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devel / comp.arch.embedded / Re: Boxed MCU with RS-232 Port

SubjectAuthor
* Boxed MCU with RS-232 PortRick C
+* Re: Boxed MCU with RS-232 PortPaul Rubin
|`* Re: Boxed MCU with RS-232 PortRick C
| +* Re: Boxed MCU with RS-232 PortPaul Rubin
| |`* Re: Boxed MCU with RS-232 PortRick C
| | `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |  `* Re: Boxed MCU with RS-232 PortRick C
| |   +* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |`* Re: Boxed MCU with RS-232 PortRick C
| |   | `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |  `* Re: Boxed MCU with RS-232 PortRick C
| |   |   `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |    `* Re: Boxed MCU with RS-232 PortRick C
| |   |     `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |      `* Re: Boxed MCU with RS-232 PortRick C
| |   |       `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |        `* Re: Boxed MCU with RS-232 PortRick C
| |   |         `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |          `* Re: Boxed MCU with RS-232 PortRick C
| |   |           `- Re: Boxed MCU with RS-232 PortPaul Rubin
| |   `* Re: Boxed MCU with RS-232 PortAndrew Smallshaw
| |    `* Re: Boxed MCU with RS-232 PortRick C
| |     `* Re: Boxed MCU with RS-232 PortAndrew Smallshaw
| |      +- Re: Boxed MCU with RS-232 PortAndrew Smallshaw
| |      `- Re: Boxed MCU with RS-232 PortRick C
| `- Re: Boxed MCU with RS-232 PortDavid Brown
+* Re: Boxed MCU with RS-232 PortTheo
|`* Re: Boxed MCU with RS-232 PortPaul Rubin
| `* Re: Boxed MCU with RS-232 PortTheo
|  +* Re: Boxed MCU with RS-232 PortDon Y
|  |`* Re: Boxed MCU with RS-232 PortRick C
|  | `* Re: Boxed MCU with RS-232 PortPaul Rubin
|  |  `* Re: Boxed MCU with RS-232 PortRick C
|  |   `- Re: Boxed MCU with RS-232 PortPaul Rubin
|  +* Re: Boxed MCU with RS-232 PortGrant Edwards
|  |+- Re: Boxed MCU with RS-232 PortRick C
|  |`- Re: Boxed MCU with RS-232 PortDon Y
|  `* Re: Boxed MCU with RS-232 PortRick C
|   +* Re: Boxed MCU with RS-232 PortTheo
|   |+- Re: Boxed MCU with RS-232 PortRick C
|   |`* Re: Boxed MCU with RS-232 PortPaul Rubin
|   | +* Re: Boxed MCU with RS-232 PortDon Y
|   | |`- Re: Boxed MCU with RS-232 PortDon Y
|   | `- Re: Boxed MCU with RS-232 PortTheo
|   `* Re: Boxed MCU with RS-232 PortHerbert Kleebauer
|    `* Re: Boxed MCU with RS-232 PortRick C
|     `* Re: Boxed MCU with RS-232 PortDimiter_Popoff
|      `* Re: Boxed MCU with RS-232 PortRick C
|       +- Re: Boxed MCU with RS-232 PortDimiter_Popoff
|       `* Re: Boxed MCU with RS-232 Portantispam
|        `* Re: Boxed MCU with RS-232 PortRick C
|         `* Re: Boxed MCU with RS-232 Portantispam
|          `* Re: Boxed MCU with RS-232 PortRick C
|           `* Re: Boxed MCU with RS-232 PortRick C
|            `* Re: Boxed MCU with RS-232 PortRick C
|             `* Re: Boxed MCU with RS-232 PortDimiter_Popoff
|              `- Re: Boxed MCU with RS-232 PortDon Y
+* Re: Boxed MCU with RS-232 Portpozz
|`- Re: Boxed MCU with RS-232 PortRick C
+* Re: Boxed MCU with RS-232 PortRick C
|+* Re: Boxed MCU with RS-232 PortPaul Rubin
||`* Re: Boxed MCU with RS-232 PortRick C
|| +* Re: Boxed MCU with RS-232 PortRick C
|| |+* Re: Boxed MCU with RS-232 PortTheo
|| ||`- Re: Boxed MCU with RS-232 PortRick C
|| |`* Re: Boxed MCU with RS-232 PortPaul Rubin
|| | `- Re: Boxed MCU with RS-232 PortRick C
|| `* Re: Boxed MCU with RS-232 PortPaul Rubin
||  `* Re: Boxed MCU with RS-232 PortRick C
||   +- Re: Boxed MCU with RS-232 PortPaul Rubin
||   `* Re: Boxed MCU with RS-232 PortHans-Bernhard Bröker
||    +* Re: Boxed MCU with RS-232 PortTheo
||    |+* Re: Boxed MCU with RS-232 PortRick C
||    ||+- Re: Boxed MCU with RS-232 PortTheo
||    ||+* Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||`* Re: Boxed MCU with RS-232 PortRick C
||    ||| `* Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||  +- Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||  `* Re: Boxed MCU with RS-232 PortRick C
||    |||   `* Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||    `* Re: Boxed MCU with RS-232 PortRick C
||    |||     `- Re: Boxed MCU with RS-232 PortPaul Rubin
||    ||`* Re: Boxed MCU with RS-232 PortDon Y
||    || `* Re: Boxed MCU with RS-232 PortRick C
||    ||  +- Re: Boxed MCU with RS-232 PortDon Y
||    ||  `* Re: Boxed MCU with RS-232 PortGeorge Neuner
||    ||   +* Re: Boxed MCU with RS-232 PortRick C
||    ||   |+* Re: Boxed MCU with RS-232 PortJim Jackson
||    ||   ||+* Re: Boxed MCU with RS-232 PortDon Y
||    ||   |||+* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||`* Re: Boxed MCU with RS-232 PortDon Y
||    ||   |||| `* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  +* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |`* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  | `* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |  `* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  |   `* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |    +* Re: Boxed MCU with RS-232 PortJim Jackson
||    ||   ||||  |    |+- Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  |    |`- Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |    `* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  `* Re: Boxed MCU with RS-232 PortDavid Brown
||    ||   |||`- Re: Boxed MCU with RS-232 PortRick C
||    ||   ||`- Re: Boxed MCU with RS-232 PortRick C
||    ||   |`* Re: Boxed MCU with RS-232 PortDon Y
||    ||   `* Re: Boxed MCU with RS-232 PortDon Y
||    |`- Re: Boxed MCU with RS-232 PortHans-Bernhard Bröker
||    `* Re: Boxed MCU with RS-232 PortRick C
|`* Re: Boxed MCU with RS-232 PortHerbert Kleebauer
+- Re: Boxed MCU with RS-232 PortRick C
`* Re: Boxed MCU with RS-232 PortUwe Bonnes

Pages:1234567
Boxed MCU with RS-232 Port

<f1d09e6f-688d-4a73-9a37-a4a58de6a3a9n@googlegroups.com>

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Subject: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Tue, 17 Jan 2023 15:24 UTC

The unit only really needs one serial port, but it is more convenient to have two connectors, so I guess it needs to ports. One port will only receive and the other only transmit, no handshaking.

The function is pretty simple. A sensor sends a line of about 50 chars, at 9,600 bps, once per second. This box counts 20 lines and adds a header. So nothing fancy is required of the MCU. There are parameters set when starting operation.

The main thing I'm having trouble finding, is this needs to be in a box as a unit, not a board and a box to be assembled. Google hasn't been much help returning all sorts of things that aren't useful.

Anyone know of such a box? The programming might be contracted out, if you are interested. There's a prototype using an Arduino nano, but some of them are flaky and it would not hurt to start over from scratch.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

<87k01lufem.fsf@nightsong.com>

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From: no.em...@nospam.invalid (Paul Rubin)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Tue, 17 Jan 2023 11:31:13 -0800
Organization: A noiseless patient Spider
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 by: Paul Rubin - Tue, 17 Jan 2023 19:31 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> Anyone know of such a box? The programming might be contracted out,
> if you are interested. There's a prototype using an Arduino nano, but
> some of them are flaky and it would not hurt to start over from
> scratch.

There's about a gazillion industrial computers that do this, though they
are probably overkill and more expensive than one would prefer. This
one is on the front page of cnx-software right now:

https://www.cnx-software.com/2023/01/17/edatec-cm4-sensing-industrial-computer-offers-can-bus-rs485-and-rs232-interfaces/

Note that most of the boxed computers on that blog are quite powerful,
more than you need for this:

https://www.cnx-software.com/news/industrial

You could try a more general web search for "industrial embedded
computer" if that is the sort of thing you want. Do you need the box to
come from a real manufacturer with customer support? Is the idea to
deploy a moderate number of these, say dozens? A much larger number?
Or is it basically a one-off?

If characters are coming in at the full speed of the 9600 bps port, and
going out at the same speed, and more characters are going out than
coming in (because of the headers being added), how is this supposed to
work with no flow control?

Regarding the programming, if it is just as you describe, there is not
much to it, I would have thought.

If there is only one input port to this box, why use a box at all,
rather than have the sensor emit the header every 20 lines?

Re: Boxed MCU with RS-232 Port

<af677448-3930-4c1f-b6da-afdba5720305n@googlegroups.com>

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Tue, 17 Jan 2023 20:19 UTC

On Tuesday, January 17, 2023 at 3:31:21 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > Anyone know of such a box? The programming might be contracted out,
> > if you are interested. There's a prototype using an Arduino nano, but
> > some of them are flaky and it would not hurt to start over from
> > scratch.
> There's about a gazillion industrial computers that do this, though they
> are probably overkill and more expensive than one would prefer. This
> one is on the front page of cnx-software right now:
>
> https://www.cnx-software.com/2023/01/17/edatec-cm4-sensing-industrial-computer-offers-can-bus-rs485-and-rs232-interfaces/
>
> Note that most of the boxed computers on that blog are quite powerful,
> more than you need for this:
>
> https://www.cnx-software.com/news/industrial

Yes, way overkill. I think I said the initial units use the Arduino nano. No OS required, and in fact is a liability.

> You could try a more general web search for "industrial embedded
> computer" if that is the sort of thing you want.

Yes, and I get the sort of things you link to above.

> Do you need the box to
> come from a real manufacturer with customer support? Is the idea to
> deploy a moderate number of these, say dozens? A much larger number?
> Or is it basically a one-off?

I think they have built a dozen now. They expect to build a few more before the modify the receiver of the data to handle this function. They are making this with an Arduino nano and a small custom board for the RS-232 converter, in a 3d printed box. All of that is fine I expect. But they are having this problem.

Here's what I would like to use.
https://www.brainboxes.com/product/usb-to-serial/usb/us-257
https://www.brainboxes.com/product/ethernet-to-serial/db9/es-257
Right size, right case. But they are not a computer as such, they're USB or Ethernet based serial port adapters. I've written to them to see if this unit can be programmed by the user.

> If characters are coming in at the full speed of the 9600 bps port, and
> going out at the same speed, and more characters are going out than
> coming in (because of the headers being added), how is this supposed to
> work with no flow control?

You mean, how would it work *with* flow control, right? The data is coming in, 9,600 bps, 50 chars per second. There is a ton of idle time to send the headers between the 50 char messages.

> Regarding the programming, if it is just as you describe, there is not
> much to it, I would have thought.

There's always more than meets the eye. I looked at the code and although it's Arduino code, it is enough like C that I can tell it's missing a few things. One is, the files I have are line delimited by the DOS convention, /r/n. The program counts lines by checking for /r, ignoring /n. I don't know if that would cause any problems, but if the /r is missed from data corruption, the character buffer would likely overflow, causing who knows what harm. The character count should be checked for bounds. I'm not even sure why the data is being buffered, it could be sent through one character at a time, simply monitoring for the end of line.

> If there is only one input port to this box, why use a box at all,
> rather than have the sensor emit the header every 20 lines?

We don't control the sensor. It used to send a periodic header. They changed to a new model or an upgrade, or something else which means the header is no longer sent.

If I wasn't up to my ears, I would take this on. But I am, so I can't. But that may change.

Thanks for your reply.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

<87cz7cvpi0.fsf@nightsong.com>

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Subject: Re: Boxed MCU with RS-232 Port
Date: Tue, 17 Jan 2023 13:07:51 -0800
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 by: Paul Rubin - Tue, 17 Jan 2023 21:07 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> Yes, way overkill. I think I said the initial units use the Arduino
> nano. No OS required, and in fact is a liability.

The OS won't hurt, but maybe it won't help much if the thing is this
simple. I can say I worked on a much fancier gadget like this using an
ARM Linux board (it intercepted and modified the data stream between a
POS terminal and a receipt printer, doing full duplex comms on both
sides while also getting data from the internet) and it worked fine
using the on-board 16550-style UARTs.

> They are making this with an Arduino nano and a small custom board for
> the RS-232 converter, in a 3d printed box. All of that is fine I
> expect. But they are having this problem.

Hmm, I wonder if it can be diagnosed, if they are ok keeping on using
the same hardware. Any idea what was going wrong? Flaky hardware?
Underpowered RS232 ports?

> Here's what I would like to use.
> https://www.brainboxes.com/product/usb-to-serial/usb/us-257

Those look nice. I will keep looking around / asking around.

> There is a ton of idle time to send the headers between the 50 char
> messages.

Ah right, I had missed or forgotten that there was just one message per
second. Yes, you are fine.

> There's always more than meets the eye. I looked at the code and
> although it's Arduino code, it is enough like C that I can tell it's
> missing a few things.

Arduino code is C++ with some special libraries and light preprocessing,
so it shouldn't be too big a deal to hack it.

> I don't know if that would cause any problems, but if the /r is missed
> from data corruption, the character buffer would likely overflow,
> causing who knows what harm....

Fair enough, yes, the program should check for various kinds of errors.

Is it disastrous if an error results in some kind of alert that
temporarily stops operation? The idea is to deploy something that
passes reasonable testing, possibly hit a few unexpected error
conditions during initial production, fix those, and hopefully be
reliable afterwards, but have it not be catastrophic if something goes
wrong after a long period.

What do you want to have happen in case of data corruption anyway? Do
the messages have checksums and should the pass-through box check them?

> I'm not even sure why the data is being buffered, it could be sent
> through one character at a time...

If this thing is susceptible to later feature creep, the buffering might
make things easier.

It seems to me that if you have another person involved with the
programming, that person should be close to the customer site in order
to diagnose issues that might come up with the installed systems. Or at
least, they should have real sensor hardware that they can test with.

> If I wasn't up to my ears, I would take this on. But I am, so I
> can't.

Understandable ;).

Re: Boxed MCU with RS-232 Port

<2b3941b6-1a59-412c-b088-29794ac047b3n@googlegroups.com>

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Tue, 17 Jan 2023 21:29 UTC

On Tuesday, January 17, 2023 at 5:08:01 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > Yes, way overkill. I think I said the initial units use the Arduino
> > nano. No OS required, and in fact is a liability.
> The OS won't hurt, but maybe it won't help much if the thing is this
> simple. I can say I worked on a much fancier gadget like this using an
> ARM Linux board (it intercepted and modified the data stream between a
> POS terminal and a receipt printer, doing full duplex comms on both
> sides while also getting data from the internet) and it worked fine
> using the on-board 16550-style UARTs.
> > They are making this with an Arduino nano and a small custom board for
> > the RS-232 converter, in a 3d printed box. All of that is fine I
> > expect. But they are having this problem.
> Hmm, I wonder if it can be diagnosed, if they are ok keeping on using
> the same hardware. Any idea what was going wrong? Flaky hardware?
> Underpowered RS232 ports?

I don't know. The original guy who designed this is a bit busy. Because the problem is associated with some specific units, it's not terribly likely to be a coding issue. But who knows? Once the error is observed, a power cycle is required to fix it. It's not a one time glitch.

> > Here's what I would like to use.
> > https://www.brainboxes.com/product/usb-to-serial/usb/us-257
> Those look nice. I will keep looking around / asking around.
> > There is a ton of idle time to send the headers between the 50 char
> > messages.
> Ah right, I had missed or forgotten that there was just one message per
> second. Yes, you are fine.
> > There's always more than meets the eye. I looked at the code and
> > although it's Arduino code, it is enough like C that I can tell it's
> > missing a few things.
> Arduino code is C++ with some special libraries and light preprocessing,
> so it shouldn't be too big a deal to hack it.
> > I don't know if that would cause any problems, but if the /r is missed
> > from data corruption, the character buffer would likely overflow,
> > causing who knows what harm....
>
> Fair enough, yes, the program should check for various kinds of errors.
>
> Is it disastrous if an error results in some kind of alert that
> temporarily stops operation? The idea is to deploy something that
> passes reasonable testing, possibly hit a few unexpected error
> conditions during initial production, fix those, and hopefully be
> reliable afterwards, but have it not be catastrophic if something goes
> wrong after a long period.

This is actually a patch added when the sensor was changed to an updated model which no longer outputs the same format or the headers. It is likely to be dealt with by a change in the device that receives the reformatted data... at some point.

> What do you want to have happen in case of data corruption anyway? Do
> the messages have checksums and should the pass-through box check them?

I don't know. I think Checksums are overkill and just not appropriate. There's no one to add or check the checksums. I believe this is data that is simply being logged. The real problem is not the glitch, but that the failure remains until the translator is reset.

> > I'm not even sure why the data is being buffered, it could be sent
> > through one character at a time...
>
> If this thing is susceptible to later feature creep, the buffering might
> make things easier.

In talking to someone else, I remembered that the date and time formats are changed as well, so that's why the message is buffered.

> It seems to me that if you have another person involved with the
> programming, that person should be close to the customer site in order
> to diagnose issues that might come up with the installed systems. Or at
> least, they should have real sensor hardware that they can test with.

The problem follows certain units. I don't know how they did testing, but the units that work, work.

> > If I wasn't up to my ears, I would take this on. But I am, so I
> > can't.
> Understandable ;).

Anyone else have taller ears? lol

I'd be happy with a solid CPU in a good box. The current units are hand wired, so who knows how well they are made? This is the problem when one person designs something, then another person has to make it work. You never know where the bodies are buried.

Thanks for your insights.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
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 by: Paul Rubin - Tue, 17 Jan 2023 22:04 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> Once the error is observed, a power cycle is required to fix it. It's
> not a one time glitch.

Gack, yeah. I had been thinking, this isn't my area, but my
understanding is that the RS232 electrical spec requires voltages that
are somewhat above TTL logic levels, and that various crappy devices
skimp on these voltages and mostly work anyway. So that is a thing to
suspect if a home-brew RS232 device is acting flaky. It could be that
the device at the other end expects those voltages to be closer to the
real spec.

> This is actually a patch added when the sensor was changed to an
> updated model which no longer outputs the same format or the headers.

Can I ask about the device or computer that is receiving this data?
Does that have software of its own that can be modified? Adding a
hardware box just to deal with a software protocol change seems pretty
desperate.

> The real problem is not the glitch, but that the failure remains until
> the translator is reset.

How about including a WDT that resets the circuit? Is it possible to
tell if the CPU is even still running when the device locks up?

> I'd be happy with a solid CPU in a good box. The current units are
> hand wired, so who knows how well they are made?

As a test, you could put in a laptop with an FTDI cable and see if that
is able to keep the system happy. That's how we tested all our stuff
with the POS interception thing that I mentioned.

> This is the problem when one person designs something, then another
> person has to make it work. You never know where the bodies are
> buried.

Yes, that's why getting a remote contractor involved for something this
simple sounds like more trouble than it's worth. It's much more hassle
than if the person is already there in your shop and is familiar with
the product.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Tue, 17 Jan 2023 22:47 UTC

On Tuesday, January 17, 2023 at 6:04:44 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > Once the error is observed, a power cycle is required to fix it. It's
> > not a one time glitch.
> Gack, yeah. I had been thinking, this isn't my area, but my
> understanding is that the RS232 electrical spec requires voltages that
> are somewhat above TTL logic levels, and that various crappy devices
> skimp on these voltages and mostly work anyway. So that is a thing to
> suspect if a home-brew RS232 device is acting flaky. It could be that
> the device at the other end expects those voltages to be closer to the
> real spec.

They used a MAX3232CPE which generates it's own voltages using switched capacitor voltage boost. I wanted to check the values of the caps. Seems the have different minimum values depending on the Vcc voltage. But they are not in the BoM. I'll ask about this. It could easily be the cause of the problem.

> > This is actually a patch added when the sensor was changed to an
> > updated model which no longer outputs the same format or the headers.
> Can I ask about the device or computer that is receiving this data?
> Does that have software of its own that can be modified? Adding a
> hardware box just to deal with a software protocol change seems pretty
> desperate.

"Desparate"? They just don't want to mess with the box that is receiving the data, not yet anyway. This was supposed to be an easy way to get it working with a minimum of fuss. It just didn't work out.

> > The real problem is not the glitch, but that the failure remains until
> > the translator is reset.
> How about including a WDT that resets the circuit? Is it possible to
> tell if the CPU is even still running when the device locks up?
> > I'd be happy with a solid CPU in a good box. The current units are
> > hand wired, so who knows how well they are made?
> As a test, you could put in a laptop with an FTDI cable and see if that
> is able to keep the system happy. That's how we tested all our stuff
> with the POS interception thing that I mentioned.

We have units that work. We have units that fail. I don't know what we would learn from using a laptop.

> > This is the problem when one person designs something, then another
> > person has to make it work. You never know where the bodies are
> > buried.
> Yes, that's why getting a remote contractor involved for something this
> simple sounds like more trouble than it's worth. It's much more hassle
> than if the person is already there in your shop and is familiar with
> the product.

If pigs had wings, they would fly. The only trouble is, they don't have wings.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
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 by: Paul Rubin - Tue, 17 Jan 2023 23:32 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> "Desparate"? They just don't want to mess with the box that is
> receiving the data, not yet anyway.

Well, desperate in the sense that modifying software is usually easier
than deploying and maintaining another physical computer, but I guess it
depends on how hard it is to mess with that box.

> We have units that work. We have units that fail. I don't know what
> we would learn from using a laptop.

If the laptop worked reliably it would show that the basic FTDI
interface was sufficient. It would also allow spotting issues with the
incoming data, etc.

Someone on irc suggested using thin clients from ebay:

https://www.ebay.com/itm/125720309804

They are cheap and plentiful, but maybe not the right look, as it were.

> If pigs had wings, they would fly. The only trouble is, they don't
> have wings.

I just worry that if this is all special purpose hardware at the
endpoints, making the gizmo work may involve checking levels with an
oscilloscope and stuff like that, rather than being a pure software
matter. The laptop could help test that theory.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Tue, 17 Jan 2023 23:44 UTC

On Tuesday, January 17, 2023 at 7:32:51 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > "Desparate"? They just don't want to mess with the box that is
> > receiving the data, not yet anyway.
> Well, desperate in the sense that modifying software is usually easier
> than deploying and maintaining another physical computer, but I guess it
> depends on how hard it is to mess with that box.
> > We have units that work. We have units that fail. I don't know what
> > we would learn from using a laptop.
> If the laptop worked reliably it would show that the basic FTDI
> interface was sufficient. It would also allow spotting issues with the
> incoming data, etc.

??? You seem to be missing the fact that there are existing units that do the job without a problem. The problem is linked to specific units. There's nothing to learn from using a laptop. I believe they have used a PC running Putty to capture data on the serial ports.

You are looking where the light is better, in spite of the fact we know the problems not there.

> Someone on irc suggested using thin clients from ebay:
>
> https://www.ebay.com/itm/125720309804
>
> They are cheap and plentiful, but maybe not the right look, as it were.
> > If pigs had wings, they would fly. The only trouble is, they don't
> > have wings.
> I just worry that if this is all special purpose hardware at the
> endpoints, making the gizmo work may involve checking levels with an
> oscilloscope and stuff like that, rather than being a pure software
> matter. The laptop could help test that theory.

You mean a laptop with an oscilloscope dongle? A digital measurement of the RS232 signals by a PC is not of much use if you don't know where the thresholds are.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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 by: Paul Rubin - Wed, 18 Jan 2023 00:04 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> There's nothing to learn from using a laptop. I believe they
> have used a PC running Putty to capture data on the serial ports.

Ok, same idea.

> You mean a laptop with an oscilloscope dongle?

I mean an scope with analog inputs to check voltages, timings, noise,
etc. You have boxes that work and boxes that mostly work. What makes
the boxes different from one another? It sounds like something
somewhere is marginal.

I hope this extreme an approach is not needed, but if custom hardware is
involved and you have the final responsibility of getting everything
working, you have to be ready for whatever it might take.

I remember on the POS project, we had some kind of multi-channel logic
analyzer for this purpose, though I don't remember using it. We also
had some hacked up serial cables that let us monitor the traffic between
two devices by tapping the TX and RX pins and bringing them out to a
third DB9 plug that we connected to another computer. Those cables were
very useful. I think I can figure out how they worked, but I've been
wanting to ask the guy who built them, just to be sure.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Wed, 18 Jan 2023 01:32 UTC

On Tuesday, January 17, 2023 at 8:04:10 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > There's nothing to learn from using a laptop. I believe they
> > have used a PC running Putty to capture data on the serial ports.
> Ok, same idea.
> > You mean a laptop with an oscilloscope dongle?
> I mean an scope with analog inputs to check voltages, timings, noise,
> etc. You have boxes that work and boxes that mostly work. What makes
> the boxes different from one another? It sounds like something
> somewhere is marginal.

If you know anything about RS-232, you would know that it has margin on top of margin preventing marginal issues. The spec is that the voltages between +3V and -3V at the input of the receiver, while the driver is specified to drive at least ±5V. There's 2V margin. Then there's the fact that the actual threshold of the receiver is around 0.7V. I measured this once, but I don't recall the exact number, it might be more like 1.0V. The point is, there's another 2V margin.

I've asked for the values of the caps on the MAX3232 chip. If one of those is out of spec, it could impact the drive capability.

I don't have the units, so I can't put a scope on anything.

> I hope this extreme an approach is not needed, but if custom hardware is
> involved and you have the final responsibility of getting everything
> working, you have to be ready for whatever it might take.
>
> I remember on the POS project, we had some kind of multi-channel logic
> analyzer for this purpose, though I don't remember using it. We also
> had some hacked up serial cables that let us monitor the traffic between
> two devices by tapping the TX and RX pins and bringing them out to a
> third DB9 plug that we connected to another computer. Those cables were
> very useful. I think I can figure out how they worked, but I've been
> wanting to ask the guy who built them, just to be sure.

Not sure how a logic analyzer would help. That's for digital signals. You are talking about an analog issue.

I would like to find some hardware appropriate to the task. I can't even find an Arduino compatible board that has an RS-232 level shifter chip on the board. Everyone just copies the same design. I also can't find any lower end MCU in an enclosure with two serial ports. Everything I've found is a hulking x86 compatible gadget with all sorts of high end interfaces, and only one serial port if any. I guess that's why the guy made his own box. But there are tons of RS-232 interface boards to use with the Arduino. I guess the fact that they have the DB-9 connector is a problem.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
Date: Tue, 17 Jan 2023 20:02:12 -0800
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 by: Paul Rubin - Wed, 18 Jan 2023 04:02 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> Not sure how a logic analyzer would help. That's for digital signals.
> You are talking about an analog issue.

The logic analyzer for the POS thing was probably for debugging timing
problems. I think it was able to timestamp more accurately than our
software hack could. You are right that it wouldn't handle analog
issues.

> Everything I've found is a hulking x86 compatible gadget with all
> sorts of high end interfaces, and only one serial port if any.

There's a number of ARM boards with RS232 but that's just x86 in
minuature, perhaps. Here is one with two RS232's, and again way more
other stuff than you want:

https://www.olimex.com/Products/ARM/NXP/LPC2378-STK/

Actually it looks like they have (had?) an AVR board with RS232 (single
port, meh). It is out of stock though, and (who knows) maybe
discontinued:

https://www.olimex.com/Products/AVR/Development/AVR-CAN/

Were you thinking of using a single port and splitting out the TX and RX
wires? That is a little bit too hacky imho.

The company is in Bulgaria but some of their stuff is stocked by
Digikey, so you could check there.

Also maybe this?

https://microcontrollershop.com/product_info.php?products_id=3517

Claims to have two uart ports and rs232 tranceiver chip, but uses
JST-like connectors rather than DB9. Same processor as the generic ARM
Bluepill though, and no extra ports other than USB.

Hmm, this one has two DB9's:

https://microcontrollershop.com/product_info.php?products_id=743

Anyway you can find other stuff there too.

> But there are tons of RS-232 interface boards to use with the Arduino.
> I guess the fact that they have the DB-9 connector is a problem.

I think stuff these days tends to use USB, which is its own can of
worms, but it is easy to get USB to serial converter cables.

There is this though, 1 port:

https://microcontrollershop.com/product_info.php?products_id=5579

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Wed, 18 Jan 2023 04:24 UTC

On Wednesday, January 18, 2023 at 12:02:22 AM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > Not sure how a logic analyzer would help. That's for digital signals.
> > You are talking about an analog issue.
> The logic analyzer for the POS thing was probably for debugging timing
> problems. I think it was able to timestamp more accurately than our
> software hack could. You are right that it wouldn't handle analog
> issues.
> > Everything I've found is a hulking x86 compatible gadget with all
> > sorts of high end interfaces, and only one serial port if any.
> There's a number of ARM boards with RS232 but that's just x86 in
> minuature, perhaps. Here is one with two RS232's, and again way more
> other stuff than you want:
>
> https://www.olimex.com/Products/ARM/NXP/LPC2378-STK/
>
> Actually it looks like they have (had?) an AVR board with RS232 (single
> port, meh). It is out of stock though, and (who knows) maybe
> discontinued:
>
> https://www.olimex.com/Products/AVR/Development/AVR-CAN/
>
> Were you thinking of using a single port and splitting out the TX and RX
> wires? That is a little bit too hacky imho.
>
> The company is in Bulgaria but some of their stuff is stocked by
> Digikey, so you could check there.
>
> Also maybe this?
>
> https://microcontrollershop.com/product_info.php?products_id=3517
>
> Claims to have two uart ports and rs232 tranceiver chip, but uses
> JST-like connectors rather than DB9. Same processor as the generic ARM
> Bluepill though, and no extra ports other than USB.
>
> Hmm, this one has two DB9's:
>
> https://microcontrollershop.com/product_info.php?products_id=743
>
> Anyway you can find other stuff there too.
> > But there are tons of RS-232 interface boards to use with the Arduino.
> > I guess the fact that they have the DB-9 connector is a problem.
> I think stuff these days tends to use USB, which is its own can of
> worms, but it is easy to get USB to serial converter cables.
>
> There is this though, 1 port:
>
> https://microcontrollershop.com/product_info.php?products_id=5579

I guess I'm getting tired. If I'm buying a board, one serial port is fine. UARTs are two separate devices, a transmitter and a receiver. They are not connected other than sharing the same bit rate and other format configuration, perhaps. The only reason for wanting two serial ports would be when buying a box level product, since external wiring is simpler with two cables, rather than a Y cable

ARM boards would be fine, but I'm not making a box, so I guess this will be someone else's problem.

I'm very surprised Digikey and Mouser don't carry a box device like this. They have lots of embedded computers, but they are like a PC in a small case. Some are like rPi's, with ARM processors, but still too messy dealing with a complex processor and an OS.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
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 by: Paul Rubin - Wed, 18 Jan 2023 04:56 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> I'm very surprised Digikey and Mouser don't carry a box device like
> this.

It is weird, there must be something like that, but product search
everywhere is terrible. I notice there is a new stackexchange for
hardware recommendations:

https://hardwarerecs.stackexchange.com/

It doesn't look that great, but who knows.

> Some are like rPi's, with ARM processors, but still too messy dealing
> with a complex processor and an OS.

If you can power it up and get a linux shell and run gcc, that is pretty
easy to deal with. You don't have to worry about the amount of software
underneath the shell prompt, you don't have to worry about UART device
registers since the OS handles that, etc. I do understand that it is
hardware overkill despite this.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Wed, 18 Jan 2023 06:30 UTC

On Wednesday, January 18, 2023 at 12:56:13 AM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > I'm very surprised Digikey and Mouser don't carry a box device like
> > this.
> It is weird, there must be something like that, but product search
> everywhere is terrible. I notice there is a new stackexchange for
> hardware recommendations:
>
> https://hardwarerecs.stackexchange.com/

Ok, I've posted there. Thanks.

> It doesn't look that great, but who knows.
> > Some are like rPi's, with ARM processors, but still too messy dealing
> > with a complex processor and an OS.
> If you can power it up and get a linux shell and run gcc, that is pretty
> easy to deal with.

That's not really true. One way of making an MCU robust, is to reboot it periodically. If it can reboot in less than a second, it can do this job while invisibly rebooting. It takes significant time to reboot an rPi. There's ZERO reason to bother with more complex hardware that still doesn't have RS-232 I/Os or a case.

> You don't have to worry about the amount of software
> underneath the shell prompt, you don't have to worry about UART device
> registers since the OS handles that, etc. I do understand that it is
> hardware overkill despite this.

No, no reason to worry about any of that, because an OS is not going to be in the device.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
Date: Wed, 18 Jan 2023 00:37:04 -0800
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 by: Paul Rubin - Wed, 18 Jan 2023 08:37 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> That's not really true. One way of making an MCU robust, is to reboot
> it periodically. If it can reboot in less than a second, it can do
> this job while invisibly rebooting. It takes significant time to
> reboot an rPi.

So have it auto-reboot at night. More seriously, the thing that fails
the most on Rpi-style boards is the SD card. If you have a board that
doesn't use an SD card, it can be pretty robust.

> No, no reason to worry about any of that, because an OS is not going
> to be in the device.

Of course the Arduino library is sort of an OS, if you use it.

I still worry a little about whatever is making your existing box fail.
If you can isolate it to those capacitors or whatever it was, that is
great. Otherwise maybe you have to be ready for the possibility of
installing a ready-made box with properly working RS232 ports and still
finding that it occasionally fails the same way.

Regarding the boxed microcomputer, someone on the Forth group might know
of a suitable product? It's the type of thing they might be using.

Re: Boxed MCU with RS-232 Port

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From: david.br...@hesbynett.no (David Brown)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Wed, 18 Jan 2023 10:04:30 +0100
Organization: A noiseless patient Spider
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 by: David Brown - Wed, 18 Jan 2023 09:04 UTC

On 17/01/2023 21:19, Rick C wrote:

> There's always more than meets the eye. I looked at the code and
> although it's Arduino code, it is enough like C that I can tell it's
> missing a few things. One is, the files I have are line delimited by
> the DOS convention, /r/n. The program counts lines by checking for
> /r, ignoring /n. I don't know if that would cause any problems, but
> if the /r is missed from data corruption, the character buffer would
> likely overflow, causing who knows what harm. The character count
> should be checked for bounds. I'm not even sure why the data is
> being buffered, it could be sent through one character at a time,
> simply monitoring for the end of line.

You mean "\r" and "\n" here - programming is fussy about the details!

When counting line endings, I usually accept either character, and if
"\r" is received then a following "\n" is ignored (and vice versa - some
people get things wrong and send "\n\r").

The standard for DOS is "\r\n", the standard for *nix is "\n", and the
standard for old Macs is "\r". I would not be happy simply counting
"\r" characters unless I was sure the incoming data always used carriage
returns - if I were to pick just one character, it would be "\n". But
checking for either is best.

Data corruption is always something you have to consider. Sometimes you
can't do much about it, and will just pass on the mess - or skip it
until the data looks good again. But you at least want to make sure
there are no buffer overflows if a line ending is missed!

Re: Boxed MCU with RS-232 Port

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From: andr...@sdf.org (Andrew Smallshaw)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Wed, 18 Jan 2023 12:15:55 -0000 (UTC)
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 by: Andrew Smallshaw - Wed, 18 Jan 2023 12:15 UTC

On 2023-01-17, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
> On Tuesday, January 17, 2023 at 6:04:44 PM UTC-4, Paul Rubin wrote:
>> Gack, yeah. I had been thinking, this isn't my area, but my
>> understanding is that the RS232 electrical spec requires voltages that
>> are somewhat above TTL logic levels, and that various crappy devices
>> skimp on these voltages and mostly work anyway. So that is a thing to
>> suspect if a home-brew RS232 device is acting flaky. It could be that
>> the device at the other end expects those voltages to be closer to the
>> real spec.
>
> They used a MAX3232CPE which generates it's own voltages using
> switched capacitor voltage boost. I wanted to check the values of
> the caps. Seems the have different minimum values depending on
> the Vcc voltage. But they are not in the BoM. I'll ask about
> this. It could easily be the cause of the problem.

That was my first thought as well so I looked it up to double check.
The MAX3232CPE is 0.1uF across the board so far as I can see. You
do hit problems with MAX232's - the original needed 1uF caps but
the MAX232A and several alternate manufacturers specify 0.1uF as
a minimum. Problems can arise if a MAX232 is put in place of one
of the alternatives but with the 3232 I'd expect people to get it
right.

OTOH the 3232 is a 3.3V compatible part. One thing they all have
in common is the charge pumps are a bit weedy in terms of voltage,
aiming for +/-5.5V regardless of supply voltage. That's within
current specs but the RS232 minimum voltages have dropped over the
years, I suppose it's possible the port of the receiver is an
older design. In any case it doesn't leave particularly large
headroom for losses. Do you know if the protocol translator is on
a 3.3v or 5v supply? If the latter a MAX232A (note the A) is a
drop-in replacement with typical +/-10V drive. If 3.3V a booster
of some form will eliminate low voltage as an issue - in terms of
off the shelf hardware that would probably be a pair of RS232<>RS422
line extenders back to back.

--
Andrew Smallshaw
andrews@sdf.org

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Wed, 18 Jan 2023 12:43 UTC

On Wednesday, January 18, 2023 at 4:37:13 AM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > That's not really true. One way of making an MCU robust, is to reboot
> > it periodically. If it can reboot in less than a second, it can do
> > this job while invisibly rebooting. It takes significant time to
> > reboot an rPi.
> So have it auto-reboot at night. More seriously, the thing that fails
> the most on Rpi-style boards is the SD card. If you have a board that
> doesn't use an SD card, it can be pretty robust.

So potentially lose an entire day of data? LOL

> > No, no reason to worry about any of that, because an OS is not going
> > to be in the device.
> Of course the Arduino library is sort of an OS, if you use it.

Now this is getting silly.

> I still worry a little about whatever is making your existing box fail.
> If you can isolate it to those capacitors or whatever it was, that is
> great. Otherwise maybe you have to be ready for the possibility of
> installing a ready-made box with properly working RS232 ports and still
> finding that it occasionally fails the same way.

Yes, and I would still need to worry about it being stepped on by a dinosaur.

> Regarding the boxed microcomputer, someone on the Forth group might know
> of a suitable product? It's the type of thing they might be using.

Maybe.

--

Rick C.

-+- Get 1,000 miles of free Supercharging
-+- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Wed, 18 Jan 2023 12:55 UTC

On Wednesday, January 18, 2023 at 8:16:01 AM UTC-4, Andrew Smallshaw wrote:
> On 2023-01-17, Rick C <gnuarm.del...@gmail.com> wrote:
> > On Tuesday, January 17, 2023 at 6:04:44 PM UTC-4, Paul Rubin wrote:
> >> Gack, yeah. I had been thinking, this isn't my area, but my
> >> understanding is that the RS232 electrical spec requires voltages that
> >> are somewhat above TTL logic levels, and that various crappy devices
> >> skimp on these voltages and mostly work anyway. So that is a thing to
> >> suspect if a home-brew RS232 device is acting flaky. It could be that
> >> the device at the other end expects those voltages to be closer to the
> >> real spec.
> >
> > They used a MAX3232CPE which generates it's own voltages using
> > switched capacitor voltage boost. I wanted to check the values of
> > the caps. Seems the have different minimum values depending on
> > the Vcc voltage. But they are not in the BoM. I'll ask about
> > this. It could easily be the cause of the problem.
> That was my first thought as well so I looked it up to double check.
> The MAX3232CPE is 0.1uF across the board so far as I can see. You
> do hit problems with MAX232's - the original needed 1uF caps but
> the MAX232A and several alternate manufacturers specify 0.1uF as
> a minimum. Problems can arise if a MAX232 is put in place of one
> of the alternatives but with the 3232 I'd expect people to get it
> right.

The data sheet I saw has a table of minimum capacitance for three Vcc ranges, 3.3V, 5V and 3.3 to 5V approximately. Only 3.3V was 0.1 uF on all caps. The others were larger on at least one cap. Table 9-1 on page 12.

> OTOH the 3232 is a 3.3V compatible part. One thing they all have
> in common is the charge pumps are a bit weedy in terms of voltage,
> aiming for +/-5.5V regardless of supply voltage. That's within
> current specs but the RS232 minimum voltages have dropped over the
> years, I suppose it's possible the port of the receiver is an
> older design.

You mean the RS-232 (TIA/EIAI) specification has changed? I have not seen this.

> In any case it doesn't leave particularly large
> headroom for losses. Do you know if the protocol translator is on
> a 3.3v or 5v supply? If the latter a MAX232A (note the A) is a
> drop-in replacement with typical +/-10V drive. If 3.3V a booster
> of some form will eliminate low voltage as an issue - in terms of
> off the shelf hardware that would probably be a pair of RS232<>RS422
> line extenders back to back.

5V supply. I don't know why you are talking about the MAX232. I've said "MAX3232CPE" several times.

--

Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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From: andr...@sdf.org (Andrew Smallshaw)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Wed, 18 Jan 2023 13:22:15 -0000 (UTC)
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 by: Andrew Smallshaw - Wed, 18 Jan 2023 13:22 UTC

On 2023-01-18, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
>
> The data sheet I saw has a table of minimum capacitance for three
> Vcc ranges, 3.3V, 5V and 3.3 to 5V approximately. Only 3.3V was
> 0.1 uF on all caps. The others were larger on at least one cap.
> Table 9-1 on page 12. 1

I'm reading Maxim's datasheet, see
https://pdf1.alldatasheet.com/datasheet-pdf/view/73152/MAXIM/MAX3232CPE.html
If you're looking at a sheet from another manufacturer that may
change, leading to the same kind of incompatibility as seen with
the MAX232 variants.

> You mean the RS-232 (TIA/EIAI) specification has changed? I have
> not seen this.

Not recently but over time, yes. From memory the initial spec was
+/-12V. I think it was RS232C that lowered it to +/-9V but don't
hold me to that. It was either RS232E or F that lowered it again
to +/-5V. Even the 'F' revision is fairly old now, but 'C' got so
deeply ingrained it's not unusual to see references to RS232C even
today. All specify inputs must tolerate up to +/-25V so there is
cross-compatibility in terms of avoiding damage at least, but RS232
is one of those standards that often doesn't get implemented rigidly,
e.g. power thieves, discrete implementations that are not strictly
compliant, and so on.

> 5V supply. I don't know why you are talking about the MAX232.
> I've said "MAX3232CPE" several times.

Acknowledged. MAX232 is the classic part for this application and
where I suspect most people will have gained their initial experience.
It's the one that has the most issue with the cap sizing. It's
also a 5V only part. The MAX2323 is a 3.3V/5V part, at 5V it's
interchangable with the MAX232 but the latter has higher output
levels. If thresholds are the marginal factor here that's why I
suggest it as a possible experiment.

--
Andrew Smallshaw
andrews@sdf.org

Re: Boxed MCU with RS-232 Port

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From: andr...@sdf.org (Andrew Smallshaw)
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Subject: Re: Boxed MCU with RS-232 Port
Date: Wed, 18 Jan 2023 13:28:10 -0000 (UTC)
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 by: Andrew Smallshaw - Wed, 18 Jan 2023 13:28 UTC

On 2023-01-18, Andrew Smallshaw <andrews@sdf.org> wrote:
>
> Acknowledged. MAX232 is the classic part for this application and
> where I suspect most people will have gained their initial experience.
> It's the one that has the most issue with the cap sizing. It's
> also a 5V only part. The MAX2323 is a 3.3V/5V part, at 5V it's
> interchangable with the MAX232 but the latter has higher output
> levels. If thresholds are the marginal factor here that's why I
> suggest it as a possible experiment.

Sorry, to emphasise again, a MAX232_A_ can be substituted. A
genuine Maxim MAX232 needs larger caps.

--
Andrew Smallshaw
andrews@sdf.org

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Wed, 18 Jan 2023 14:20 UTC

On Wednesday, January 18, 2023 at 9:22:20 AM UTC-4, Andrew Smallshaw wrote:
> On 2023-01-18, Rick C <gnuarm.del...@gmail.com> wrote:
> >
> > The data sheet I saw has a table of minimum capacitance for three
> > Vcc ranges, 3.3V, 5V and 3.3 to 5V approximately. Only 3.3V was
> > 0.1 uF on all caps. The others were larger on at least one cap.
> > Table 9-1 on page 12. 1
>
> I'm reading Maxim's datasheet, see
> https://pdf1.alldatasheet.com/datasheet-pdf/view/73152/MAXIM/MAX3232CPE.html
> If you're looking at a sheet from another manufacturer that may
> change, leading to the same kind of incompatibility as seen with
> the MAX232 variants.

Did you look at the data sheet you linked to? What are the minimum capacitor recommendations for the MAX3232?

> > You mean the RS-232 (TIA/EIAI) specification has changed? I have
> > not seen this.
> Not recently but over time, yes. From memory the initial spec was
> +/-12V. I think it was RS232C that lowered it to +/-9V but don't
> hold me to that. It was either RS232E or F that lowered it again
> to +/-5V. Even the 'F' revision is fairly old now, but 'C' got so
> deeply ingrained it's not unusual to see references to RS232C even
> today.

I think your memory is faulty. It has always been a minimum of ±5V at the driver output as long as I can recall. RS232C is from 1969. More recent changes were made to make the standard interworkable with ITU-T/CCITT V..24.

The receiver voltage requirement of ±3V allows for variation in the actual threshold of the receiver. The spec has also always allowed up to ±25V at the driver, unloaded, and an output resistance of 3 to 7 kohms. The difference between the output and input voltage ranges allows for at least 2V of noise on the line.

> All specify inputs must tolerate up to +/-25V so there is
> cross-compatibility in terms of avoiding damage at least, but RS232
> is one of those standards that often doesn't get implemented rigidly,
> e.g. power thieves, discrete implementations that are not strictly
> compliant, and so on.
> > 5V supply. I don't know why you are talking about the MAX232.
> > I've said "MAX3232CPE" several times.
> Acknowledged. MAX232 is the classic part for this application and
> where I suspect most people will have gained their initial experience.
> It's the one that has the most issue with the cap sizing. It's
> also a 5V only part. The MAX2323 is a 3.3V/5V part, at 5V it's
> interchangable with the MAX232 but the latter has higher output
> levels. If thresholds are the marginal factor here that's why I
> suggest it as a possible experiment.

If the voltage levels are marginal, that would best be discovered by using an oscilloscope to measure them as well as the rise/fall times and the pulse timings.

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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From: theom+n...@chiark.greenend.org.uk (Theo)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: 18 Jan 2023 16:18:05 +0000 (GMT)
Organization: University of Cambridge, England
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 by: Theo - Wed, 18 Jan 2023 16:18 UTC

Rick C <gnuarm.deletethisbit@gmail.com> wrote:
> Anyone know of such a box? The programming might be contracted out, if
> you are interested. There's a prototype using an Arduino nano, but some
> of them are flaky and it would not hurt to start over from scratch.

I was wondering about boxes that do MIDI, eg MIDI to USB conversion. MIDI
is just serial with a strange (31K) baud rate, and those boxes often have
multiple MIDI ports (although not as many UARTs as ports). The downside is
that MIDI is a current loop so the electrical signalling is wrong.

Also wondered if there are RS232-to-X boxes (eg USB) where the main chip is
an MCU that can be reprogrammed. But if you want two ports that's harder.

Another thought is to find a common 'gender changer' case, a plastic case
that would take a DB9 connector at each end, and drop in your own PCB. eg
https://uk.misumi-ec.com/vona2/detail/222301880534/#
- they have a DB9 to DB9 version:
https://uk.misumi-ec.com/pdf/vona/el/PVT1/PVT1_670909M_Datasheet_de_en_1.pdf
(this used to be a very common design but seems harder to find these days)

Theo

Re: Boxed MCU with RS-232 Port

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From: no.em...@nospam.invalid (Paul Rubin)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Wed, 18 Jan 2023 14:10:12 -0800
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 by: Paul Rubin - Wed, 18 Jan 2023 22:10 UTC

Theo <theom+news@chiark.greenend.org.uk> writes:
> Another thought is to find a common 'gender changer' case, a plastic case
> that would take a DB9 connector at each end, and drop in your own PCB. eg

I think the hope is to not build hardware at all, including dropping
boards into things, but instead to buy a complete and packaged box that
you can plug cables into. I'm surprised that it seems this difficult.
Maybe it is an opportunity.

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