Boxed MCU with RS-232 Port

Yes, but initially I was looking for something more like an Arduino in a box. That never materialized. The solution we are looking at now, is a custom design someone did for another project, that suits our needs, but since the production quantities are low, the unit price is a bit steep, even if manageable.

LOL! Aliexpress is literally the last place I would go for commercial gear.

Useless, since you may not be able to buy the same unit even six months from now.

But thanks for the suggestion. I'm presently talking to Aaeon who has some affordable units.

Reply to
Rick C
Loading thread data ...

That's one of the problems. Boards like Arduinos do not have RS-232 support. They have serial ports, but that's what was tried initially, with a home brew RS-232 level shifter added on a perf board. Don't know why, but half of them tend to hang, even if after days. Not acceptable.

Sounds great. Do you have a proposal?

Yeah, I'll just do the software myself. The cost difference between the Arduino and a minature PC is so small, it's more than made up in the savings of not having to do any of the stuff you mentioned other than write software.

Reply to
Rick C

Multiple. Some are in the DC area.

Reply to
Rick C

I thought I had located one and posted a link here. I'll look again.

I'm open to this but I'm probably not the best person for it, since I'm mostly a software guy. Do you have a timeframe? I can also check with other people I know who might be interested, and will refer them to you by email if they are.

Reply to
Paul Rubin

Color me puzzled. Why on earth would anyone home-brew an RS232 level shifter, particularly for a project that could clearly afford using ready-made ICs like MAX232 instead?

Reply to
Hans-Bernhard Bröker

The problem is that commercial microcontroller boards like Arduinos tend to have TTL level serial ports (or USB ones). If you want a box holding one of those with some RS232 ports, you need to make a PCB with a MAX232 and a DB9, and an enclosure to match. Rick was trying to find a box with all that already done for him and drew a blank.

It's not the design that's the problem, it's the manufacturing.

Although for quantity 20 at these kind of price points, I might be tempted to build something using dev boards, eg:

formatting link
maybe a bit of 3D printing for an enclosure. For two of those boards you might need to hand-patch one to use different pins, but it's not hard and could be done.

If the customer is willing to pay $300 a unit it might be worth Rick's (or somebody else's) time to do it. I'll be happy to take that contract, email address works :-)

Theo

Reply to
Theo

That's what they used. I simply meant it was not a commercial product on a PCB. Half the units have some problem.

Did you think I meant they designed their own level shifter chip?

Reply to
Rick C

This device is exactly what makes this difficult. Which pin on the DB9 is the data output?

You will need to post an email address. GG doesn't provide the email. Just snipped-for-privacy@t-online.de

Reply to
Rick C

A lot of power consumption for such a task! An Atmel board would only consume about 0.4 W, for example something like that:

formatting link
?products_id=35 The price is crazy, but there should be similar devices for only 1/5 of this price.

Reply to
Herbert Kleebauer

TXD (output of MAX2323ESE) is pin 2, RXD (input of MAX2323ESE) is pin 3.

ie would connect to a PC via a straight-through cable, not a null modem.

My email is on the bottom of

formatting link
(I am in the UK, if that makes a difference)

Theo

Reply to
Theo

The same company (ledato.de, taskit.de) has also an ARM board with Ubuntu and 2 (or 3) RS232 ports which is cheaper:

formatting link

Reply to
Herbert Kleebauer

You said you home-brewed the level shifter. How else was anybody to interpret that?

Reply to
Hans-Bernhard Bröker

Am 24.03.2023 um 15:20 schrieb Theo:

Of course he did. Finding that kind of box off-the-shelf was a very long shot, IMHO.

Industrialized versions of the Raspberry Pi might have come close, but they're more likely to offer RS485 or 422, insead of 232.

Reply to
Hans-Bernhard Bröker

There should be many things in this world.

Reply to
Rick C

The pinout is given here:

formatting link
How do you feel about using that board, with an Arduino? Digikey stocks it, if that helps:

formatting link
How do you feel about recycling the enclosure from one of those port selector switches discussed a while back?

Here is a Lilygo board which has an ESP32-C3 MCU and RS232 among other things, for $17.98:

formatting link
It is shipped from China so maybe doesn't fulfill requirements because of that, but it at least shows that such a product exists.

Article about it with an Aliexpress redirect link (it is also sold through there):

formatting link
Direct Aliexpress

formatting link
Here is an Olimex MSP430 board with RS232 for around $32:

formatting link
It is available at Mouser, though they only have 9 in stock right now:

formatting link
It is also on Digikey's site, but out of stock there.

There are more Olimex boards with RS232 that I didn't look up.

You mentioned that you didn't want to use an external FTDI cable on a USB port. What about having an FTDI dongle inside the box, installed so that its DB9 connector is panel mounted?

formatting link
TTL to RS232 (?):
formatting link
formatting link
Regarding the locations: are any in the western US?

Reply to
Paul Rubin

You didn't answer the question. Which pin is the data output and which is the data input?

Are you going to make the cable required?

Recycling is not a problem, as long as there is no branding on the box.

Are you going to write the USB stack to run on the simple CPUs you have linked to?

I don't know why you are showing all these devices.

I don't know. Why does this matter? You won't be visiting the customer's site.

You seem to be thrashing around in looking at every little board that might or might not do the job, rather than finding one that will. The single port boards you've identified have the DB9 connector, but you don't indicate how you will split this into the two connectors required for the job.

Do you understand the requirements?

Reply to
Rick C

The transmit pin (TXD, pin 2 in that table) is the output and the receive pin (RXD, pin 3) is the input. Since it is a female connector, by the standard, the box is considered data communications equipment (DCE), rather than data terminal equipment (DTR). If it was DTR, the two pins would be switched around. Is that what you are asking? In any case, one always has to test to be sure.

A splitter cable? I thought I posted a url to order those from.

There could be a label with your own branding, strategically placed to cover up any existing branding, if that works for you.

It exists already on some of them. I wouldn't write a new one.

There are tons of cpus with built in UARTs

Somebody at some point might have to do that. I hope not, but the saying is, hope for the best and plan for the worst.

Frankly the first thing I would try is taking one of your homebrew boxes that is known to be failing, swapping out the homemade level shifter PCB with one of the ones linked above, and seeing if that works. Or at least, use a scope to check the voltages coming out of the homemade PCB.

It is a two step process: 1) identify possible candidates; 2) pick one.

Posting links to those boards is in part a demonstration that such boards exist.

I believe so. There are premade splitter cables that separate pins 2 and 3 from a DB9 into two more DB9's, or such a thing can be made, or (preferable) one can use a CPU with two serial ports (or USB split into two ports). The splitter cable can be inside the box since IIRC you don't want it flopping around on the outside. Then the two DB9's would be on the rear panel.

Reply to
Paul Rubin

Excellent Don. Now, please tell me which unit is the DCE and which is the DTE? Or better yet, just answer the question asked, on this device, which pin on the DB9 connector is the data output and which is the data input?

Reply to
Rick C

Sorry I meant DTE, not DTR. DTR is one of the signal pins. I believe I got the assignments right for DCE but maybe not. Anyway there are only two possibilities, and it's very easy to get stuff switched around someplace, so one always has to check.

Reply to
Paul Rubin

You are providing links to hardware. I'm asking you which pin is data out and which pin is data in? This is a very simple question, no?

Do you know if that splitter will work for this application? I don't see the link. How many messages back, or how many days/weeks ago was that? You posted a lot of links in the message I replied to.

Can't use a USB dongle if there's no USB software.

Having a UART is not sufficient. The interface needs to be a DB9 male, RS-232 voltage levels. One connector for the input data, and one connector for the output data.

That is far outside your concern.

Have you picked one yet?

I've never needed convincing that these boards exist.

Does the splitter cable run a signal to pins 2 and 3 on both cables? I've yet to find one that connects to pin 2 on one connector and pin 3 on the other connector, leaving the other pins 2 and 3 unconnected.

I think you will find the splitter cable will need to be a custom design. It's probably easier to just use a CPU without a DB9 and build a cable to run from the header to the two DB9s on the box. But then you will need a CPU card with RS232 level shifters.

This is why I don't want to do the design. It's messy and far too much work for something so simple.

Reply to
Rick C

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.