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Compression by the resistor

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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It's Robyn, well actually Robin, but people have been spelling it with a Y here so I went on with :) I'm actually from south of France but I've been in Melbourne for 3 and a half years now.
Wow! Your English is excellent! I thought the French resented having to speak English.
I really like the fact that this page goes through the whole process of troubleshooting the weaknesses of a simple discrete design. I've always been looking for this kind of approach as I believe it is the best way to learn.
Yes, it seems like a natural way to present the lesson. Start with the basic idea, then give it the full engineering treatment.
This particular case is a bit to extreme though as I am not sure that any of my PNP's are functional :rolleyes:.
Right. Personally I would throw them all out and buy new ones. They aren't that expensive.
I am not 100% sure that this is what happens. It seems like it but I am still fragile with my handling of metering tools so I would double check this finding (if you have a couple of PNP's to spare!). I enjoy this way of learning though, trial / error / observation / conclusion. It helps my artist brain make sense of the equations by being able to "feel" what happens in the circuit. I was watching a documentary about Robert Moog recently and he mentioned this intuitive approach. I guess I got a glimpse of what he meant :)
Sure. I like designing with discrete components. It's the way I learned originally, and even now, very few designs, perhaps none, can get away from discretes completely.
Regarding intuitive understanding of voltage and current, I'd like to get your feedback on an idea I posted here a while ago. It's an explanation for voltage, current and resistance that equates them to distance, tension, and stretchiness. A resistor is modelled as a tension spring. The introductory post is at https://www.electronicspoint.com/newbie-questions-t248766.html#post1470672. I would appreciate your opinion.
(re my sister) Well if she is ever around Gertrude St. in Fitzroy she should come to Southpaw. I am barista there, mainly on weekends and I would be happy to shout her a coffee!
Cool! She's a barista too, among other things, but she's not working as one now. I'll let her know :)
I just watched this video:
. Also going to check the two books I bought (Electronics for dummies & Electronics demystified) for infos about our 5 legged friends (seems like they come more in 10 legged twins these days!).
Edit: Another great op amp video: http://www.youtube.com/watch?feature=endscreen&NR=1&v=OMJ9WGrRf6A
Edit 2: Oh my god this all makes so much sense!
Edit 3: :D
Thanks for the links. I'll check out the videos when I'm at home and have proper bandwidth.
Thank you again very much, would be great to meet you in person if you pass by Melbourne again.
Cool! It's a pleasure to be able to help someone who is so intelligent and resourceful. Compared to many of the folks we get here, you're a breath of fresh air my friend.
 

Robyn

Apr 17, 2013
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Regarding intuitive understanding of voltage and current, I'd like to get your feedback on an idea I posted here a while ago.

It's great, it helps making sense of the counter intuitive nature of voltage dividers, and the change in resistance of capacitors as they charge up. It would be awesome to build a working physical model of this for kids!

BTW, thanks to the modo for merging the two threads.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Thanks for the feedback :) To be picky though (which I am), the capacitor's resistance doesn't change as it charges up. The voltage across it increases, but it's not meaningful to say that its resistance changes, because resistance only relates to something with the quality of a spring, where the tension varies directly with the distance between the ends (or vice versa).
I was thinking of building a virtual simulation, not a physical one, because then anyone could use it. I would like to make this model available as a tutorial, with probably a Java-based implementation of the model.
Good luck and please feel free to ask any other questions in the forums or by PM.
Kris
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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I see nothing wrong with playing with discrete circuitry. After all they're the building blocks of ICs.

In case you want to try driving your PC Line Input with your sawtooth osc. I've included a JFET Buffer and a Level Control (P1).

Chris
 

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Robyn

Apr 17, 2013
34
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Hey Chris,

Thanks a lot for redesigning this circuit. I am just about to breadboard it now. Sorry it took so long to answer, I had to work over the weekend.

I had a look at your changes to try and understand your design choices. I think I understand part of it but not all.

1. R1 and R2 form a voltage divider which ratio is bigger than the one on the original circuit (0.66666... instead of 0.1). Is this because your value for U1 drops from 12V to 4.5V so the voltage division can be smaller? I wanted to calculate the base / emitter voltage because it seems like this is what would define the value of the voltage divider but I don't understand how to calculate the voltage drop at P1. V = R * I but what is I? Is it the amps fed by my voltage source?

2. I have tried to understand the role of C1. In this configuration it seems to be called a "bypass capacitor" which purpose is to avoid negative feedback. How do you pick C1's value?

3. Does C2 get rid of DC in order for the low peak of the wave to go no higher than 0V? Also wondering how you choose its value.

4. I don't understand the "team" R3, R5, C3. I guess they form a network together which serves a purpose, what is it?

I guess all these questions come from my poor circuit analysis skills. I can't put my head around the importance of current vs. voltage yet. I know what each of them is (current = "pressure of the flow", voltage = "amount of electricity flowing") but not what their respective roles are. Maybe that's something Kris (with a K) can shine light on with his fancy "springs metaphor"...

Again thank you for your help and patience. Going to rush on my breadboard while waiting for your answer!

Edit: Did a simulation before building so I can see the electrons going around. It tells me the JFET is reverse biased :(

I set a hFE of 250 for the transistors and a cutoff voltage of 5V for the JFET. Here is a Java simulation: http://www.falstad.com/circuit/#$+1...625E-5+0+-1 o+1+64+6+35+5.0+9.765625E-5+1+-1
 
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