Comment by dragontamer | Hacker News Reader

Comment by dragontamer | Hacker News Reader

Parent Full thread

http://sparks.gogo.co.nz/assets/_site_/downloads/smd-discret...

> Jellybean is a common term for components that you keep in your parts inventory for when your project just needs “a transistor” or “a diode” or “a mosfet”

-----------

For many hobbyists, a Raspberry Pi or Arduino is a good example of a Jellybean. You buy 10x Raspberry Pis and stuff your drawer full of them, because they're cheap enough to do most tasks. You don't really know what you're going to use all 10x Rasp. Pi for, but you know you'll find a use of it a few weeks from now.

---------

At least, in my Comp. Engineering brain, I think N2222 transistors or 3904-transistors, or the 741 Op-amp. There are better op-amps and better transistors for any particular job. But I chose these parts because they're familiar, comfortable, cheap and well understood by a wide variety of engineers.

Well, not the 741 OpAmp anymore anyway. 741 was a jellybean back in the 12V days. Today I think 5V compatibility has become the standard voltage (because of USB). So 5V op-amps are a more important "jellybean".

I don't know how old you are, but the 741 was obsolete in the 1980s. It sticks around in EE textbooks because it's such an easy way to demonstrate problems with op-amps... high input current, low gain-bandwidth product, low slew rate, etc.

I think your jellybean op-amps would more likely be TL072, LM358, or NE5532.

Old, beaten up textbooks from the corner of my neighborhood library was talking 741 back in the 2000s, when I was in high school and started dabbling around with electricity more seriously.

Maybe it was fully obsolete by that point, but high school + neighborhood libraries aren't exactly filled with up-to-date textbooks or the latest and greatest.

I remember that Radio Shack was still selling kits with 741 in them, as well as breadboards and common components... 12V wall-warts and the like. Online shopping was beginning to get popular, but I was still a mallrat who picked up components and dug through old Radio Shack manuals into 2005 or 2006.

It was the ability to walk around, and see those component shelves sitting there in Radio Shack that got me curious about the hobby and start researching it. I do wonder how modern children are supposed to get interested into hobbies now that malls are less popular (and electronic shops like Radio Shack are basically disappeared).

------------

I don't remember what we used in college. I knew that I was more selective and understood the kinds of problems various OpAmps had back then. Also you're not really rich enough to invest into a private stockpile of chips, and instead just use whatever the labs are stocked with in college.

LM358 is the jellybean that I keep in my drawer today. If you're curious. Old habits die hard though, I still think 741 as the jellybean even though it really is obsolete today.

I've got a tube each of 358's and 1458's (dual version) in my parts supplies. But my microwave stuff is finding them lacking.

+1 for LM358

Yeah, I got about a hundred of them for $5 total when my Radioshack went under. Very jellybean.

That's the one my text book often referred to.

I'm not sure if this is the same as what you mention with 12V vs 5V, but Intel is pushing a 12V standard PSU design that is also used by the new Nvidia Founders Edition GPUs:

https://www.intel.com/content/dam/www/public/us/en/documents...

So when you work with analog electronics, you learn that voltage is your friend. Playing with +/- 12V (a 24V range) for "analog logic" is innately cleaner than playing with 0V to 5V (5V range).

Lets say you make a design that has +/- 1V error. On the 5V circuit, that's 20% error. But on the +/-12V circuit, it is only 4.1% error. (Going much better than 5% or 1% error is nonsensical. Most resistors you'll buy are 5% error, and capacitors are maybe +/- 20% error). So you can see, +/-1V error is acceptable on +/-12V circuits, but maybe unacceptable on 5V circuits.

If precision is important, there are 1% or 0.1% resistors available, as well as matched-resistors (which have say 1% error, but all the resistors have the same degree of error, so your "proportions" remain consistent. You can manually-match resistors together with an accurate ohm-meter as well)

As such, +/- 12V is simply easier to make "precise" electronics on. Of course, the downside is that you've got leakage all over the place (more voltage means more power-draw)

---------

But now its 2021. Most parts, even extremely cheap "Jellybean" parts like the LM358, have low errors and low-bias. And USB's popularity as a 5V delivery mechanism has grown, everyone has a USB plug somewhere to use as the basis of electricity experiments.

So while electronic engineers way back played with +/-12V, today the assumption is that you play with 0V to 5V.

My interpretation: Small buck converters are cheap and efficient, and so many parts need different voltages anyway (1.8V, 1.5V, 1.2V, etc.), that what you want to do is distribute the 12V from the main PSU and then locally convert it to the voltage you need.

If you are already putting buck converters everywhere, it makes sense to raise the voltage coming from the PSU, because you can reduce the current supplied by the PSU. Only the power supply will be running at 12V, almost everything else will be running at a lower voltage. (Would you rather supply 120W at 12V/10A or 5V/24A?)

Reply on news.ycombinator.com