标签: life

Since we just recently entered a brand-spanking-new year, it perhaps behooves us to pause for a moment to contemplate the meaning of liff. What? No, I don’t mean the meaning of life. I'm talking about the book called The Meaning of Liff by Douglas Adams and John Lloyd.   Actually, I hang my head in shame when I admit that I had never heard of this little beauty before, even though the original edition was published way back in the mists of time we used to call 1983. (That's more than 30 years ago -- eek! ) I'm a huge fan of Douglas Adams, so I have no idea how this little scamp (the book, not Douglas Adams) slipped under my radar. The first I knew of it was when my little bro' gave me a copy of the "new and unimproved" edition for Christmas. This is such a clever book. It's a dictionary of things for which there currently are no words. The really clever part is that, rather than creating new words from scratch, the authors simply assign new meanings to existing place-names. Opening the book at random, for example, we find the following: Alcoy adj. Wanting to be bullied into having another drink. Berriwillock n. An unknown workmate who writes "All the best" on your leaving card. Clakavoid n. The technical term for a single page of script from an Australian soap opera. Dungeness n. The uneasy feeling that the plastic handles of the overloaded supermarket carrier-bag you are carrying are getting steadily longer.   Many of these are laugh-out-loud funny. Also amusing is the fact that each reader will find different entries to be funnier (or not, as the case might be).   In fact, this book has turned out to be very educational, because I've found myself using Google Earth on my iPad to locate and "visit" many of the more unusual place names.   Also very poignant is the back-and-forth dialog between the authors in the prefaces to the various editions. For example, the preface to the 1988 reprint reads as follows:   Did you get the preface I faxed you from New Zealand? -- Douglas Adams, Zaire, 1988   This is followed by the preface to the 1989 reprint, which reads as follows:   No. -- John Lloyd, Lambeth, 1989   Douglas Adams was born in 1952 -- just five years before yours truly. In addition to The Hitchhiker's Guide to the Galaxy , he also wrote such classics as Dirk Gently's Holistic Detective Agency and The Long Dark Tea-Time of the Soul . He passed away from a heart attack in 2001 at only 49 years of age.   Like so many other people, Douglas Adams was cut down before his time. The scary thing is that any of us could shrug off this mortal coil at any time. All I can say as we stand at the beginning of this new year is that life is very, very precious, and that we should all do our best to make the most of it and to help others make the most of it also. So let's all go forth and make the world a happier place!

I am crazy. At least my wife thinks so. She has been watching me discharging piles of coin cells over the last year, collecting millions of data points about their behavior. “Honey, exactly why are you spending all that money on batteries you’re just going to discharge?” It is pretty nutty, but the results are interesting, and dispel a lot of beliefs about what we can expect in long-lived, ultra-low-power, microcontroller-based products. I previously wrote about the behavior of CR2032 coin cells in applications that have to run for a decade or so. My experiments quantified the batteries’ increasing internal resistance as they’re used. The net result is that, depending on the system’s current needs, the cell will appear dead long before it really is. That is, there will be plenty of capacity left, but none of it will be useable by the system. Several thoughtful readers wondered if adding a capacitor across the cell’s terminals could provide a short-term boost that could sustain a pulse load. It’s not hard to show mathematically that the answer is “yes.” But the math is irrelevant. In engineering we’re always faced by conflicting needs and what appears to be a simple solution sometimes isn’t. It’s useful to think of the battery as a zero impedance source with an annoying internal resistor between it and the terminal. That resistor’s value increases as the battery capacity is drained. If it were 50 ohms and the system needed 10 mA, the terminal voltage is down by half a volt, often enough to cause the MCU to crash. Add a big capacitor, as in the following diagram, and a short pulse load can draw on the charge stored in the cap.   One reader cited a TI white paper ( Coin Cells and Peak Current Draw ) where the authors conclude that this is a viable solution. They show a case where a capacitor must sustain a 30 mA load for 1 ms. An 87 uF capacitor will do the trick, though they recommend 100 uF since no one makes 87 uF devices. There are a couple of problems with this conclusion. First, the capacitor leaks. It’s always across the battery terminals, so is sucking juice, depleting the battery, even during long sleep intervals. How much leakage? It depends on a number of factors, including dielectric material. Let’s consider tantalums, which offer great capacitance versus cost figures. The following table shows the numbers for a 100 uF part. (For tantalums it’s usual to rate leakage in CV, where V is the rated, not the applied, value.)   The last column is the most telling. I started this series showing that MCU vendors who claim decades of potential operation off a CR2032 are completely off-base, and demonstrated that the longest life one could hope for is a decade (though few will ever achieve that). A CR2032 offers about 220 mAh of capacity, which means the average current draw over 10 years cannot exceed 2.5 uA. Just the capacitor’s leakage will suck the battery dry in a fraction of a decade. Who would have thought that a cap could leak more than Edward Snowden? How about a better part? The best low-leakage capacitors with the C values needed are MLCC. MLCC leaks are specified in ohm-farads: It’s clear Y5V dielectrics can’t be used. Select a more expensive X7R device. And, one must be careful which X7R is selected as some leak as badly as Y5Vs, though exhibit better temperature stability, which has always been the primary reason to use X7Rs. X7Rs are indeed very temperature stable, but not as a function of leakage! Here’s a typical graph of normalized leakage versus temperature:     A system that has to run over wide temperature extremes may leak two orders of magnitude more than shown in the previous table; that sweet AVX spec’d at 0.3 uA suddenly looks like a moderately low-value resistor. But even over room temperature, say 20 to 30 degrees, plan on twice the parasitic drain than specified. In the case of the AVX a quarter of the battery is lost to the capacitor. It gets worse. MLCC devices derate themselves. As the applied voltage increases, the effective capacitance decreases. Murata has a tool that helps model this, and here’s the result for 22 uF parts:     If space is precious you’re screwed. Apply 3 volts to a nice small 6 V 3216 device and only half the capacitance is available. The TI paper specifies a 100 uF part, but in this package you’d have to use 200 uF. Alternatively, one could use a higher-voltage (bigger and more expensive) device, or use a larger package as shown in the graph. Capacitors have tolerances, and though X7Rs typically are a good +/- 20%, one still has to figure that in:   Figure on an even bigger capacitor to deal with tolerance. The following graph shows the required capacitor, at 20 degrees C, for 10, 20 and 30 ms pulses with various loads, ignoring all of the complicated effects noted above. You’ll have to factor all of those parameters in as well, which, as we’ve seen, can more than double the required uF. The leakage numbers are based on that AVX component. Though the TI paper uses a capacitor to boost power for 1 ms, for Bluetooth and other protocols tens of ms are more likely.   So we’ve done the math, and have figured out what size capacitor to buy. Let’s ignore all of the unpleasantness and assume that the 100 uF part fits the bill, and that we’re using a low-leakage AVX part. They’re $14.50 each! Neither Digi-Key nor Mouser has them in stock, and quote a 25 week lead time. Digi-Key does have a 50 V version available today, but that will set you back $36.54. A complete Raspberry Pi with 700 MHz ARM processor and half a gig of RAM costs less than that capacitor. Maybe this is a government project where costs don’t matter. Using the graph above we pick off a 400 uF part for a 10 mA 20 ms load (remember, this is before all of the derating that must be done). The leakage will eat about half the battery capacity. And, the capacitor doesn’t exist; the biggest such part on the market is 220 uF. You can’t buy a bunch of smaller parts and parallel them, since the leakage will go up. What about a supercapacitor? These are astonishing devices that offer farad levels of capacity. Alas, the lowest-leakage supercap I can find is from Cap-xx, and they quote 2 uA at 23C, doubling at 70C. That’s impractical since even at room temperature it’ll eat just about the entire 2.5 uA current budget. To add another wrinkle, don’t forget that every MCU vendor requires one or more decoupling capacitors, even when running from a battery. Generally they want one of about 10 uF. Be sure to use a low-leakage part, and factor that into your battery capacity calculations. Summing up, in the use case I’ve described (ten years of system life from a coin cell) it’s generally impractical to get a pulse boost of Vdd from a capacitor across the battery. However, there are other ways to stretch battery life, which I’ll cover in coming weeks.

Am I crazy? My wife thinks so. She has been watching me discharging piles of coin cells over the last year, collecting millions of data points about their behavior. “Honey, exactly why are you spending all that money on batteries you’re just going to discharge?” It is pretty nutty, but the results are interesting, and dispel a lot of beliefs about what we can expect in long-lived, ultra-low-power, microcontroller-based products. Last week I wrote about the behavior of CR2032 coin cells in applications that have to run for a decade or so. My experiments quantified the batteries’ increasing internal resistance as they’re used. The net result is that, depending on the system’s current needs, the cell will appear dead long before it really is. That is, there will be plenty of capacity left, but none of it will be useable by the system. Several thoughtful readers wondered if adding a capacitor across the cell’s terminals could provide a short-term boost that could sustain a pulse load. It’s not hard to show mathematically that the answer is “yes.” But the math is irrelevant. In engineering we’re always faced by conflicting needs and what appears to be a simple solution sometimes isn’t. It’s useful to think of the battery as a zero impedance source with an annoying internal resistor between it and the terminal. That resistor’s value increases as the battery capacity is drained. If it were 50 ohms and the system needed 10 mA, the terminal voltage is down by half a volt, often enough to cause the MCU to crash. Add a big capacitor, as in the following diagram, and a short pulse load can draw on the charge stored in the cap.   One reader cited a TI white paper ( Coin Cells and Peak Current Draw ) where the authors conclude that this is a viable solution. They show a case where a capacitor must sustain a 30 mA load for 1 ms. An 87 uF capacitor will do the trick, though they recommend 100 uF since no one makes 87 uF devices. There are a couple of problems with this conclusion. First, the capacitor leaks. It’s always across the battery terminals, so is sucking juice, depleting the battery, even during long sleep intervals. How much leakage? It depends on a number of factors, including dielectric material. Let’s consider tantalums, which offer great capacitance versus cost figures. The following table shows the numbers for a 100 uF part. (For tantalums it’s usual to rate leakage in CV, where V is the rated, not the applied, value.)   The last column is the most telling. I started this series showing that MCU vendors who claim decades of potential operation off a CR2032 are completely off-base, and demonstrated that the longest life one could hope for is a decade (though few will ever achieve that). A CR2032 offers about 220 mAh of capacity, which means the average current draw over 10 years cannot exceed 2.5 uA. Just the capacitor’s leakage will suck the battery dry in a fraction of a decade. Who would have thought that a cap could leak more than Edward Snowden? How about a better part? The best low-leakage capacitors with the C values needed are MLCC. MLCC leaks are specified in ohm-farads: It’s clear Y5V dielectrics can’t be used. Select a more expensive X7R device. And, one must be careful which X7R is selected as some leak as badly as Y5Vs, though exhibit better temperature stability, which has always been the primary reason to use X7Rs. X7Rs are indeed very temperature stable, but not as a function of leakage! Here’s a typical graph of normalized leakage versus temperature:     A system that has to run over wide temperature extremes may leak two orders of magnitude more than shown in the previous table; that sweet AVX spec’d at 0.3 uA suddenly looks like a moderately low-value resistor. But even over room temperature, say 20 to 30 degrees, plan on twice the parasitic drain than specified. In the case of the AVX a quarter of the battery is lost to the capacitor. It gets worse. MLCC devices derate themselves. As the applied voltage increases, the effective capacitance decreases. Murata has a tool that helps model this, and here’s the result for 22 uF parts:     If space is precious you’re screwed. Apply 3 volts to a nice small 6 V 3216 device and only half the capacitance is available. The TI paper specifies a 100 uF part, but in this package you’d have to use 200 uF. Alternatively, one could use a higher-voltage (bigger and more expensive) device, or use a larger package as shown in the graph. Capacitors have tolerances, and though X7Rs typically are a good +/- 20%, one still has to figure that in:   Figure on an even bigger capacitor to deal with tolerance. The following graph shows the required capacitor, at 20 degrees C, for 10, 20 and 30 ms pulses with various loads, ignoring all of the complicated effects noted above. You’ll have to factor all of those parameters in as well, which, as we’ve seen, can more than double the required uF. The leakage numbers are based on that AVX component. Though the TI paper uses a capacitor to boost power for 1 ms, for Bluetooth and other protocols tens of ms are more likely.   So we’ve done the math, and have figured out what size capacitor to buy. Let’s ignore all of the unpleasantness and assume that the 100 uF part fits the bill, and that we’re using a low-leakage AVX part. They’re $14.50 each! Neither Digi-Key nor Mouser has them in stock, and quote a 25 week lead time. Digi-Key does have a 50 V version available today, but that will set you back $36.54. A complete Raspberry Pi with 700 MHz ARM processor and half a gig of RAM costs less than that capacitor. Maybe this is a government project where costs don’t matter. Using the graph above we pick off a 400 uF part for a 10 mA 20 ms load (remember, this is before all of the derating that must be done). The leakage will eat about half the battery capacity. And, the capacitor doesn’t exist; the biggest such part on the market is 220 uF. You can’t buy a bunch of smaller parts and parallel them, since the leakage will go up. What about a supercapacitor? These are astonishing devices that offer farad levels of capacity. Alas, the lowest-leakage supercap I can find is from Cap-xx, and they quote 2 uA at 23C, doubling at 70C. That’s impractical since even at room temperature it’ll eat just about the entire 2.5 uA current budget. To add another wrinkle, don’t forget that every MCU vendor requires one or more decoupling capacitors, even when running from a battery. Generally they want one of about 10 uF. Be sure to use a low-leakage part, and factor that into your battery capacity calculations. Summing up, in the use case I’ve described (ten years of system life from a coin cell) it’s generally impractical to get a pulse boost of Vdd from a capacitor across the battery. However, there are other ways to stretch battery life, which I’ll cover in coming weeks.

The answers to these ten questions will help you discover the very best in yourself. 1.What would make you proud of yourself? When you follow your heart and intuition,people won't always agree with you.When you find something that makes you happy,not everyone will be happy for you.When you show unwavering kindness to others,some people will question your motives.When you are honest to the core,some folks will attempt to use your honesty against you. Don't let any of these people stop you from doing these things.These people don't matter.In the end,what does matter is how you feel about yourself and the life you have led.You will ask yourself one question:"Am I proud of how I lived?"Make the answer:"Yes!" 2.How can you make a positive difference? Even when it seems like a hopeless effort,do the right thing.Always live firmly by the forces of love and truth.Keep injecting your goodness into the world,one small act at a time.It's these small acts of goodness stacked together that eventually change the world.You may never see the full result of your positive actions,but they will be accounted for and realized in time.If you do nothing,there will be no result-no positive change ever. 3.What are you trying to accomplish and why? Know the answer to this simple question and remind yourself of it every single day.You must identify,without any doubt,the specific reason you do the work you do.Success can only occur when there is target and a reason to hit it. When you have a reason to do something,you have a legitimate purpose behind your efforts.When you connect this reason to a desired result,you're able to summon the discipline and persistence necessary to get the job done.Give yourself a good reason and you will find a way to succeed. 4.What are the roadblocks standing in your way? A roadblock is only a roadblock if you do not know about it.If you know about it,it is just a challenge.Look around and evaluate the challenges you face;within them lie the opportunities to make lasting progress.You are in the best position to make the most of these opportunities,because you know exactly where you are,where you want to go,and what resources you have at your disposal. Remember that the roughest roads often lead to the top,and the best way to get over a roadblock is to go through it.Thus,you must run toward your challenges with all your might,because the easiest way through them is to trample them beneath your feet.You have what it takes right now.You know what you must do and you know why.Step confidently into your challenges until you reach road on the other side. 5.What is the next step? Remember,you will never make a bigger mistake than sitting back and doing nothing simply because you can only do a little.So go head and start small.Take a small step,and if you can not take a small step,take a tiny one.Do what you can with the resources you have right now.Get yourself moving in a positive,productive direction. The best thing about big success is that it comes one step at a time.A flash of success,no matter how small,creates the momemtum necessary to create even more success.Every positive step forward puts you in position to take the next one. 6.What are your faults and flaws? You will never be flawless.You will never be faultless.Acknowledge your flaws and faults and accept them.Let the difference between your flaws and the flaws of others be that you have accepted their existence and moved past them,while others are hopelessly trying to hide them.Let the difference between your faults and the faults of others be that you have addressed  them and learned from them,while others are still living in denial. Do not fall victim to fabricated illusions.Do not hide from reality.Face your deficiencies and use them to bask in the glory of your personal growth. 7.What issues do you need to resolve with yourself? When you feel lonely you look around for someone to fill the void in your life.You assume that your loneliness stem exclusively from being alone.But once you find company,it doesn't take long before you realize that there is still a void in your life.You still feel lonely and unfulfilled,so you blame it on your company and you move on to someone else ... and then someone else.This cycle perpetuates for months,or even years,until you are eventually ready to face the truth. The truth is,a partner,or even just a friend,can add lots of beauty to your life,but they can not fill a void that exists within you.You alone are responsible for you own fulfillment.If you feel desperately lonely when you are alone,it means you're in bad company.It means you need to work on your relationship with yourself first.To believe otherwise is to delude your mind and perpetuate your loneliness as you hop from one failed relationship to the next. 8.How are you burdening yourself? If you feel like your back is breaking from the weight your mind is carrying, perhaps it is time to lighten the load you carry.There are many burdens you can easily let go of if you are willing. Start by leaving your worries behind you;worries only fill your mind with negativity.Instead take constructive action - get involved in something worthwhile that takes your mind off of things.Grudges and resentments simply suck energy and time away from yu without any positive return.Once you have gotten this far,it's time to stop pretending like you know everything.And before you wrap things up,let go of your impatience.Two of the most vital virtues of your personal growth will be your patience to wait for the right moment and your courage to make the best of it. As you can see,dropping burdensome negativity from your life is fairly easy once you realize how much of it you're carrying around with you.Do yourself a favor today and lighten your load. 9.How have you celebrated your progress lately? Focus on the progress you have made, on the next positive step,on the silver lining between where you once were,where you are now,and where you are headed.Do not think of yesterday's failures,but of the success that is possible today. Be proud of yourself.The fact that you are trying is immensely impressive.You have conquered complacency.You are crushing your fears with every new effort you put forth.You aren't where you want to be yet ,but you're making progress.Step by step will get you there.Even if you feel like you are running in place,you are not.No effort that you make to attain something worthwhile is ever lost.It doesn't matter how slow you go as long as you don't give up. 10.What do you love about your life? Life is a series of highs and lows.There will be times when bad things happen.When these times strike,it is important to keep things in perspective.How you respond to life's inevitable difficulties defines the strength and growth of your character,as well as the quality of your life.The idea that you are a victim of any particular circumstance is simply inaccurate. The fleeting ups and downs that occur on a daily basis are tiny threads in the overall fabric of your life.Each one adds to your personal growth.The quality of your life is ultimately your choice.You can choose to be immobilized by the gravity of your disappointments,or you can choose to rise from suffering and treasure the most precious gift you have - life itself.