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According to Pete


As some of you undoubtedly noticed, we didn't post the September edition of "According to Pete" yesterday because of the Labor Day holiday. However, you'll be happy to know we didn't forget - so here it is, "According to Pete."

In this episode, Pete heads back to SparkFun HQ to explore the wonderful world of OpAmps. It's a thrill-a-minute as Pete talks about voltage gain, using an OpAmp as a comparator, and so much more! Check it out - we hope you enjoy it!


Comments 25 comments

  • I have been reading some audio design books.
    So far the best author seems to be Douglas Self
    Ex: http://www.amazon.com/Small-Signal-Audio-Design-Douglas/dp/0240521773/ref=ntt_at_ep_dpt_1
    The LMV358 at first glance seems to be a good amp for Audio, 1mhz unity gain, …
    Look at the NE5532. Far better slew rate, and awesome little (cheap) opamp. The only trick with this amp is to push a little more current into the input. (just divide the resistors by 10-20). I have been making audio projects with the 5532 and am very pleased.
    Sparkfun should look at this amp (and the self books). Improved my designs x10.

  • I didn’t know Pete made it to Hollywood!
    http://tiny.cc/qwvsg

  • I really do wish that you could do these more often

  • These videos are phenomenal. OpAmps are one of the things I struggled with in school. I got (and forgot) all the formulas, but never actually learned how or why they work. It’s nice to see a simple yet surprisingly complete intro to these devices.
    My only issue is that I can’t find a list of past “According to Pete” videos. I missed a couple and wanted to go back to catch up, but I don’t see them (I’d rather not sort through the whole SparkFun YouTube channel!). What about making another Tutorials page and listing all these videos in one place?
    Thanks for doing this video series, Pete!

    • Sparkfun is opening a learning site at learn.sparkfun.com. I have a feeling his videos will be posted there.

      • I fear that. Personally, I think I ought to be tarred and feathered for what I’m doing. But thanks all for the good words.

        • I think videos like these are great. Sure there may be inaccuracies and uncapped felt and such but ask yourself this: Are teachers in classrooms scrutinized by people from all of the globe? Teach to an audience ranging from those just learning about capacitors and resistors to those who are seasoned veterans of the silicone world?
          Classroom teachers have the luxury of not having their mistakes captured and broadcast for people to point out. I have seen many teachers make errors in class and sometimes students spot them and sometimes they don’t. Just keep doing your best, it is an excellent resource for new people. Sometimes, when we are doing something we love, it feels so little like work that we wonder how we are getting away with it. Try to be as technically correct as possible and don’t sweat the rest. Mistakes will be made. Unless you want to spend a whole day doing multiple takes, reviewing the footage etc, then I don’t know if you want to invest that much time.
          Cheers!

        • You mean you’re not worried about having little red boxes glued all over you? (SparkFun’s version of tarred and feathered.)
          Also I am surprised that you did not talk about adding a cap across your rails, as when you need to do that.

  • OMG I am so happy. Have been refreshing all day! :-)

  • A while back I needed an equal positive and negative DC supply. So I used an op amp, some transistors in a half bridge, and various components to buffer the voltages and limit currents to make a virtual ground system. Basically you put a wall wart or some other filtered dc on it and it will put a ground in the exact center of the potential. Really nice for breadboarding as it plugs across one end of the breadboard to provide the 3 voltages.
    Thanks for this tutorial. I really enjoyed the information.

  • You videos are awesome. I always walk away with at least one new bit of information. This week I learned about the virtual ground.

  • Thank you for this! Every time you put out a video my skills increase ten fold. Keep this up Pete (and Sparkfun!)

  • Inverting mode has a gain of -R2/R1. Hence the name inverting. Other than that, good job Pete.

  • What I remember about op-amps from school is: Always connect the output to the input. Thanks for reminding me why you do that, and for showing an application where you don’t do that.

  • Pete,
    Great presentation but if I may may a couple of suggestions;
    1) Try not to speak quite so fast - you are sometimes hard to follow - especially if a person is new to the topic. You need to give your audience a moment to digest what you have just said.
    2) To avoid your pen drying out and thus being hard to read when you next use it, remember to put the cap on every time after using it.
    I hope this helps you.

  • Pete is not just awesome but a great guy. It’s not just clear video but big topic, good !

  • Yay, Op Amps! My favorite! Just grab a fistful and you have amp, filter, oscillator, comparator, etc. depending upon your passives. You can do so much once you learn what to do with the assumptions! Grab a fistful.
    As an alternative to the big, fat input cap, try an Op Amp follower and a smaller cap, to “amplify” the capacitance. If you have a spare Op Amp on-die. Remember, a 1458 has the same number of pins as a 741. :-)

  • what no 1080p I liked watching this on the flatscreen.

  • To be more precise, a buffer has a voltage gain of 1, not of zero ;-).
    And the + and - inputs are not coupled internally. The virtual ground is created by the feedback. If you remove the feedback, the virtual ground is gone.
    Also the gain bandwidth product is something to keep in mind during designing. If you want to amplify 100µV with an opamp to 10V (wouldn’t advise doing so without using a low noise opamp) it requires an amplification of 100,000x . If your signal has a bandwidth of 1000Hz,you need a pretty decent opamp to achieve it!

    • I heard myself say “zero gain” and immediately thought “you idiot”. Correct, gain = 1. On the inputs being held close together internally… I got that from a lesson way back, and it sorta slipped out before I checked myself. Obviously that can’t be true in the case of a comparator, but I’d want to do a little more homework before I totally back off of it. Not calling you wrong, but it is the nature of an engineer to do the research themselves rather than trust what someone else says. For now, the point is yours and the ball is in my court.

      • I heard myself say “zero gain” and immediately thought “you >idiot”. Correct, gain = 1.
        You’ve probably meant 0 dB.

      • The virtual ground is created because in a circuit where the opamp is used in a feedback setup, the opamp “tries” to keep the potentials at the + and - input equal. (That is the simple explanation). So if the + input is grounded (via a resistor) automatically the other one will get a similar potential (ground).
        Since the input impedance of the inputs is high, you can say that there will be no current flow into the opamp. So if a resistor is used between the + input and ground, the potential at both sides of the resistors will be equal.
        Opamps are interesting devices… It is very difficult to put it “all” in 20 mins of video… (i.e. what happens when you drive the + and - with the same voltage/signal…)
        But I think the basics have been covered in it.
        (A reference for basic designs: http://www.physics.unlv.edu/~bill/PHYS483/op-amps.pdf )

  • Oh, and nice name Pete!

  • Pete is awesome. Big topic, clear video!

  • For further reading on Op Amps, you may also want to check out Op Amp Applications Handbook by Walter Jung ISBN 13:978-0-7506-7844-5.
    As engineering is the science of making tradeoffs, it is difficult to make any Op Amp selection that will work for everyone’s needs. One needs to know the important requirements for the design before selecting the Op Amp that will best fulfill the requirements.
    Cudos to Pete for taking a stab at an intro to Op Amps.


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