4 ms·

At university one of the mandatory courses was Computer Organisation, which teaches how computers are built electronically. Two weeks of that course covered DRA

by tinco 5y ago

At university one of the mandatory courses was Computer Organisation, which teaches how computers are built electronically. Two weeks of that course covered DRAM timings. Recently (almost 15 years later) I was trying to design a simple automation system for my home's ventilation system, and for it I needed to pull my logic signal up to 10v using a FET. I had absolutely no idea how to do that. It's absolutely crazy that at some point I was able to (crudely) design a computer logically to the level of detail of DRAM timings, but at the same time I've never had a deep enough understanding of current to design a circuit that uses a logical signal to switch a 10v line using a FET. (this is how you do it btw: https://tinyurl.com/ydsgmdvh https://tinyurl.com/ydsgmdvh)

cushychicken 5y ago
There is a real case where someone could go a whole career in EE knowing a ton about DRAM timings and nothing about pulling up FET switches to the proper voltage. I know - I've met them!
- mcnugget 5y ago
  Real world effects of parasitics are underated. Found out the hard way that there's a whole lot of pain involved with hot plugging a battery into a board when there's a modular switch mode power supply onboard. Oh, you have a low esr ceramic cap on the input? Lol, the parasitic inductances of your wire and traces have formed a tank circuit and pushed the input voltage well above the unhappy voltage of something. K, you fixed that part, nope, lol, your inrush current is actually 15A because you had 68uF on the output of the smps and somehow you burnt out the internal fet of the smps module. Goddam nearly flipped a table.
  - cushychicken 5y ago
    Inrush is a real bitch. I make it a rule to include simple inrush current control circuits whenever I do DC input that sinks more power than, say, a USB cable. Lotsa surprise inductances out there. I've felt your pain re: inductance + input cap creating a resonant tank, too. That's a nasty surprise when you manage to create that resonance with your wiring.
    - mcnugget 5y ago
      The worst is when the other guys think you're crazy because they're not suffering the same problems because either the smps they have had a soft start or they overspeced the living crap out of their input stage. I gave up and just spend the 5$ for the IC that provides slew rate control, single IC with a single fet? Oh hell yeah.
gerdesj 5y ago
https://falstad.com/circuit/ https://falstad.com/circuit/ - there goes my afternoon ...
- squarefoot 5y ago
  Also, Micro-Cap is now free; not Open Source, still better than nothing. Windows only (although I seem to recall a Micro-Cap software running under the Mac Classic in the early 90s), but it works perfectly under Linux+WINE. http://www.spectrum-soft.com/index.shtm http://www.spectrum-soft.com/index.shtm
  - buescher 5y ago
    LTSpice is probably better for beginners, and my impression is that it is faster at the things it can do. Micro-Cap is really nice and does a whole lot more, though. And they're free, so you can have both!
buescher 5y ago
Just wait till you put a bigger load on your fet than that 100K resistor, try to PWM it, and discover the Miller effect.
dale_glass 5y ago
That's an absolutely trivial "how do you use a transistor" sort of example, though. If that's not covered I'd say it's because you're not learning electronics at all. You're just learning how a CPU talks to the RAM at a logical level, and what exactly you're actually doing when you're fiddling with the CAS latency setting in the BIOS.
- tinco 5y ago
  That's my point exactly, that my entire curriculum from highschool until my CS degree I always have gotten away with only logic design. I'm pretty sure at some point we've learned what a FET is and how it works, but I guess designing a circuit that involved one was deemed either too advanced, or not advanced enough. I even had courses in verilog. I'm pretty sure I'd do better designing a CPU in verilog, than designing a home automation controller. It's almost like a challenge of how close can you get to learning about electronics, without actually learning about electronics..
  - cmehdy 5y ago
    CS and EE are very different fields, there's lots to learn in each field. My curriculum was a blend of EE and applied maths/phys: I made carbon nanotubes in a lab, used quantum tunneling microscopes to look at atoms of gold, used VHDL to write games and generate the signals to display them in VGA, used control theory and electromechanical models to make a webcam rotate and move to track a face via PID, applied Kalman filters, etc.. But at no point did I learn how a compiler works, how linting works, what are fundamental differences between main programming paradigms, what data structures to pick for different kinds of problems, what are the fundamentals of an OS, how to be comfortable with LISPs, etc.. Once I was out of the academic environment without a PhD or a strong specialization (and just struggling to find any work), it was much more valuable to know binary trees and SQL than all of the EE stuff. So I was on the other end of what you experience, where at one point we covered without gaps quantum physics/chemistry --> barebones CPU, yet I wouldn't have known how to make something robust with it afterwards. And obviously, despite doing 'some' applied mathematics, any mathematician would look at what I did and probably roll their eyes at the amount of convenient assumptions made. There's just so much to learn out there that most of what we do in our lives is rely on abstractions, and it doesn't even have to be specific to computers: most people can use a bicycle without being able to draw a functional one[0]. [0] https://www.fastcompany.com/3059089/it-turns-out-its-almost-impossible-to-draw-a-bicycle https://www.fastcompany.com/3059089/it-turns-out-its-almost-...

by tinco 5y ago

cushychicken 5y ago

There is a real case where someone could go a whole career in EE knowing a ton about DRAM timings and nothing about pulling up FET switches to the proper voltage. I know - I've met them!

mcnugget 5y ago
Real world effects of parasitics are underated. Found out the hard way that there's a whole lot of pain involved with hot plugging a battery into a board when there's a modular switch mode power supply onboard. Oh, you have a low esr ceramic cap on the input? Lol, the parasitic inductances of your wire and traces have formed a tank circuit and pushed the input voltage well above the unhappy voltage of something. K, you fixed that part, nope, lol, your inrush current is actually 15A because you had 68uF on the output of the smps and somehow you burnt out the internal fet of the smps module. Goddam nearly flipped a table.
- cushychicken 5y ago
  Inrush is a real bitch. I make it a rule to include simple inrush current control circuits whenever I do DC input that sinks more power than, say, a USB cable. Lotsa surprise inductances out there. I've felt your pain re: inductance + input cap creating a resonant tank, too. That's a nasty surprise when you manage to create that resonance with your wiring.
  - mcnugget 5y ago
    The worst is when the other guys think you're crazy because they're not suffering the same problems because either the smps they have had a soft start or they overspeced the living crap out of their input stage. I gave up and just spend the 5$ for the IC that provides slew rate control, single IC with a single fet? Oh hell yeah.

gerdesj 5y ago

https://falstad.com/circuit/ https://falstad.com/circuit/ - there goes my afternoon ...

squarefoot 5y ago
Also, Micro-Cap is now free; not Open Source, still better than nothing. Windows only (although I seem to recall a Micro-Cap software running under the Mac Classic in the early 90s), but it works perfectly under Linux+WINE. http://www.spectrum-soft.com/index.shtm http://www.spectrum-soft.com/index.shtm
- buescher 5y ago
  LTSpice is probably better for beginners, and my impression is that it is faster at the things it can do. Micro-Cap is really nice and does a whole lot more, though. And they're free, so you can have both!

buescher 5y ago

Just wait till you put a bigger load on your fet than that 100K resistor, try to PWM it, and discover the Miller effect.

dale_glass 5y ago

That's an absolutely trivial "how do you use a transistor" sort of example, though. If that's not covered I'd say it's because you're not learning electronics at all. You're just learning how a CPU talks to the RAM at a logical level, and what exactly you're actually doing when you're fiddling with the CAS latency setting in the BIOS.

tinco 5y ago
That's my point exactly, that my entire curriculum from highschool until my CS degree I always have gotten away with only logic design. I'm pretty sure at some point we've learned what a FET is and how it works, but I guess designing a circuit that involved one was deemed either too advanced, or not advanced enough. I even had courses in verilog. I'm pretty sure I'd do better designing a CPU in verilog, than designing a home automation controller. It's almost like a challenge of how close can you get to learning about electronics, without actually learning about electronics..
- cmehdy 5y ago
  CS and EE are very different fields, there's lots to learn in each field. My curriculum was a blend of EE and applied maths/phys: I made carbon nanotubes in a lab, used quantum tunneling microscopes to look at atoms of gold, used VHDL to write games and generate the signals to display them in VGA, used control theory and electromechanical models to make a webcam rotate and move to track a face via PID, applied Kalman filters, etc.. But at no point did I learn how a compiler works, how linting works, what are fundamental differences between main programming paradigms, what data structures to pick for different kinds of problems, what are the fundamentals of an OS, how to be comfortable with LISPs, etc.. Once I was out of the academic environment without a PhD or a strong specialization (and just struggling to find any work), it was much more valuable to know binary trees and SQL than all of the EE stuff. So I was on the other end of what you experience, where at one point we covered without gaps quantum physics/chemistry --> barebones CPU, yet I wouldn't have known how to make something robust with it afterwards. And obviously, despite doing 'some' applied mathematics, any mathematician would look at what I did and probably roll their eyes at the amount of convenient assumptions made. There's just so much to learn out there that most of what we do in our lives is rely on abstractions, and it doesn't even have to be specific to computers: most people can use a bicycle without being able to draw a functional one[0]. [0] https://www.fastcompany.com/3059089/it-turns-out-its-almost-impossible-to-draw-a-bicycle https://www.fastcompany.com/3059089/it-turns-out-its-almost-...