high-end packages like this is their ability to easily download and install SPICE models directly from the component manufacturers--a much faster and more accurate way to simulate and build a design. I don't recommend the big, professional packages (like OrCad, Protel, Tango, and a couple others) for the hobbyist or small project shop.
McCAD didn't work for me. The interface was unpleasant to my eye and after a bit of fussing and hacking around I couldn't get the thing to do anything without reading the instructions--no demos, nothing. It is intended for layout with CAM output in the form of Gerber files and stuff, which is potentially quite useful as these tools are somewhat rare for hobbyists. It has a Gerber file viewer.
PCB Editor: A basic editor. Save disabled in demo mode. Can print to Postscript with appropriate driver installed. Roughly US$100 for standard and $200 for pro versions. About 4MB installed. No uninstall for demo. Not a good choice for free hobbyist work.
Like any field, electronics has its unique hazards. Probably the most common is a hot soldering iron. Whenever you get burned this way, the faster you can get some water on it, the better. I've successfully re-hydrated a lot of singed fingers this way. After fifteen minutes or so, you might have got lucky, and won't suffer the sting of a healing burn. Be careful of breathing soldering fumes, which may have lead, tin, resins, and a few other 'ickies', and absorbing the fumes and smoke through the mucous membranes of the eyes. Always wash your hands after handling solder, or lots of tinned components, with hands that might rub eyes, mouth, or food. There are non-lead solders available now which will help, although tin is still pretty poisonous. When I am etching copper-clad circuit boards, I try to avoid organic chemicals and hydrocarbons, anything exotic. I generally buy pre-sensitized circuit boards to avoid working with some of the nastier chemicals. If in doubt, any place you buy chemicals is supposed to be able to obtain a 'Material Safety Data Sheet' (MSDS) for a chemical product for you on demand, but nowadays there are excellent resources also online. Companies are supposed to keep a notebook full of MSDS for safety for all chemical products they use, which is very important when an employee splashes some chemical in their eye. Absolutely everything around us will get into our bodies to some degree, because we are intimately connected to our environments. The critical questions I ask myself frequently, even about the plastic computer screen I'm staring at right now are:
Unfortunately, the realities of the business world will render information about possible toxic effects of many substances difficult or impossible to obtain simply because it would open too huge a liability for companies and governments worldwide. It is up to you to educate yourself, and much of it is out there on the Internet. The deeper you dig, the more you will be horrified, but it may help you from becoming a statistic.
The zaps you get from static electricity around the house can be devastating to modern electronics. There will be a microscopic crater where you zap something which can be quite large in a microcircuit. Any insulating material is a potential hazard. A charge can be generated by physically rubbing or separating objects, heating a cup of coffee, allowing an ungrounded tip of a soldering iron to heat up, pulling a piece of transparent tape off a roll, a person walking, or someone even sliding a bit in their chair. Grounding things only provides a common reference potential, but the circuit is damaged by moving charges that are attempting to equalize to each other too fast or forcefully. The trick is to slowly equalize static charges over yourself and your equipment. Touching the computer case is fine for equalizing your body's charge to that of the case, but a computer board in a bag should be handled while you do so for several seconds before removing the board. Companies use anti-static mats and wrist straps to provide a common ground for this activity. Sprays can be purchased which can be used on carpets and chairs. Some diluted diswashing detergent left on a surface will be static dissipative. One common antistatic plastic in use in the industry is the classic pink tint of 'Pink Poly' bags and packing foam, others have a silvery tint. I now have an anti-static mat, but I keep anti-static bags around for work, too. If you must hand a sensitive part to someone directly, touch their hand just before placing the part there. Think of it like being in a lake where someone has just opened a floodgate over the dam -- you will want to be at the opposite end of the lake to avoid damage.
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