On Sat, Mar 23, 2024 at 5:03 AM Erik Christiansen via Dng <
dng@???> wrote:

> On 22.03.24 06:25, o1bigtenor via Dng wrote:
> > On Fri, Mar 22, 2024 at 2:44 AM Steve Litt <slitt@???>
> > wrote:
> > > What does each temperature sensor output? A voltage? A current? Some
> > > sort of packet? Something else?
> > >
> >
> > There are a few different sensors that may be used - - - would depend
> > upon location. (Outdoor sensors need to be usable to at least -40C
> > and some humidity sensors need to be able to handle physical
> > condensation levels.)
>
> If the sensors output voltage or current, then some arduinos here and
> there could collect the data on their ADC input channels. Though 10 bit,
> only about 8 bits are really good, due to offsets, nonlinearities,
> quantisation, etc. The MSP430 has a 12bit(?) ADC, but I've no experience
> programming it.
>
> > >
> > > How many buildings are these congregated in? Are any outside? How close
> > > is each to the building housing your main computer?
> > >
> >
> > More than a few. Yes, Area covered is some few acres and distance to
> > main computer is in the order of circa 100 m.
>
> You can run RS485 a km over twisted pair, e.g. cat5 cable. Full duplex
> over two pairs. At 100m, data rate nudging 1 Mbps ought to be
> achievable, enough to track temperature variation, I figure.
> My recollection is that RS485 tranceivers tolerate ±7V DC offset between
> cable ends, avoiding need to run earth in the cable.
>
> It is possible to run analogue levels over 100 m distance, using 20 mA
> current loop converters. Then all the ADC is centralised, i.e. no need
> for little arduinos across the acres. But the latter could take other
> inputs like door switches - maybe it's important to know if a door has
> blown open, and the petunias will freeze in a couple of hours. (Better
> than a temp warning after the event.) And multiplexing many sensors into
> a digital stream on one cable pair saves a lot of cable installation.
>
>
Now if the more reasonably priced sensors actually used RS485 or
20 mA systems then this would be quite a bit more straightforward.
As it is - - - well at present for me anyway - - - its going to take a
ucontroller with something like a LAN8270 board (IIRC) attached to
the sensor to get the information transmitted. There is a severe trade
off between lower cost sensors and high cost sensors re: connectivity
options -- - - - unless you know of some options (would be very eager
to hear of such!).

> ...
>
> > >
> > > >So for data - - - do I use web based systems (Django/Python and their
> > > >attendant overheads) or something like WxWidgets (similar overheads)
> > > >or a SCADA kind of system (Proview) or might it be possible to pull
> > > >the data into something like storage (Postgresql database) and then
> > > >use something simple like a text based document (I'm not that into
> > > >'purdy pitchers') to display values with whatever control logic
> > > >running on different ucontrollers. (I used ledger-cli and like the
> > > >elegance of that system)?
> > >
> > > Why not a log file? You can then use very simple Python programs to
> > > create reports based on the log file.
> > >
> >
> > That's the third option that I listed.
>
> There is a classic app for presenting lots of distributed real-time data;
> SNMP. On linux, that's "net-snmp". Each sensor can be accessed as a
> point, or the snmp-walk command walks the tree to scan the lot. As a
> tree, there can be a branch for each barn/greenhouse/paddock or
> water/temp/humidity/doors if you don't care where they are. ;-)
>
> It's about two decades since I last used it, but ISTR that snmptrap
> allows sending of alarms on input excursions beyond limits. (But I'm
> nudging 70, so the wetware RAM isn't quite 100% on details now.)
> It supports authentication, so different users may be granted different
> access rights.
>
> It's easy to install a local instance on a linux box, to play with before
> going whole hog. A quick: $ apt-cache search snmp | more
> shows more than you probably want. A walk over the entire MIB
> (Management Information Base) was pretty brief. Here's the first bit:
>
> $ snmpwalk -v 2c -c public -m ALL localhost .1
> SNMPv2-MIB::sysDescr.0 = STRING: Linux dvalin 2.4.13-686 #2 Sun Oct 28
> 11:57:35 EST 2001 i686
> SNMPv2-MIB::sysObjectID.0 = OID: NET-SNMP-TC::linux
> DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (680720) 1:53:27.20
> SNMPv2-MIB::sysContact.0 = STRING: erik@???
> SNMPv2-MIB::sysName.0 = STRING: dvalin
> SNMPv2-MIB::sysLocation.0 = STRING: Earth
> SNMPv2-MIB::sysORLastChange.0 = Timeticks: (33) 0:00:00.33
>
> The MIB is defined in ASN.1 notation, which you put through the supplied
> MIB compiler. Pushing data into the MIB from distributed sensor data
> collection clusters looks to be partly done for arduino:
> https://www.arduino.cc/reference/en/libraries/snmp/
> A bit of googling might reveal more yet.
>
> I have a list of SNMP books, but that file is 22 years old, so maybe of
> limited usefulness now.
>
> > >
> > > >
> > > >Suggestions - - - (yes I know I'm nuts) ideas - - - etc welcome - - -
> > > >please?
> > >
> > > Not nuts at all. This is the first time I've heard of an IoT system
> > > that solves an actual problem.
> > >
> > >
> > Commercial (read industrial) control systems are yammering about how
> > they're IoT - - - except they always have been - - - grin!
>
> That's "Introduction of Trouble", isn't it? How good is the
> authentication? Does it involve more than one protocol and a port or
> two? Too many doors makes things harder to defend. (And who wants to
> turn up to work to find all the cabbages frozen solid?)
>
> I've designed a little three channel LED lamp dimmer, networked over
> RS485, for my off-grid solar powered rural build. Collection of
> temperature data was to be next cab off the rank. Because the uC has
> only 32 registers, 2kB of codespace, and 128 bytes of RAM, the protocol is
> pretty basic DIY. (Why overdo the hardware, when not needed?) I'll have to
> finish the networking part of the firmware, but am sidetracked on
> whipping up a power diverter for the Hot Water Service to only use
> surplus solar power, detectable by the battery inverters shifting the
> (off-grid) supply frequency up toward 52.5 Hz to throttle the solar
> inverters. Burst fire of whole power cycles, switched on zero crossings,
> ought to minimise interference. (You can see why the 3/4 finished
> project had to be sidelined, with fun like that to fiddle with.)
>
> The 7 kW EV charger has an automatic mode to also use only surplus solar
> power, but it won't engage. Not impressive on a commercial unit of
> non-trivial cost. (The BEV runs on 100% fossil-free photons. Crikey,
> what a feeling! )
>

Hmmmmmm - - - solar - - - very useful if you have lots of solar energy - -
-
here - - - not so much from end of Nov to mid Feb absolutely not unusual to
have 30+ days that are overcast - - - means when needs is high there is
little
available energy.

Some very very interesting ideas - - - I do understand that I'm not doing
anything real new - - - rather I'm trying to do more of this as DIY rather
than
opening my wallet a long ways!

Regards

>
>