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Design007-Feb2020

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50 DESIGN007 MAGAZINE I FEBRUARY 2020 with a built-in speaker; therefore, the games didn't have any sound effects. To remedy this, I would grab a standard, portable AM radio off the shelf and set it up next to the computer while playing a game. The TRS-80 had a big problem, though—it radiated a lot of electro- magnetic interference (EMI). The effect was so pronounced that it would produce a buzzing over the radio's speaker that would vary in in- tensity and volume, depending on how active the computer was. For a game, this worked out better than you might think, and it is per- haps the only time in my life that I can think of where I used an EMI problem to my advan- tage. According to Wikipedia, the TRS-80 was actually discontinued primarily due to strict- er FCC regulations on radio-frequency interfer- ence to other devices. As it turns out, I wasn't the only one using a radio to produce sound ef- fects out of that computer. I have no idea what the circuit board or boards for the TRS-80 looked like, or with what level of technology they were designed, but from the amount of EMI that was created, there is probably a lot that they didn't have. I would guess that the boards probably had as few lay- ers as possible to reduce their production ex- penses. This would be at the cost of adequate ground planes for clean signal return paths and shielding. I would also assume that the routing on those boards may have been optimized for production instead of signal integrity, or per- haps there wasn't any optimization at all, and the traces looped all over. Those would be my first guesses, but there are many other design details to consider, as well. These would range from the type of components that were on the board, how they were used, and how the cas- ing was constructed. Wouldn't it be fun to open up one of those old computers now just to see what made it tick, or rather, buzz? PCB layout has changed a lot over the years. Back in those days, the signal speeds weren't anywhere close to what we are dealing with today, and most of us had no idea how many design errors and EMI nightmares we were cre- ating by today's standards. Like the boards in the TRS-80, many of the PCBs I designed in those days would probably spray interference around like a yard sprinkler on a summer day if they were to be evaluated by today's stan- dards. Things are different now, and most de- signs that I am familiar with go through strict design control for EMI by the design team and the manufacturer. In addition, there is a lot of help available for designers to better under- stand EMI problems and how to avoid them in their designs. Some of this help includes the following: Tools The PCB design tools available to the user today are packed with features and function- ality, and more is being added every day. In addition, circuit simulators and signal analysis tools are now more powerful, as well as being more affordable than ever. All of this has re- sulted in these analysis tools increasingly be- ing integrated into the PCB design tools so that everyone has easy access to them. Information When I first started designing, any addition- al information that you wanted on a design subject would only be available in print, and I just didn't get to the library that much. To- day, you can easily search for information on- line and find scores of publications written on any given topic. You can also find various user groups online that are often eager to help and share their knowledge. Education The different venues for increasing your knowledge of design subjects continue to in- As it turns out, I wasn't the only one using a radio to produce sound effects out of that computer.

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