On Sat, May 13, 2023 at 2:42 PM Simon <linux@???> wrote:
>
> o1bigtenor via Dng <dng@???> wrote:
>
> > I am in the beginning throes of an embedded system (SoC, and/or
> > microcontroller) design.
> >
> > Have been reading somewhat on the use of RTOS vs and OS (thinking
> > perhaps FreeRTOS and Devuan). My initial problem is a weighing 'cell'
> > where I'm weighing liquids being deposited in a 'jar'.
> > (A second would be items deposited (and then removed in stages) from a
> > 4 wheel cart.)
> >
> > How does one decide when a RTOS is more appropriate than an OS?
>
> As already says, it comes down to “if I want X to happen at time Y, how reliable do I want Y to be ?”
> These days, something as cheap as a Pi runs so fast that many tasks that would have needed an RTOS back when I used to be involved with this stuff can be done “reliably enough” without going “hard” RT. A secondary question is “does someone die or lose limbs if it goes wrong ?” - which also influences the decision since you’d never pass a safety case for something where the answer is “yes” with a raspberry pi and a generic OS.


Well - - - - given that there are lots of 'soft' robotics (cobots)
around someone has come up with solutions.
Hmmmmmm - - - - another thing to look into - - - but then I need
robotics for one of the functions so
this was a direction that I was already looking into - - - -just
expanded the 'need' case - - - grin.

Thanks - - - for the info.
>
> And as part of the mix, you have trade-offs. So while you could just chuck in (say) an ARM SoC and use brute force to create near-enough RT operation, you might decide that the reliability downside of running millions of lines of code to emulate a few TTL chips is too much - and so you’d be better using something smaller & simpler, and then having to do more low-level stuff to make things work.
>
> In other words, there isn’t “an” answer. What you’d have to do is make a list of options, filter them to remove any that wouldn’t meet some non-optional requirement, and then list the pros & cons of each so you can decide which is the optimum choice.
>
>
>
> >> PoE over CAT-5 can deliver 5V or 12V to multiple remote locations. Other options include solar and battery
> >
> > Hmmmmm - - - just did a little playing with ampacity charts
> > seems at 5V with 2.5 A (not that big a draw imo) well I need to run 10
> > ga if I'm running 5 m.
>
> I wouldn’t run 5V over any distance - you’ve little tolerance for volt drop, and it’s hard to provide any form of protection against being connected to the wrong voltage.
> Using passive PoE (basically just stick power on two of the wires) you can use 12V or 24V - with 24V you’d be down to just under 1/5A which is a lot more manageable. Not only that, but (assuming you a switching down-converter) you get to compensate for any volt drop in the conversion.
> Active PoE (e.g. 803.11AF) uses 48V. Also, the power sourcing equipment does not apply power unless it sees the right signal (basically a resistor), and provides protection against connecting stuff that wasn’t expecting power coming down the wires.

Hmmmmmm - - - - sounds like 12V for short runs, 24V for runs up to
say a couple m and
48V for at least up to 5 m - - - - that's off the cuff and will need checking.
Then I will need a buck transformer at each location. (Oops - - -
costs just went up
some more - - - grin!!! - - - - as the 'interesting factor goes up the
$$$$ factor is
escalating even faster!)
>
> >>
> >> If you standardise on CAT-5 then you can run most protocols and power in 1 cable.
> >
> > Given the above - - - - there is a lot more thinking through that will
> > need to happen!
>
> Yes, lots to think about.
>

Thanking you for your input.
I think that I'm about ready to do some more 'lock down' in the thinking.

Wondering - - - - as a question to you Mr Simon and the other responders - - -
any interest in reports as I get stages working?

Thank you for being an interesting bunch of peoples!!!!!!!!!!!!

(Back to the bear pit!!!! (grin!))