Differentiators and OP-Amps

Differentiators and Short Pulses

I have been working with Rob on this forum thread.

@Robert93820 has kindly pointed me in the direction of Differentiator Circuits.

I want to try building one and this picture is promising the right thing : Short Blips on the rising edge of a clock.

image

But I’d love some clarity on the difference between these two chips.



In truth it seems like I only need one OP amp.
Is it possible to make an OP amp entirely from transistors?

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Hey @Pixmusix
The short answer is the LM324 is better in every way and you may as well use it. four opamps for about half the price of the 741!

Opamps are analog devices and have numerous important specifications like bandwidth, input offset voltage, gain etc. You should compare their datasheets for a more exact idea, but in any case the 324 is just better value.

The 741 is a historical specimen that kind of shouldn’t be used for anything other than the most basic projects - it’s super-good-enough for maker projects, but there’s usually a better alternative. That said you can still get a lot done with them; I had to simulate the motion of a mass-spring damper system using several of these as adders and integrators for an Opamps course at university.


Historical aside

I love how deep down the rabbit hole you’re going :sweat_smile: This differentiator circuit (and other opamp circuits like adders, integrators) are the foundations of how analog electronic computers were made to solve complex problems like simulating dynamical systems. All you need to simulate the way a projectile flies through the air, a swinging pendulum, or how a car’s suspension moves, is a few integrators and adders.

Originally computations were done with mechanical versions of these components, then the mechanical versions got miniaturised into exactly the circuits you’re looking at now.

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Noted. Might be a fun chip to come back to, but I’ll start with the LM324.

I’ve learned since posting this a lot about passive vs active differentiators.
I’m going to start with some passive solutions and then return here for an active one if required.



This is wild! I had a read of the OP amp Wikipedia article and I think it’s going to be one of those things I need to come back to after my theory has improved.

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Hi Pixelmusix
Looks like you are on a big learning expedition here.
I will be posting your modified circuit drawing on your other thread shortly with a passive differentiator.
I don’t know if you noticed but the particular OP amp circuit you have been looking at needs a split (that is pos and neg) power supply. That is a bit of a turn off as most projects these days have a pos supply only. Can be done but sometimes a bit of a pain.
Do yourself a favour on this venture and get a few basics re at least DC theory under your belt first. Makes things a bit easier when you get into it a bit deeper.
Cheers Bob

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For hobbyist like me without a background in engineering, is there a particular book or resource that is recommended? How did all the hobbyists on this site learn to speak the jargon and read these insane online circuit diagrams?

I’m still blown away you’re doing that for me! So grateful.

Hi

That is a hell of a question. There are literally libraries full of this stuff of varying degrees of complexity. Some of them I think are written by Maths gurus and are full of formulae you would probably never use.
I think in general the Cookbook style are more plain language. I have a TTL Cookbook also the OP Amp Cookbook would be OK the one I have is Understanding Operational Amplifiers. haven’t read any of them but maybe the “For Dummies” series might be OK. I note that some want to start half way or more up the tree but I don’t think that is wise as this subject can be very confusing later on. I know on one course I did the class actually halved with drop outs when we got into Decibels. That is half the class could not comprehend just what this little term is all about. I must admit though when that course started we were told in no uncertain terms we were going to do a 4 year course in 2 years and if we didn’t think we could do this the time to leave was now. Blunt and to the point. We finished up with a class size of about 30%.
Cheers Bob

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If you really want to go the book route I would recommend The Art of Electronics by Horowitz and Hill. It’s a massive bible of a thing but it covers at least the first 3 years of an Electrical Engineering bachelors degree starting from the very basics with less assumed knowledge than you already have. It is also incredibly practical explaining things in terms of applications, not just death by formulae. I only discovered it toward the end of my degree and wish lecturers had realised there only needed to be 1 textbook recommended in first year.

For the non-book route I’d recommend to keep doing what you’re doing, find projects that are interesting and a bit daunting and see what you learn when you’re investigating them.
Following along with someone elses build on Youtube is a great way to pick up jargon and obscure bits and pieces as well.

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Sounds Perfect.

I’m in too deep now I don’t think I could get out now if I needed to.

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Hi Pixmusix
Just posted your modified circuit on the other thread.
Cheers Bob

Hi Pixmusix et al,

This is also a useful book, noting that I would read this one AFTER the previously mentioned tome, as it seems to go in assuming some depth of prior knowledge

Practical Electronics for Inventors, 4th Edition by Paul Scherz & Simon Monk (4th edition)
ISBN 978-1-25-958754-2

FYI: The Art Of Electronics, 3rd Edition is
ISBN 978-0-521-80926-9 Hardback

Murray

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Agree with Murray - “Practical Electronics for Inventors” 4th Edition is a great detailed reference.
I use this book as my main reference when I teach electronics to Electricians, and I use the LM324 for a couple of practical exercises.
The advantage of the 324 over the 741 is that it runs on a single power supply, but you need a biasing network for some applications such as audio amps.
Also recommend the LM358 as an alternative.

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or LM258, much the same thing
Cheers Bob