Low power PC with at least 2 RS232 ports

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kiwigander

231 posts

Master Geek

#279587 24-Oct-2020 21:35

I'm in the market for an energy-efficient computer with 2 RS232 ports.

The purpose of this machine is to transmit data from my weather station to my web page (on a server at my ISP), likewise with data from my remote area power system (RAPS), and to run Logitech Media Centre (i.e. to stream audio through my Squeezebox).

Presently I'm managing with a 13-year-old Dell laptop, but with its only RS232 interface tied up by the weather station, it can't be interfaced to my RAPS; besides, it is 13 years old. It's also consuming 12 or 13 watts 24/7, which consumption I'd like to reduce if possible, being off grid.

Nothing suitable seems to be available through ordinary NZ retailers online and off. (Please correct me if I'm wrong here.)

My choice seems to be between a USA firm offering a fanless mini-PC for over USD 500, and a multitude of firms in the PRC, either through AliBaba or Amazon.

Can anyone suggest a reliable manufacturer or retailer for this kind of item?

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1230 posts

Uber Geek

#2591539 24-Oct-2020 23:42

RS-232 ports on PCs these days are normally done using a USB RS-232 device. Some motherboards do still have one RS-232 connector, but two is rare. And you have to get the right cable to bring it out the back - I do not know of any new PCs except industrial ones that will actually have an RS-232 DB-9 or DB-25 connector.

What exactly to you need to do? Would a tiny device like one of the ESP32 modules do the job? There are ones with WiFi builtin, and they all have at least one serial port, although it is usually TTL or even lower levels, so would need level shifter/buffer chips to connect to real RS-232. But there are likely off the shelf boards that will have one or more real RS-232s - I have not looked to see what is available. ESP32s can be extremely low power, but having to have real RS-232 voltages can mean you will have a problem providing them at very low power. The right ESP32 is able to provide a web server, so it should be able to do what you need unless there is some serious number crunching to be done.

michaelmurfy

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#2591546 25-Oct-2020 00:58

Something else - does this software require Windows or can it be run on Linux? How about something like a Raspberry Pi w/ a couple of USB --> RS232 dongles?

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K8Toledo

1014 posts

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#2591549 25-Oct-2020 05:43

kiwigander: I'm in the market for an energy-efficient computer with 2 RS232 ports.

The purpose of this machine is to transmit data from my weather station to my web page (on a server at my ISP), likewise with data from my remote area power system (RAPS), and to run Logitech Media Centre (i.e. to stream audio through my Squeezebox).

Presently I'm managing with a 13-year-old Dell laptop, but with its only RS232 interface tied up by the weather station, it can't be interfaced to my RAPS; besides, it is 13 years old. It's also consuming 12 or 13 watts 24/7, which consumption I'd like to reduce if possible, being off grid.

Nothing suitable seems to be available through ordinary NZ retailers online and off. (Please correct me if I'm wrong here.)

My choice seems to be between a USA firm offering a fanless mini-PC for over USD 500, and a multitude of firms in the PRC, either through AliBaba or Amazon.

Can anyone suggest a reliable manufacturer or retailer for this kind of item?

RS232 was superseded by USB eons ago.

One RS232 port is required at most, possibly for the weather station (what are the specs?). RS232 - USB cable might work, or I can send you a PCI serial port adapter (for adding serial ports to newer machines).

SirHumphreyAppleby

2844 posts

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#2591555 25-Oct-2020 07:31

If you don't mind one of the ports being on an internal header (possibly requiring soldering), will run Linux or *BSD and don't need video, then I would recommend the PC Engines products.

The APU2 will run on 6-10W. Their older ALIX boards use about 5W.

They can be purchased in NZ, but it's a lot cheaper to import these yourself from Switzerland. I have an old ALIX if you are interested (need to confirm if the second COM port can be used).

K8Toledo:

RS232 was superseded by USB eons ago.

I disagree. USB RS232/RS485 adaptors have very limited functionality and can't be used as a replacement for real ports in many cases.

andrewNZ

2487 posts

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#2591571 25-Oct-2020 08:35

usb-232 is probably the best option. I use them frequently to talk to PLC's and other automation equipm. I've only seen one thing that doesn't work with one, and that's a very old rs485 device.

Jaycar have them and they're good. They use genuine Prolific chips from what I can tell.

cyril7

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#2591581 25-Oct-2020 09:28

USB rs232 is the way to go use it daily on a wide range of devices, mainly networking gear ie routers and switches, ne er had an issue. Even works on my chromebook via beagle term.

Cyril

sbiddle

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#2591588 25-Oct-2020 09:46

Whether USB to RS232 adapters will work or not depends on the actual device. 99% of devices that need a RS232 port will work fine over a USB to RS232 adapter.

I have several pieces of hardware that use RS232 ports but don't actually use the RS232 spec as such but communicate using a hack involving using CTS and DSR pins. These won't work on USB to RS232 adapters, and they also won't work on some newer PCs even with a RS232 port as the port isn't a "true" RS232 port but a physical port that's effectively doing RS232 emulation via a different bus.

In the case of the OP both use cases would highly likely be standard RS232 serial devices so the simplest and most cost effective option would be any sort of mini PC and USB to RS232 adapters. I managed to pick up a few 2nd hand Giada mini PC's a few months ago that have dual serial, but for new hardware there are pretty limited options.

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Apsattv

2389 posts

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#2591938 25-Oct-2020 22:27

Couldnt you just use an old chromebook with a couple of USB r232 adapters

Is the main issue power usage?

Maybe even a small android stb if the hardware will support USB r232.. buy a usb converter and experiment

K8Toledo

1014 posts

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#2591939 25-Oct-2020 22:31

SirHumphreyAppleby:

If you don't mind one of the ports being on an internal header (possibly requiring soldering), will run Linux or *BSD and don't need video, then I would recommend the PC Engines products.

The APU2 will run on 6-10W. Their older ALIX boards use about 5W.

They can be purchased in NZ, but it's a lot cheaper to import these yourself from Switzerland. I have an old ALIX if you are interested (need to confirm if the second COM port can be used).

K8Toledo:

RS232 was superseded by USB eons ago.

I disagree. USB RS232/RS485 adaptors have very limited functionality and can't be used as a replacement for real ports in many cases.

Totally irrelevant to my quoted comment RS232 was superseded by USB?

Edit: I see what you mean - I specifically meant 9 pin serial I/O ports, not the bus or board headers. ;) I get SPI is still used for programming routers etc.

I use an FTDI RS232-USB adapter for programming my BMW (I do mean programming, not just scanning). Knock off versions with fake FTDI chips are often sold on Aliexpress etc.

The second issue is newer FTDI drivers won't automagically install with copied chips due to device ID missing. The drivers must be force installed through device manager.

kiwigander

231 posts

Master Geek

#2591949 26-Oct-2020 00:17

Thanks for all the advice.

I'm not confident that the data centre of my power system can easily be interfaced to USB. It's even older than the Dell laptop and its RS232 interface requires power from the computer to which it's going to be connected.

It looks as if the weather station can cope with an RS232-USB converter. I may try that as a first step - although I now see there's a dual RS232 interface hat for the Raspberry Pi, which might be an answer. (Funny how you find things after you've given up looking for them, ask for help, then look again.)

The weather station display-and-publish software (weewx) runs in Linux, as does the Logitech Media Server. And whatever application will display and publish the status of the power system will be written to run in Linux as well.

noroad

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#2591959 26-Oct-2020 08:52

kiwigander: I'm in the market for an energy-efficient computer with 2 RS232 ports.

Here you go -

https://xcyminipc.aliexpress.com/store/all-wholesale-products/817796.html?spm=a2g0o.store_home.pcShopHead_5900306.1

I use these as mini servers, always worked perfectly.

Behodar

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#2591964 26-Oct-2020 09:48

kiwigander: although I now see there's a dual RS232 interface hat for the Raspberry Pi, which might be an answer.

That could do the trick. The Pi has native serial and just lacks the physical port, so you're not going via USB.

kiwigander

231 posts

Master Geek

#2591993 26-Oct-2020 12:20

@noroad:

Here you go -

https://xcyminipc.aliexpress.com/store/all-wholesale-products/817796.html?spm=a2g0o.store_home.pcShopHead_5900306.1

I use these as mini servers, always worked perfectly.

Thank you. I've just placed my order. I had seen similar units elsewhere in the Aliverse but wondered about the quality. Fingers crossed that my experience will be as good as yours.

kiwigander

231 posts

Master Geek

#2629071 1-Jan-2021 22:34

Apology for resurrecting a dormant thread, but here's an update.

I ordered one of the mini-servers described by @noroad from AliExpress, and it arrived in about 3 weeks. I didn't encounter the shipping dramas many on this board have described. That's the good news.

The bad news:

1. The RS-232 ports don't work.

2. When I check the mini-server's RAM with memtest86+ (latest version, accompanying the Linux Mint 20 XFCE distribution) it gets a few seconds into the first go-round and the entire server freezes, and only powering off and on does anything.

Re 1, I notified XCY of the problem, and after some delay they told me to short 2 pins on an RS-232 port and check -- something. I've asked for clarification, but I don't see how I can plug my weather station's serial cable into a DE9 port that has a shunt shorting two pins together.

Re 2, this I discovered while waiting for a reply to my question about 1.

I do not foresee a happy outcome with this unit.

I've got both the old server and the new mini-server working well with the weather station via an RS-232<=>USB adapter, so the need for RS-232 ports on the new mini-server is now in doubt.

@noroad, have you, or has anyone watching this thread, had to make a warranty claim with this outfit? Any tips?

hio77

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#2629075 1-Jan-2021 22:38

warranty and aliexpress isn't ever a fun game...

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