Practical Electronics for Inventors, 3rd

[uwezi]

Page 448, middle of the paragraph about monostable multivibrators it states "the capacitor suddenly behaves as a short circuit (a capacitor likes to pass current when the voltage across it changes suddenly)". Is this correct? A short for *any* kind of current, including DC? Or just high frequency current?

It is not a nice wording, but essentially it is correct. If you connect a discharged capacitor to a DC voltage source you will have an inrush of current which is only limited by the ESR of the capacitor, your wiring and the capability of your voltage source.

There are other ways to interpret or describe this phenomenon, one would be to see the voltage step as composed of an infinite number of frequency components (Fourier) or just as a step (Laplace). In the Fourier-view you will see that the impedance of the capacitor for infinitely high frequencies becomes infinitely small, allowing an infinite current to pass (for an infinitely short amount of time). You get rid of the infinities if you stop to neglect the series resistances, but this does not make the math simpler.

However, the current is not actually passing through the capacitor! The capacitor is charged by collecting the inrushing charges on its electrodes, but it looks as if the current would actually pass through the capacitor.

This behavior is also utilized in differentiator circuits: the current through the capacitor is proportional to the derivative of the applied voltage. The derivative of an ideal step is infinite. However, real steps are rarely infinitely sharp, and hence the derivative in all our practical circuits will be finite.

[TomC]

Page 448, middle of the paragraph about monostable multivibrators it states "the capacitor suddenly behaves as a short circuit (a capacitor likes to pass current when the voltage across it changes suddenly)". Is this correct? A short for *any* kind of current, including DC? Or just high frequency current?

If they really mean it acts like a short, I'm surprised that the crux of their explanation is predicated upon an undisclosed (in the book, to this point) property of capacitors. And that this property isn't explained beyond the above phrase.

Hi Legion,

I just read that excerpt, I think that, in the context of a sudden change to ground, saying that the capacitor will act as a short is a fair description of the effect caused by the capacitor charging. Of course, you will only see ground on the other end of the capacitor momentarily, and as the capacitor charges you'll begin to see a voltage drop across it. But at the time you apply ground to one end of the capacitor, you are going to see ground on the other end for an instant, just as if you had placed a short across the capacitor.

While reading the text for the monostable multivibrators I ran into the following sentence that appears to have a small mistake:

 "It can be thrown into its unstable state by applying an external signal, but it will automatically return to its unstable state afterward."

I think it should be corrected as suggested.

[TomC]

I've been looking at Appendix D from the 2nd edition and I think I realize now why it wasn't included in the 3rd edition. There are too many mistakes and omissions. I never looked at it in detail before and didn't suspect that at least over half of the specs contained errors, even the list of standard resistor values is missing half of the E24 values. I'm trying to fix it, but I'm beginning to think that it may be easier to rewrite it from scratch.

Just wanted to let everyone know that the specs in that appendix are at best unreliable and at worst dangerous. 

For example, the 2N5210 is shown to have a max collector current of 50A, the correct value is 50mA. Many more wrong specs like that in that section. So I suggest that it is best to suspect everything and look at a manufacturer's datasheet instead.

[Astroplio]

Hello guys, sorry for the delay I was busy!

@ablacon64
I attach below the aforementioned table with the recommended components from the 2nd edition of the book.

catch you later!

[Rigby]

Not related to the book, I guess, but I think someone should come up with a digikey cart link that contains all of these parts in the quantities specified.  Perhaps combine the 2nd and 3rd edition parts recommendations and just put together a cart in digikey and share a link to it.

maybe I can tackle that this weekend.

[rivest]

TomC, I took the initiative to upload the errata to google drive. I believe it will be a much faster download for most:

http://docs.google.com/file/d/0Bxp03EhzdniIeElNT21EcDVzSTg

[ablacon64]

@ablacon64
I attach below the aforementioned table with the recommended components from the 2nd edition of the book.

Thank you! Another user has already sent me, we were afraid to brake forum rules posting them here. I see no problem since I've already bought the 3rd edition.

BTW, Rigby's idea is very good, maybe we could come up with an essential parts list for all to have on the lab (I'm always missing something...).

[Legion]

Bottom of page 687 and top of 688 describes a 555's astable mode. Perhaps I'm not understanding their explanation but I think they've made an error here:
"With Qbar high, the discharge transistor is turned on, which allows the capacitor to charge toward V_cc through R₁ and R₂." However, a few sentences later they say "At this point, the discharge transistor turns on and shorts pin 7 to ground, discharging the capacitor through R₂."

I think the first sentence may be in error as it would make more sense if the transistor were off for the capacitor to charge.

[TomC]

Bottom of page 687 and top of 688 describes a 555's astable mode. Perhaps I'm not understanding their explanation but I think they've made an error here:
"With Qbar high, the discharge transistor is turned on, which allows the capacitor to charge toward V_cc through R₁ and R₂." However, a few sentences later they say "At this point, the discharge transistor turns on and shorts pin 7 to ground, discharging the capacitor through R₂."

I think the first sentence may be in error as it would make more sense if the transistor were off for the capacitor to charge.

You are right Legion. The transistor needs to be off for the capacitor to charge. Some rewording on one or both pages is needed to fix this mistake.

Thanks a lot for reporting this error!

[TomC]

The partial paragraph below is how I think the text on pages 687 and 688 could be corrected. The strikethroughs on the Qs are meant to be overlines, I don't know how to render overlines with this forum's text editor.

      "With Q high, the discharge transistor turns on and shorts pin 7 to ground, discharging
      the capacitor through R₂. When the capacitor's voltage drops below 1/3V_CC, comparator 2's
      output jumps to a high level, setting the flip-flop and making Q low and the output high.
      With Q low, the transistor turns on, allowing the capacitor to start charging toward V_CC
      through R₁ and R₂. When the capacitor voltage exceeds 1/3V_CC, comparator 2 goes low,
      which has no effect on the SR flip-flop. However, when the capacitor voltage exceeds
      2/3V_CC, comparator 1 goes high, resetting the flip-flop and forcing Q high and the output
      low. At this point, the discharge transistor turns on again and shorts pin 7 to ground,
      discharging the capacitor through R2. The cycle repeats over and over again. The net
      result is a squarewave output pattern whose voltage level is approximately V_CC - 1.5V and
      whose on/off periods are determined by the C, R₁, and R₂."

[Legion]

The partial paragraph below is how I think the text on pages 687 and 688 could be corrected. The strikethroughs on the Qs are meant to be overlines, I don't know how to render overlines with this forum's text editor.

      "With Q high, the discharge transistor turns on and shorts pin 7 to ground, discharging
      the capacitor through R₂. When the capacitor's voltage drops below 1/3V_CC, comparator 2's
      output jumps to a high level, setting the flip-flop and making Q low and the output high.
      With Q low, the transistor turns on, allowing the capacitor to start charging toward V_CC
      through R₁ and R₂. When the capacitor voltage exceeds 1/3V_CC, comparator 2 goes low,
      which has no effect on the SR flip-flop. However, when the capacitor voltage exceeds
      2/3V_CC, comparator 1 goes high, resetting the flip-flop and forcing Q high and the output
      low. At this point, the discharge transistor turns on again and shorts pin 7 to ground,
      discharging the capacitor through R2. The cycle repeats over and over again. The net
      result is a squarewave output pattern whose voltage level is approximately V_CC - 1.5V and
      whose on/off periods are determined by the C, R₁, and R₂."

There's still a contradiction in there. The first sentence says "With Qbar high, the discharge transistor turns on..." A couple lines below it says "With Qbar low the transistor turns on..."

My understanding is that whenever Qbar is high the transistor is on and the cap discharges. Whenever Qbar is low the transistor is off and the cap charges.

[TomC]

There's still a contradiction in there. The first sentence says "With Qbar high, the discharge transistor turns on..." A couple lines below it says "With Qbar low the transistor turns on..."

My understanding is that whenever Qbar is high the transistor is on and the cap discharges. Whenever Qbar is low the transistor is off and the cap charges.

I'm glad I posted that before creating new pages!

Of course you are right, again!

Very easy to slip up even when you know what you want to say. I think the edit below may be OK:


      "With Q high, the discharge transistor turns on and shorts pin 7 to ground, discharging
      the capacitor through R₂. When the capacitor's voltage drops below 1/3V_CC, comparator 2's
      output jumps to a high level, setting the flip-flop and making Q low and the output high.
      With Q low, the transistor turns off, allowing the capacitor to start charging toward V_CC
      through R₁ and R₂. When the capacitor voltage exceeds 1/3V_CC, comparator 2 goes low,
      which has no effect on the SR flip-flop. However, when the capacitor voltage exceeds
      2/3V_CC, comparator 1 goes high, resetting the flip-flop and forcing Q high and the output
      low. At this point, the discharge transistor turns on again and shorts pin 7 to ground,
      discharging the capacitor through R2. The cycle repeats over and over again. The net
      result is a squarewave output pattern whose voltage level is approximately V_CC - 1.5V and
      whose on/off periods are determined by the C, R₁, and R₂."

[Legion]

I'm glad I posted that before creating new pages!

Of course you are right, again!

Very easy to slip up even when you know what you want to say. I think the edit below may be OK:


      "With Q high, the discharge transistor turns on and shorts pin 7 to ground, discharging
      the capacitor through R₂. When the capacitor's voltage drops below 1/3V_CC, comparator 2's
      output jumps to a high level, setting the flip-flop and making Q low and the output high.
      With Q low, the transistor turns off, allowing the capacitor to start charging toward V_CC
      through R₁ and R₂. When the capacitor voltage exceeds 1/3V_CC, comparator 2 goes low,
      which has no effect on the SR flip-flop. However, when the capacitor voltage exceeds
      2/3V_CC, comparator 1 goes high, resetting the flip-flop and forcing Q high and the output
      low. At this point, the discharge transistor turns on again and shorts pin 7 to ground,
      discharging the capacitor through R2. The cycle repeats over and over again. The net
      result is a squarewave output pattern whose voltage level is approximately V_CC - 1.5V and
      whose on/off periods are determined by the C, R₁, and R₂."

Reads right to me!

[TomC]

Just uploaded an updated version of the unofficial errata!

https://onedrive.live.com/redir?resid=967A90CA47FD025B!172&authkey=!ACEbpvA4f9gUlxc&ithint=file%2c.pdf

[Rigby]

+1 for OneDrive.

+100 for impressing me.   You've spent a hell of a lot of time on this, wholly for benefiting others.  Thank you.

[Legion]

At the bottom of page 772, figure 12.72 they show an SR flip-flop with NAND enable gates so a clock signal can be fed in. Why NAND? It seems like AND gates would make much more sense.

[TomC]

At the bottom of page 772, figure 12.72 they show an SR flip-flop with NAND enable gates so a clock signal can be fed in. Why NAND? It seems like AND gates would make much more sense.

Since the SR flip-flop is built with cross-NANDs, you need a low at the Q input to set it, or a low at the Qbar input to reset it. If the enable gates were built with ANDs, you would need to invert their output before the signal was fed into the SR flip-flop inputs. By using NAND gates you eliminate the need for the extra inverters resulting in a simpler circuit.

[Witention]

I've had previous versions of this book and it just keeps getting better, and bigger. It does a great job of explaining electronic devices and concepts such that even a novice can understand it, while at the same time providing sufficient details to make it a practical reference for experimentation and development. No electronics experimenter should be without this outstanding book.

[E-lectr0de125]

Just uploaded an updated version of the unofficial errata!

https://onedrive.live.com/redir?resid=967A90CA47FD025B!172&authkey=!ACEbpvA4f9gUlxc&ithint=file%2c.pdf

Dear TomC,

    I want to say first thank you for your work. I would like to submit a candidate error for consideration. On page 18, example 1 seems to have errors in the calculations. For example, in part b, they list the voltage from point B to point C as +9 V. However, this seems to be inconsistent with the way he obtains voltage measurements for the other points (this error also extends into parts c and d). The value should be -9 V however as by how I see it, the calculation is putting the positive lead of the voltameter on B and the negative lead on C (that's how +3V was gotten for the voltage between A and C in part b as far as I can tell).

[TomC]

Dear TomC,

    I want to say first thank you for your work. I would like to submit a candidate error for consideration. On page 18, example 1 seems to have errors in the calculations. For example, in part b, they list the voltage from point B to point C as +9 V. However, this seems to be inconsistent with the way he obtains voltage measurements for the other points (this error also extends into parts c and d). The value should be -9 V however as by how I see it, the calculation is putting the positive lead of the voltameter on B and the negative lead on C (that's how +3V was gotten for the voltage between A and C in part b as far as I can tell).

Hi E-lectr0de125,
Thanks a lot for your input regarding example 1 on page 18.

If I understand correctly, you are trying to figure out the reference point the author expects you to use when determining the voltage between two points, or in other words, how to connect the voltmeter leads. As far as I can tell, this is not stated anywhere in this case, so there are two possible answers for each question, one would be a positive voltage, and the other an identical negative voltage. However, in the cases where one of the points is connected to ground, I think it's safe to assume that this is the reference point where you would connect the negative lead. The answers given contain at least one of the possible correct values depending on how you connect the leads, so I'm not sure if a correction is needed there.

However, there is obviously something confusing about this example or you wouldn't have brought it up. So maybe the problem should be stated differently or should clearly state which point is the reference. I'll wait and see if there is more feedback on this issue before adding it to the errata.

[nixfu]

Just wanted to chime in and say that this book is excellent.    Its a great reader, and a very good reference.

It is quite possibly the best book on electronics available today, and is right up there with Horowitz's AOE which I have also read.

Thanks for the fantastic book recommendation.

[NinjaBristle]

I have a question about the differential amplifier on page 446.  In the top paragraph it says that a larger current will flow in the right transistor if V1 is larger than V2.  Is that correct? I thought that essentially the right transistor would be cut off if V1>V2.

Thanks

[TomC]

I have a question about the differential amplifier on page 446.  In the top paragraph it says that a larger current will flow in the right transistor if V1 is larger than V2.  Is that correct? I thought that essentially the right transistor would be cut off if V1>V2.

Thanks

Hi NinjaBristle,

Thanks for pointing this out, as far as I can tell this is incorrect. I think the error can be fixed by changing the sentence: "Now, assume the signals applied to the inputs are different, say V1 is larger than V2." to the following: Now, assume the signals applied to the inputs are different, say V2 is larger than V1.

I'll add this to the next revision of the errata.

[edy]

Awesome book! I am now working my way through the 3rd edition, after making my way a bit through an older what I assumed to be the 1st edition down at my local library (which only had Paul Scherz as the author?).... It was dated copyright 2000. Not sure when 2nd edition came out, but the 3rd edition looks easier to understand. I was struggling with the RC/RL/RLC circuits and the phasor diagrams, trying to get a grip on intuitively what is going on and not just relying on the math calculations! I hope the new book helps in this regard... can't wait to work through it....

[cdwilson]

@TomC this is an AMAZING contribution, thanks!  I just found this thread after posting this errata question on EESE http://electronics.stackexchange.com/questions/123891/bipolar-transistor-switch-base-current-calculation-example-from-pefi-seems-wrong

I don't see this issue in the last errata pdf you published.  Can you have a look at the question and see if there is really an error in the text, or if I'm just misunderstanding something about how BJTs work?