Now that we’ve made it through a bit of the summer, I think we really need to focus on something important.

Winter is on the way!

If I recall correctly, my home is still not quite up to snuff in terms of how much money I’d like it to cost me to heat and energize my house. I realize my home will never be 100% efficient. I also realize I’m not going to plop down money to get to 100% because that’s silly and sort of impossible. Instead, I have to pick my battles with my own castle and decide what will produce the biggest returns.

1. Insulate
   • This is the number one project for the late summer/fall for me. I have very poor insulation in my upper floor. In fact, when we bought our house we could actually see the snow melting on the roof where the heat was escaping. Talk about watching your money fly out of your pocket! Check with a local contractor to see how much insulation you’ll need to really see some energy savings. Also, don’t forget the federal credit when you’re finally cutting that check…you could get up to a $1500 tax rebate.
   • But wait…there’s more! Don’t think that whole house insulation is the only thing to focus on. Oftentimes, the biggest culprits of letting expensive, hot air out (or in really) are the small cracks around windows and doors. Spending 40 bucks on some expandable foam, a tube of caulk, a water heater blanket and some new winterizing doorstops can go a long way.
2. Turn it off
   • There’s no denying that the most effective way to cut energy consumption is by turning devices and lighting off when not using it. This idea, coupled with using energy when it is cheapest and most abundant, is the crux of the “smart grid” idea. For devices that aren’t managed by a central management unit such as the one in the article, most devices now have a “sleep” mode that has reduced processing instructions; the device periodically “wakes up” to check to see if anyone has requested its services and if not it’s back to sleep. Devices with low quiescent current (or the current while not doing much of anything) can show large energy consumption savings.
3. Buy/Replace
   • Even though people probably don’t relish the idea of throwing away (or hopefully recycling) their old appliances, this is sometimes the best option. Your old freezer in the basement might be saving you trips to the grocery store (good) but might be doing it at the environment’s and your expense by increasing your electricity bill(bad). Pick up a Kill-a-Watt meter to see how much power your old junker is really pulling out of the grid; if it’s considerable, think about pulling the plug.
4. Inspect your ductwork
   • Oy, with the not-electronics already! I know, it’s not glamorous, but it’s often the simple things in houses that can really cost you. This is a big weakness in my house and something I will have to address before this winter. Back in the 50s and 60s they must have thought it fashionable (or at least cheap) to attach boards to the underside of the crossbeams of my floors. As such, the air actually being pulled down through the cold air returns is minimal, most of the air is actually pulled down through the floorboards and back into the cold air intake of my furnace. It’s a good time in the summer to check out where your ducts are leaking air so that you can save big dollars in the winter months.
5. Junk Water Dump
   • I saw an article a while back about the waste water from your tub also wasting energy. Think about how much natural gas/electricity it takes to get your water heater to temperature. Now think about how warm the water still is when it’s washed away all the nasty off your body. Finally, think about how cold the tap water can e in the winter. If you have a reservoir underneath your tub collecting warm wastewater and then coil the incoming cold water through it on the way to the water heater, you could possibly retain some of that usually wasted energy. Check out the link and check to see if you ever have that kind of option the way your house is set up. This could be the same for the dishwasher and the washing machine while the water is on “warm”.

I know you’ll see a lot of this information elsewhere but I’d feel silly not to encourage readers here to try it out for this coming winter. As I said above, there are many different monetary incentives to do so, both in rebates and power savings. I plan on getting the jump on these updates now so I can take advantage of the energy savings for cooling my house as well as heating it later on. If I find out about or come up with any other ways to save money and energy in the future, I’ll be sure to post them here.

What about you? Have you decided to do any updates to your home (energy-wise) while the weather is still nice? Do you have any tips you’d like to share? Just leave them in the comments!

Irony is having a blog post in your queue with a title such as this one and just sitting on it for weeks on end. Luckily I’ve been trying some things instead of studying them, it just so happens that those things have nothing to do with this site. I hope to discuss those on this site soon.

I am a glutton for knowledge.  Part of it is my fear of looking silly in front of co-workers when I don’t know the answer to something. Part of it is feeling like my knowledge base is lacking and the thought that I can always learn or teach myself something new. But when presented with a new challenging situation that requires you to learn the question is always the same: where do you start? Do you jump in and try it out? Or sit back and study what others have tried so as to not duplicate their mistakes?

There are two extremes

1. You study so much and try to take in so much that you become paralyzed by information
   • I feel like this happens to Generation Y more than other generations. Not because we are dumber than others. Instead, I think we are so accustomed to having all of the necessary knowledge required to solve a problem at our fingertips (i.e. Internet, ChrisGammell.com, etc).
   • Academic thought processes often begin with simplistic assumptions about the model you’re considering. Analyzing these over and over can be very time consuming and can quickly become too complex to handle. Even analyzing the minutiae associated with a single transistor can be mind boggling. What happens when you try and expand that knowledge to 10, 10k or 10M transistors?
   • You over simulate, over analyze, over think a problem past the point of diminishing returns. An example would be designing a new type of toothbrush. You can model the toothbrush, the bristles, the handle, the shapes, everything; you can even go out and get ideas from your toothy customers about what they think they would like or dislike about your design. But until you prototype your new type of toothbrush and put it through testing (product testing, tooth scrubbing ability, will it shatter in someone’s mouth), then all of the testing and surveying in the world won’t matter.
2. You have little knowledge of a problem or situation that you just start changing stuff randomly and keep changing until something works…without realizing the consequences.
   • This seems to be the modus operandi of the inexperienced, but not necessarily the uneducated. A gutsy, recently graduated electrical engineer may emerge from the cocoon of the academic environment ready to go out and change the world. And every resistor value of a circuit board they encounter. And mess with the capacitors. And change the model of the op amps. Oh, and don’t forget to swap out transistors. “What?? It still doesn’t work? But why?”
   • This can be as much a symptom of engineering bravado as it is bad conditioning. If the person involved has always had simple problems placed in front of them that have obvious or at least semi-obvious solutions (ahem, most introductory electronics labs), they will fix the “broken” component and pat themselves on the back. In the real world, that “broken” component isn’t broken at all. It’s just out of spec and you can’t figure out for the life of you why that unit you’re testing refuses to turn on anymore after increasing 5 degrees internal temperature.
   • You forget/refuse to read the manual. Granted, some of the greatest “tinkerers” out there can just magically turn a knob and get a broken piece of equipment to work. But the reason they can do that is because they actually turned the wrong knob about 1000 times the last time they tried to fix something like this and that knob did absolutely nothing.

A Good Mix (for me, at least):

[STUDY] My own personal mix when it comes to circuit problems starts with the problem definition. Understanding the problem is so much more important than what you study, how long you study it or how you begin to test out your ideas for how to fix it. If you don’t understand what the real problem is all that later work is for nothing! However, I try to understand the issue without going overboard and trying to understand every single minute detail; this could be just as bad as studying a possible solution for hours on end.

[TRY] Once I have a grasp on what the problem is, I try the obvious stuff. You’d be surprised how often it can be the really dumb things that trip you up. And those might not even be the problem you’re trying to fix. You could try to troubleshoot a blank screen for 20 minutes, throwing your best ideas and debugging techniques at it before you realize, “Whoops!” you never plugged in the display cable. Or you can’t get your software to work once you load it onto your electromechanical whizzbang toy…but you actually loaded the wrong version of the software or the toy doesn’t have any batteries in it. The silly things will waste your time and throw you off the trail of the real problem if you’re not careful.

[STUDY] Next is researching the problem to see if it has happened before. Some of you out there will have unique situations, like making a new analog chip that no one has ever made before. But I’d guess more of you will be encountering problems that can be researched. Even the analog chip designers will see issues that are similar on some level to other products or models within a corporation. Oftentimes the best troubleshooters are those who are able to compartmentalize problems and then analyze where those problems came from and research how others have fixed it in the past. I’d rather have a boring problem that someone else can easily tell me how to fix than one that I can’t figure out at all.

[TRY] After trying and then studying all of the really obvious stuff, I start to go back to my resources–either online or in print–and start to search for information on the topic. Obviously the online information is much easier to search, but I also have some trusted books that I turn to on a regular basis. I might see a chunk of a circuit that looks familiar and try flipping through the pages to see if I can’t find a similar circuit. If that doesn’t work or the circuit looks extremely foreign to me, I’ll go back and study some of the basic properties of the components within the circuit to see if there might be a certain property the designer used that I have overlooked. And if all else fails, I’ll start to ask around to try and gather others’ knowledge of the circuit. True, this isn’t quite studying, but can often be more effective. I try and balance asking others for assistance only after I have tried to solve the problem on my own and not made any progress. I think it is important for my personal growth to struggle with a circuit before asking for help and I think it’s important to not get in the habit of running off and asking for an answer so I don’t waste the other person’s time. However, I don’t want to be so stubborn that I waste my time and the time of those who are paying me.

[STUDY] Alright, so now you know what the circuit is and how it sort of works. But you also know that you need to change the circuit in order to make it work better. What now? Next I would try and write out any equations I know that are relevant to the circuit. Not necessarily any equation, that could end up being a waste of time. Keep it simple and make sure you know where the currents and voltages are in different parts of the circuit. If there are components (such as capacitors) in the circuit, include basic equations that can help to describe their behavior. If you don’t need 3 chalkboards to do so, try and figure out the transfer function (relationship from input to output). If you have a circuit that is too complicated either break it down into smaller pieces and try and figure out the transfer function or take the plunge and try it out in SPICE. This will help you to better understand how the circuit might behave when presented with certain inputs. All of these exercises are done in order to present you with a solid starting ground for when you actually construct the circuit, so you know what to look for and what behaviors to expect.

[TRY] After all of the studying and simulating and pondering about this circuit, you should have at least enough knowledge to begin building up and trying the circuit. This is an important step in any circuit creation process because of the nuances the real circuit will show you. Perhaps you forgot to model a realistic op amp in your SPICE simulation and it was outputting 500 A. Perhaps you didn’t realize in your equations that a resistor will have different properties depending on how much current you actually put through it and that your circuit happens to be particularly susceptible to those changes. Perhaps you completely disregarded a simple concept such as bandwidth and your circuit is now oscillating so hard it breaks. All of these things will be uncovered when you begin to build up your circuit and try out different inputs. Once you realize what some of the realistic problems are you can go back and modify your assumptions and models and start to delve into whatever topics you believe will get your circuit to the optimum operating point.

Finding the right balance between slowing down and taking your time to figure out a circuit or jumping in and seeing what works can be a fine art. Sometimes projects are on a very tight schedule and need a product cranked out the next day (think startup). Sometimes you have one shot at making a final product or else your company will fail (think chip fabrication). Finding your own personal mix will take time and trial and error.

What is your personal mix of trying vs. studying that gets the best results? Leave your tips and tricks in the comments!

I find myself sitting around these days trying to catch up on knowledge I feel like I missed in school. Worse, I feel like I learned it at one time but it all fell out the other side once I took the exam. Pretty standard really, when you don’t think you’re going to need to the knowledge some day. Haven’t you ever sat in class wondering if you’d really ever use the material you were expected to learn? How much did you pay attention?

I feel that a requisite of every college class should be at least an entire class devoted to how you can use the knowledge contained in the remainder of the course material. It should probably happen close to the beginning of the semester or quarter. I have always lobbied for this kind of explanation and have always tried to include it whenever I am teaching something. Better yet, if someone from the field come in and explain how they use the knowledge in their working lives it would really drive the point home. When you know that you will definitely use certain knowledge, you’re more likely to sit up and pay attention.

Some of the material that I have been relearning lately has been tangential to the actual material we covered in classes back in my school days. Some of this is because I needed to go back and re-learn the absolute basics, such as semiconductor physics. I didn’t quite need to learn why a PN junction behaves as it does, only how it behaves and how it relates to larger devices such as transistors (basically a couple PN junctions specialized for certain behavior and placed in a certain configuration). I also don’t need to know why certain materials carry magnetic fields, only how they do and how you can use them to build a transformer. Other than re-learning the absolute basics, it’s driven by things I encounter in my daily work where I feel I was lacking. Very general topics but things that have very specific application in my job. Transformers are an area where I felt it was necessary to get more info, so I used my favorite resource (OhioLink) to get some textbooks based on co-workers recommendations. Hey, you just end up reading the textbook in some classes anyway, right? So why not?

So I guess that’s all I have to say about this topic. If you don’t know something, go to the library and and figure it out (I love libraries). And if books don’t show you what you need, ask a friend. Most importantly, find out where you might use the material you’re learning the first time you see it. If you’re not being directly told why you will need a certain piece of information, do the legwork yourself and figure out why you should care (someone saying “because it’s in the course outline” isn’t good enough). The application of the knowledge is much more important over the long term.

Got something you can’t figure out? Ask me in the comments.

If you are an engineer who regularly works with your hands, you likely troubleshoot on a daily basis. It’s just part of the job. Sure, you can say, “I never mess up!”, but hardly anyone will believe you. Because even when your best laid plans go perfectly, Murphy’s Law will soon kick in to balance things out. We learn to deal with these things and have developed tools and measurement equipment to help us diagnose and deal with these problems: Multimeters, Electrometers, SourceMeters, Oscilloscopes, Network Analyzers, Logic Analyzers, Spectrum Analyzers, Semiconductor Test equipment (ha, guess I know a little about that stuff)…the list goes on and on. But what has struck me lately has been that as parts on printed circuit boards get smaller and smaller, troubleshooting is getting…well….more troubling.

1. Package Types — I don’t want to get into another discussion of analog vs digital, but I will say that digital parts on average have many more pins which complicates things. And as the parts get more and more complex, they require more and more pins. The industry solution was to move to a Ball Grid Array package, using tiny solder balls on the bottom of the chip that then line up with a grid of similar sized holes on the board. When you heat up the part the solderballs melt and hold the chip into place and connects all of the signals. The problem is the size of the solderballs and the connecting vias: they’re tiny. Like super tiny. Like don’t try probing the signals without a microscope and some very small probes. But wait, it’s not just the digital parts! The analog parts are getting increasingly small to accommodate any of those now-smaller-but-still-considerably-bigger-than analog parts. You thought probing a digital signal was tough before? Now try measuring something that has more than 2 possible values!
2. Board Layers — As the parts continue on their shrink cycle, the designers using these parts also want to place them closer together (why else would they want them so small?).The circuit board designers route signals down through the different layers of insulating material so that mutiple planes can be used to route isolated signals to different points on the board. So to actually route any signals to the multitude of pins available, more and more board layers are required as the parts get smaller and closer together. Granted, parts are still mounted on either the top or bottom of the board. But if a single signal is routed from underneath a BGA package, down through the fourth layer of an 8 layer board board and then up to another BGA package, the signal will be impossible to see and measure without ripping the board apart.
3. High Clocks — As systems are required to go faster and faster, so are their clocks. Consumers are used to seeing CPU speeds in the GHz range and others using RF devices are used to seeing even higher, into the tens of GHz. The problem arises when considering troubleshooting these high speed components. If you have a 10 GHz digital signal and you expect the waveforms to be in any way square (as opposed to sinusoidal) you need to have spectral data up to the 5th harmonic. In this case, it means you need to see 50 GHz. However, as explained with analog to digital converters in the previous post, you need to sample at twice the highest frequency you are interested in to be able to properly see all of the data. 100 GHz! I’m not saying it’s impossible, just that the equipment required to make such a measurement is very pricey (imagine how much more complicated that piece of equipment must be). High speed introduces myriad issues when attempting to troubleshoot non-working products.
4. Massive amounts of data — When working with high speed analog and digital systems there is a good amount of data available. The intelligent system designer will be storing data at some point in the system either for debugging and troubleshooting or for the actual product (as in an embedded system). When dealing with MBs and even GBs of data streaming out of sensors and into memories or out of memories and into PCs, there are a lot of places that can glitch and cause a system failure. With newer systems processing more and more data, it will become increasingly difficult to find out what is causing the error, when it happened and how to fix it.
5. Less Pins Available out of Packages — Even though digital packages are including more and more pins as they get increasingly complex, often times the packages cannot provide enough spare pins to do troubleshooting on a design. As other system components that connect to the original chip also get more intricate (memories, peripherals, etc), they will require more and more connections. The end result is a more powerful device with a higher pin count, but not necessarily more pins available for you the user/developer to use when debugging a design.
6. Rework — Over a long enough time period, the production of  printed circuit boards cannot be perfect.  The question is what to do with the product once you realize the board you just constructed doesn’t work. When parts were large DIP packages or better, socketed (drop in replacements), changing out individual components was not difficult. However, as the parts continue to shrink and boards become increasingly complex to accommodate the higher pin counts, replacing the entire board sometimes becomes the most viable troubleshooting action. Environmentally this is a very poor policy. As a business, this often seems to be a decent method (if the part cost is less expensive than the labor needed to try and replace tiny components) but if and when the failures stack up, the board replacement idea quickly turns sour.

While the future of troubleshooting looks more and more difficult, there have always been solutions and providers that have popped up with new tools to assist in diagnosing and fixing a problem. In fact, much of the test and measurement industry is built around the idea that boards, parts, chips, etc are going to have problems and that there should be tools and methods to quickly find the culprit. Let’s look at some of the methods and tools available to designers today:

1. DfX — DfX is the idea of planning for failure modes at the design stage and trying to lessen the risk of those failures happening. If you are designing a soccer ball, you would consider manufacturability of that ball when designing it (making sure the materials used aren’t super difficult to mold into a soccer ball), you would consider testability (making sure you can inflate and try out the ball as soon as it comes off the production line) and you would consider reliability (making sure your customers don’t return deflated balls 6 months down the line that cannot be repaired and must immediately be replaced). All of these considerations are pertinent to electronics design and the upfront planning can help to solve many of the above listed problems:
   1. Manufacturability — Parts that are easy to put onto the board cuts down on problem boards and possibly allows for easier removal and rework in the event of a failure. It becomes a balancing act between utilitizing available space on the board and using chips that are easier to troubleshoot.
   2. Testability — Routing important signals to a test pad on the top of a board before a design goes to the board house allows for more visibility into what is actually happening within a system (as opposed to seeing the internal system’s effect on the top level pins and outputs).
   3. Reliability — In the event you are using parts that cannot easily removed and replaced and you are forced to replace entire boards, you want to make sure your board is less likely to fail. It will save your business money and will ensure customer satisfaction.
2. Simulation — One of the best ways to avoid problems in a design is to simulate beforehand. Simulation can help to see how a design will react to different input, perform under stressful conditions (i.e. high temperature) and in general will help to avoid many of the issues that would require troubleshooting in first place. A warning that cannot be overstated though: simulation is no replacement for the real thing. No matter how many inputs your simulation has and how well your components are modeled, no simulation can perfectly match what will happen in the real world. If you are an analog designer, simulate in SPICE to get the large problems out of the way and to figure out how different inputs will affect your product. Afterward, construct a real test version of your board or circuit and make sure your model fits your real world version. By assuming something will go wrong with the product, you will be better prepared for when it does and will be able to fix it faster.
3. Very very steady hands — Sometimes you have to accept the fact that you messed up and the signal traces on your board and you have to rewire it somehow. My analog chip designing friends needn’t worry about trying this…chips do not have the option for re-wiring without completely reworking the silicon pathways that build the chip. In the event you do mess up and have to try and wire a BGA part to a different part of the board or jumper 0201 resistors, make sure you have a skilled technician on hand or you have very steady hands yourself. And in the event you find yourself complaining about how small the job you have to do is, think of the work that Willard Wigan does…and stop complaining.
4. On the Chip/Board tools — Digital devices have the benefit of being stopped and started at almost any point in a program (debug). Without being able to ascertain what the real world output values are though, it doesn’t help too much. If in the event you do not Design for Test and actually pull signals you need to probe to the top level then you create a board then there are a few other options. One option is to try and read your memory locations or your processor internals directly by communicating through a debugger interface. But if you are looking at a multitude of signals and want to see exactly how the output pins look when given a certain input there is another valuable tool known as “boundary scan”. The chip or processor will accept an interface command through a specified port and then serially shift the values of the pins back out to you. Anytime you ask the chip for the exact state of all the pins, an array of ones and zeros will return which you can then decode to see which signals and pins are high or low.
5. Expensive equipment — As mentioned above when describing an RF system measurement needs, there will always be someone who is willing to sell you the equipment you need or work to create a new solution for you. They will just charge you a ton for it. In cases I have seen where a measurement is really difficult to calculate or you need to debug a very complicated system, the specially made measurement solutions often perform great where you need them, but are severely limited outside of their scope. To use the example from before, if you needed a 100GHz oscilloscope, it is likely whomever is making it for you will deliver a product that can measure 100GHz. But if you wanted that same scope to measure 1 GHz, it would do not perform as well because it had been optimized for your specific task. However, there are exceptions to this and certain pieces of equipment sometimes seem like they can do just about anything.

Debugging is part of the job for engineers. Until you become a perfect designer it is useful to have methods and equipment for quickly figuring out what went wrong in your design. Over time you become better at knowing which signals will be critical in a design and planning on looking at those first, thereby cutting down on the time it takes to debug a product. And as you get more experience you recognize common mistakes and are sure not to design those into the product in the first place.

Do you know of any troubleshooting tools or methods that I’ve missed? What kinds of troubleshooting do you do on a daily basis? Let me know in the comments!

Analog. Digital. Continuous. Discrete. Choices abound.

Well, not really.

In reality you will deal with both kinds of signals when working on just about any electronics these days. A simple example is in a switching regulator. These devices are meant to take input power from a wall plug or something providing a relatively constant voltage and then the regulator will ensure that the voltage is always the same when leaving. Internal to the circuit, a “digital” signal (on or off) determines when to let in incoming power go from the input to the output. The “digital” signal translates into an “analog” voltage at the output, hopefully the voltage you programmed.

From there, systems become increasingly complicated, translating real world data to digital format, processing the digital data and spitting it back out again. The guts of the systems have infinite internal combinations and options, but in the end just about every hybrid system looks like this:

The remainder of this post will be devoted to explaining situations that are either contained within the above system or situations that benefit from looking nothing like it; some of these situations mandate analog or digital implementation but more importantly, some are best implemented as analog or digital.

To start, what is the definition of analog? We’ll consider it a continuous signal that has infinite bandwidth and complete spectral information. Analog in the context of this site usually refers to the circuitry used to operate on those continuous signals, but we also use the word “analog” interchangeably to describe the signals. Which situations are best suited to using analog components and circuitry?

1. Continuous filtering — Filtering a signal is necessary when it has frequency components included that you do not want. Some filters are digital and are extremely accurate at removing one signal while retaining others (FIR). However, if you are dealing with a continuous signal and you want to filter ALL possible frequency content (and not be limited by the sampling frequency you used when converting to digital), then you need a continuous analog filter. There are many options available that can also help to push your filtering towards accuracies similar to digital filters but they become increasingly complex (multi-pole active filters). The main advantage to an analog filter here is that it is simple, less expensive (usually) and beyond your roll-off frequency you know that all information is being removed (whereas it might still be hidden in a sampled signal).
2. Pre-A/D and Post D/A — Hybrid systems require both analog-to-digital converters and digital-to-analog converters to switch between continuous and discrete data. However, the sampling frequency must be at least twice the frequency of the highest frequency component contained within the signal, as explained by Nyquist’s Theorem. In order to ensure that the Nyquist Theorem is fulfilled, you can filter (see above) any signals that are inadvertently included in the original signal so that it does not create noise and artifacts after sampling. Since the signal is not yet digital, you HAVE to filter the signal with an analog filter (convenient, right?). Once you are done operating on a signal digitally and you convert it back to analog, all processing must once again be done with analog components and circuitry (see picture above). I usually think of an iPod after the signal has gone through the DAC. You need to control the gain (volume) and shape the frequency components (tone). Some post DAC activities can be done in the processor, but are often more efficient (read: cheaper) to do in simple analog components after the DAC.
3. High power — While digital measurement and control is possible for high power systems, having a digital signal that switches between 0 and 400V would not be efficient. In either AC or DC systems, analog components are responsible for transforming and transmitting signals (although there may be digital control of those analog components at some point in the system). The continuous nature of power delivery mandates analog components that are well characterized and durable.
4. Gain Control/Signal Conditioning — Say you want to measure the amplitude of a 4000 V signal. You decide that you want to use a computer to do so, so you shove your signal into an A/D converter. But wait, where the heck do you find an A/D converter that can convert a 4000V signal? Sorry, they don’t exist (yet). You instead have to condition the signal to fit into a range of 0V to +2.5V, or whatever is the input range of your specific ADC. You can do so with a simple resistive divider (passive, simple) or an inverting amplifier (active, more difficult).
5. Control systems — While digital control systems are possible and are becoming more and more prevalent, analog systems can be simpler. One of the simplest examples is an inverting op-amp configuration. The load of the op amp is the plant, the op amp is the controller and the resistors are the feedback paths to the summing node. There are some delays in the system, but in general, the signal can handle a wide range of frequencies without complicated circuitry and the system can adjust to however the input changes. In a similar digital system, the feedback resistor would be replaced with an ADC, some kind of computing machine (microcontroller) and a DAC to convert the data back to analog to push into the summing node. The system is dependent upon the technology and speed of the components, whereas the analog system is dependent on resistors and the nature of the load (plant). Digital control systems are becoming more popular as DACs and ADCs become faster and more accurate but as of now, analog control systems remain simpler in some of the more common instances.
6. Sensors — These devices are meant to help convert real world information that isn’t necessarily electrical, into a format that is recognizable by a computer or embedded system. Oftentimes these are not taking real world (analog) data and directly turning them into digital signals. Instead, the sensor (sometimes known as a transducer) first creates an analog signal that can later be converted. Converse to the high voltage systems, sensors are often very low amplitude and require some signal conditioning to increase the value of the signal to better utilize the full range of an ADC.
7. Fidelity/Data loss — Some people just love analog stuff, especially when it comes to music. Even though audio systems containing ADCs and DACs are making very good analog equivalents these days, you will have to tear the record players and the tube amps out of the hands of the most die hard audiophiles. So instead of converting back and forth between digital and analog media, they prefer to keep the signal continuous all the way throughout the process. Starting from the air pressure variations emitted from Louis Armstrong’s trumpet that are then captured by a microphone and then amplified and pressed into a record, then touched by a needle and amplified again by a transistor or tube amp to recreate the sound as it is pushed out of your high end speakers. And even though there are processes to mathematically capture all of the data that is present to sample and perfectly recreate the original signal, some people won’t touch the stuff. Since I can’t afford the high end equipment audiophiles claim is necessary, I will sit on the sidelines for this argument. However, I enjoy that there is still so much interest in preserving audio fidelity in analog formats and don’t mind that it keeps analog engineers employed.

I feel a little silly explaining digital advantages because they seem to be flaunted at every opportunity by media and digital chip makers. Still, let’s go over some of the more important places to use digital as opposed to analog.

1. Computing — Again, I know it sounds silly, but digital has emerged as the better way to compute numbers. How did they compute mathematical sums before the advent of the microchip and digital logic? Why, operational amplifiers of course! That is actually where the name comes from, since there are many different possible operations for incoming signals.  If you have two incoming signals, one at 2 volts and the other at 1 volt, you can: add them (summing amplifier), subtract them (differential amplifier), integrate them or differentiate them. While this can and still does work quite well on a large signal DC basis, using operational amplifiers in the computing machines today would be a bit unruly. Just to start the power usage and the offsets would pose enough problems to make you run out and buy ADCs, DACs and micro-controllers. If you have a big math problem to do, follow that urge. However, if you do have a simple math operation you need to do on two signals and you don’t want the overhead of a digital section, op amps can still do the trick nicely; with their fast reaction and the complete lack of sampling issues you won’t miss those ones and zeros for a second.
2. Counting — In analog systems, counting can be a difficult task. Instead, using integrators to “sum up” signals is a way to figure out where you might be in a process. Discretizing a signal and then counting how many times it happens can have many uses in control systems, measurement systems and a range of other applications.
3. Memory — Storing analog signals would be difficult. For even a simple 0-1V signal, you would have to be able to store an infinite number of values. If you have 4 bits to represent the range from 0 to 1 volt, then you instead only need 16 places to store values. In control systems and other places that require memory, the old way to “store” values was to sufficiently delay them and feed them back so as to combine them with a newer signal. Using memory now allows for interesting systems and use of state machines to determine what to calculate or execute next based on current and past input data.
4. High noise environments — If you are trying to transmit an analog walkie-talkie signal (5Vpp sine wave) in a field that happens to have a white noise generator transmitting (2V) at the same frequency you are using, it is likely that whoever is on the receiving end of that signal will also get a good bit of white noise in their signal (think static). If you instead use a digital signal (varying between 0 and 5V) your friend who has a digital transceiver will be able to discern your transmitted highs (5V) and lows (0V) even if they also have noise added to them. Once the digital data is received and decoded, the original signal (5Vpp sine wave) can be reconstructed on the receiving end.
5. Signals Transmission – As stated above, there are advantages to transmitting digital signals as opposed to analog. Most notable is the lower power spectral density of the digital signals and that less power is needed to transmit those signals. In current events, we see TV transmission changing from analog to digitla because of the lower power required to transmit the signal and the possibility for multiplexing signals on specific frequencies in order to get more channels transmitted in the allowable spectrum.
6. Data storage — To use the mp3 example again from above, data is best stored in a digital format (easy there audiophiles, records are alright for some people too). True, some information is lost, but only information above the Nyquist Sampling rate. In audio signals, most people cannot hear above 20 kHz, so there isn’t too much to worry about beyond that (perhaps the harmonics that some people claim to hear and desire in their recorded works).
7. RF — Digital Signal Processing (or DSP) is one of my favorite digital topics. There are so many cool things you can do with a Radio Frequency (RF) signal once it is sampled and put into a powerful processor. In fact, this process makes your cell phones and Wi-Fi connections possible. FIR filters, CIC filters, baseband shifting and so many other interesting topics make it possible. Hell, maybe some day I’ll start “Chris Gammell’s DSP Life“. Anyway, can’t we do this stuff in analog? Well yes, we can. But with RF, it comes down to precision. With the filters listed above, you can trade off processor time/power for a more precise filter. In analog systems, you instead need more and more precise components and increasingly complex systems to achieve similar results. In DSP there is also reconfigurability, either through logic rework (FPGAs) or coding (in DSP chips), so long term investment usually will favor DSP over analog RF solutions. Finally, there is more efficient use of bandwidth with digital systems, so you can shove more data into the same frequency space. All of these things have helped to push the RF areas towards digital processing.

I think one of the most interesting things when reviewing this list is that it’s possible to implement solutions in myriad ways. Oftentimes cost and tradition (or past work) determine which way a solution will eventually lean (digital or analog). And although I hope to expand upon it in future posts the most interesting thing to me is that analog and digital begin to merge at the extremes: do analog signals really exist if energy is explainable by quantum mechanics? Will digital signal continue to only have two logical states when there is so much data storage capacity available between 0 and 1?

Please comment on the above lists–right or wrong–and let me know a situation or two that you think benefits from analog or digital.