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Forum Index : Microcontroller and PC projects : Spa Controller

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Tinine
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Joined: 30/03/2016
Location: United Kingdom
Posts: 1527
Posted: 05:31pm 01 Dec 2019
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  Turbo46 said  If I am understanding the above circuit correctly, the driver IC is only enabled when the Serial Out (Tx) pin is low and disabled when it is high (plus a short delay caused by the R/C circuit). As it says "a driver is enabled for only an average of half the time required to transmit a word".

If the data was 'FF' Hex, the driver would be only enabled for the START bit and disabled for the rest of the word except for a short pulse at the beginning or the first '1' bit. The RS485 A/B signal lines would be tri-state for every '1' bit transmitted.

Surely this arrangement would be highly susceptible to noise? If it works at all I can't see how it would work reliably - especially over long distances. The board shown in Phil23's first photo is a little more complex.

Not explained above is that the two Schmidt trigger gates in series with the Tx and Rx lines will add a little propagation delay to the signals so that little (if any) of the START and other '0' bits are lost.

Please correct me if I am wrong.

Bill


Bill, the way I read it; the TX is only gating itself with the enable.

Not totally sure why the delay is required, TBH...I will read again later.
 
Tinine
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Posted: 05:38pm 01 Dec 2019
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FWIW:I always start my transmissions with AA (10101010).

Regards,

Craig
 
Phil23
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Joined: 27/03/2016
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Posted: 10:36am 02 Dec 2019
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Ended up finding 3 of the Auto switching modules in one of my parts drawers.

Good thing is that I can directly swap one out for the HC-11 that is currently on Com1 of the heat pump controller, and not need to worry about changes to the board to accommodate the DE pin.

Did also find a good data source on the module, including schematic here...

https://protosupplies.com/product/scm-ttl-to-rs-485-interface-module/

Cheers.
 
Turbo46

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Joined: 24/12/2017
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Posted: 06:57pm 02 Dec 2019
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Thanks for that Phil23. The circuit is similar to that posted by Tinine but the 27uS delay has been extended out to over 5mS! It looks like a good device, well protected  and documented.

Considering that I bought the MAX485 chip locally for $5.95 the price is good too.

I have used one of these devices on my laptop to talk to RS485 devices using DOS MMBasic. It must use a similar automatic direction control.





Bill
Keep safe. Live long and prosper.
 
Phil23
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Posted: 07:59pm 03 Dec 2019
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Have the same USB one too.

Found it very useful for monitoring the bus when I was setting up the coms between the MM & the Modbus meters.
 
Phil23
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Posted: 09:21am 20 Nov 2022
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So 5 years down the track it's died.
Relied too long on my Prototype hardware & never quite got to a soldered board.
(Strip would do it).

So in the interim I'm controlling the circulation pump with a smart switch via Home Assistant.

Basically getting data, (Solar Energy, Air Temp & Water Temp) from an Ecowitt Weather
Station that Home Assistant integrates with.

Control & making the most of the Sun is very poor in comparison to my MM build, but I do like the data I can see in HA, as well as the presentation.

Which gets me thinking.
The Pico Pi W, that has popped up recently.
Will it be offering anything interesting in the Micromite World?

The thought of MQTT, which I know little about sounds like an opening to outside communications.

Could scrap my who;e MM build, but think that's the wrong way to go.
Coms to the outside world though would be a huge addition to the MM World.

Cheers

Phil
 
TassyJim

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Joined: 07/08/2011
Location: Australia
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Posted: 08:53pm 20 Nov 2022
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Hi Phil,

No MMBasic for the pico W.

PS.
Your Lightning detector controller needs a firmware update.
The GPS has suffered from a week 1024 rollover.
Plenty of info on the Blitz forum.

Don't get caught by blaming the GPS antenna before checking the forum (like i did).

Jim
Edited 2022-11-21 06:54 by TassyJim
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bigmik

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Joined: 20/06/2011
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Posted: 11:15pm 20 Nov 2022
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G’day All,

@phil23,
2m will be a piece of cake with serial at 115200 baud. I tested it over 11m but others have successfully ran 50m

See this thread >> Link <<

@tinine,
With RS485 GND is not needed between the nodes, only the differential pair(s)

Kind regards,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
Phil23
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Posted: 04:35am 21 Nov 2022
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Thanks Jim,

And Yes I was browsing down the road of a replacement GPS Receiver.
Was blaming years in the weather for it's demise.

Saw an upgrade was mentioned, but got Gun Shy of doing it while thinking I had a dead GPS. Didn't read on for specifics, but am aware the roll over has killed a few things.

An Old Garmin eTrex & the GPS Speed Controller in my Boat.

Boat Controller manages the throttle position & RPM & maintains Speed to timed 0.01 Seconds over a 16.08 Second run, with timing checked at 7 distance points along the way.....
 
Mixtel90

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Joined: 05/10/2019
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Posted: 07:30am 21 Nov 2022
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In theory, GND isn't needed for RS485...
In actual fact you tend to get problems if it's omitted. It's quite true that the data is carried in the differential signal, but if both lines drift far enough away from GND you hit the common mode limit of the chips. At that point you start to lose either the "1"s or the "0"s as they can no longer be decoded. It can even cause damage in some cases. This is why, for long distance RS485, you need full diode and voltage protection at both ends.
Over short distances, in reasonably electrically quiet conditions you'll usually get away without the GND (providing the transmitter and receiver are either galvanically isolated from each other in some way or their GND potentials are close). For long distances it's very unwise to run without GND and balancing resistors, as well as termination resistors.
Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs
 
bigmik

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Posted: 09:11am 21 Nov 2022
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Hi Mick (the other one),

When I was employed in the racing game we ran RS485 up-to 1500m.

The server in the control room had mains earth connected to logic GND

We ran 5 pair shielded CAT3 cable, on that cable shield was Mains GND, the 10 wires were

Channel A
Tx+
Tx-
Rx+
Rx-

Channel B
Tx+
Tx-
Rx+
Rx

The other 2 wires were both connected at the servers (2 servers channel A and Channel B) GND and was passed through all of the daisy-chained data cabling infrastructure.

However the terminal feed leads did not have these GNDs nor the shield connected from the infrastructure cables to the terminal so electrically only the dual differential wires were connected from the servers to the terminals.

You could argue that the remote terminals (we had up to 16 on each line) picked up GND through the EARTHING point and you have a case I suppose. We often had data errors causing issues on the long runs so I designed an opto isolation box that removed all electrical continuity from its input to its output, it used a transformer with 2 secondary windings so input and output had totally isolated power supplies, this cleaned up the data loss and IMHO it proves that the data lines alone is all that is needed.

Towards the end of my career we started to use unshielded cat 5 cable for the temporary runs could be a couple of hundred meters or more and these had no GND or Earth connections just the 8 differential lines.

Now all of the above is on 4 wire RS485, I have no experience with 2 wire, perhaps this is different.

Kind Regards,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
Mixtel90

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Posted: 09:50am 21 Nov 2022
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Once you isolate with transformers or optocouplers the problem has gone. The driver side can float independently to the line side so will always stay within the common mode range. :)
Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs
 
bigmik

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Posted: 10:11am 21 Nov 2022
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Mick,

the opto isolator box was only used in extreme situations, I was meaning to point to the fact we used cat 5 with no grounds or earths over hundreds of metres.

Anyway as per all of these things YMMV.

Take care,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
Phil23
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Posts: 1662
Posted: 09:03pm 21 Nov 2022
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Thanks again @TassyJim

Just updated it to 9.4.
Haven't read all the treads about the issue, but it now has a lock,
just not showing a correct date & assume the time is GMT.

Is the firmware in the actual GPS Receiver able to be updated too.
Assume that's where the root of the issue lies.

Not sure how that would be done with this type of device that communicates over a single Coax feed.




Also just read the intro of Peter's post Re the PicoW firmware.

Last 3 years have had a lot of turmoil & little time to play with devices, but hopefully settling back to normal over the next six months.

Cheers.
 
TassyJim

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Posted: 01:17am 22 Nov 2022
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If you don't use the blitz as a NTP server, you don't have to worry about the date being out. The time is correct.

If you do want to use the Blitz as an NTP server like I do, you have to update the GPS firmware.
The full instructions are on the forum but a simple todo:
You power the Blitz from your PC so you can use the USB to serial built in to the unit. You also need TCPIP access.

You have to install some STM drivers. If your PC has been used for a few other STM chips, you may have the driver already. The W8 driver works for W10 and W11.

Via the web interface, turn the USB port 'on'
Run the PowerFlash from the globaltop zip
Update to V3.8 and all will be well.

A lot of users seem to have problems but a lot of users are not very PC savvy.


GlobalTop FlashTool.zip

stm32102.zip

Jim
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