RS232 Multiplexer...HELP required please.

[Wilksey]

I have a simple (heh yeah right!) idea for a time saving device, but need some help implementing it.

I need to switch 4 to 8 RS232 devices to one.

What I am after is a simple way to switch one device (PC) to multiple end points (GSM modems, linux console, voice modems etc) without having to keep unplugging cables.

Various things have been suggested, such as USB to RS232 adapters and Ethernet, and PIC's.

USB to RS232 adapters are messy and they dont always keep the same port number, particularly on the cheaper ones, so I dont want to use these. Messy with cabling everywhere for 8 ports at least.

Ethernet isn't available on the devices.

PIC's, whilst a good idea, isn't format independant, I would have to bit bang 8 software ports at 7E2.

I have some 74HC154 chips and thought paired with some MAX232's for level shifting would do the trick, I have been told that this wouldn't.

I have seen this:
Homebrew Designs - Serial Port Multiplexer

But the 150 isn't readily available, so I was hoping to swap it out for another 154.

Any help / assistance appreciated!

Regards

Wilksey

 

[blueroomelectronics]

Are you hoping to make this a commercial product? Sounds like more trouble than it's worth.

 

[Wilksey]

Nope, just to make things simpler for myself.

If I could get logic switching it would be very simple, if I had to use a PIC then, yes, it would be more trouble than it's worth.

Didn't think it would be that hard to be honest.

Figured an old school electronic tech could help with a simple answer.

 

[BrownOut]

I can't make heads of tails of the schematic. And I don't think it's what they built.

 

[Wilksey]

I understand the schematic, just dont understand if I can replace the 150 with another more readily available logic chip.

 

[BrownOut]

The 74HC151 is an 8:1 multiplxer, and is available from many suppliers. NXP|74HC151N|IC, 74HC CMOS, 74HC151, DIP16 | Newark.com

Not pin compatable, but will work.

 

[Wilksey]

Aha,

Actually, I would suspect that the 8:1 would be more suitable for my application as I only need 8 outputs max.

I'll have a look closer at the chip.

Thanks

Wilksey

 

[KeepItSimpleStupid]

Just put the stuff on the network with a few serial to USB converters, a USB hub and a Silex Technology SX-3000GB. Eventually, I plan on putting a Skype gateway and a modem to the network.

I think there are products that can do exactly what you want. They operate with a virtual serial port driver. Lantronix, Moxa and Sewell techology are possible starts.

 

[blueroomelectronics]

RS232 voltage levels can be as high as +15 to -15V
TTL ICs won't work at those levels, some CMOS might. Of course a quality USB to RS232 multiport adapter like Digi's would work fine. Also most old RS232 devices now exist as USB devices. Modern laptops don't have RS232 ports and stationary PCs rarely need GPS.

Ahh, missed the MAX232 part.

 

[BrownOut]

UART's and other suppporting functions work at logic levels. The +/-15V is only for the physical medium. Any other functions, like multiplexing, will be perfomed by logic.

 

[KeepItSimpleStupid]

Example product: Moxa Device Servers NPort

 

[OlPhart]

make it easier...

Do the level shifting then use analog muxes; digital is crisper but direction requires design. Don't bypass level shifting & try to go direct through the muxes, ANY surge will destroy them. A 4051 will do well. Good Hunting <<<)))

 

[Mr RB]

You can buy rotary switch multi-port selectors!

I have a quad parallel port one here and I'm sure you can get quad serial port ones too. They used to be common in offices some years back but a google search should still find some in stock somewhere.

 

[ADWSystems]

If there aren't chips available to multiplex +/-15 RS232 signals then you'll need to go with what you've got. Install an array of MAX232 chips to convert to 5V logic then multiplex the 5V signals and convert back to RS232 into the PC.

 

[4pyros]

What I am after is a simple way to switch one device (PC) to multiple end points (GSM modems, linux console, voice modems etc) without having to keep unplugging cables.

What operating system is on the PC?

Various things have been suggested, such as USB to RS232 adapters and Ethernet, and PIC's.

You need an old school Rocketport cheak E-Bay or
https://www.amazon.com/Rocketport-Infinity-express-8PORT-Interface/dp/accessories/B000WU2FO2

But the 150 isn't readily available,

Why not? Digi-Key has them # SN74150

 

[Diver300]

I would buy a couple of these:-

**broken link removed**

If you connect the computer to both of the switches, you can select between 8 serial devices. On the switch that is not in use, you will probably just have to press one of the buttons a bit, so that all four buttons are out. That will make the switch disconnect all four ports, so the other switch can connect one of the other four serial devices.

 

[Wilksey]

Hi Guys,

Thanks for all the answers, i think i'll try the TTL switching, as I have MAX chips around I can use anyway.

I know some CMOS can switch RS232 levels, but I think it is safer anyway to use MAX232's.

Cheers

Wilksey

 

[Magdaw]

Hello. If you want to do what I needed to do - capture multiple streams simultaneously and weave them into output to one RS232 port on the PC - then a PIC may be a good way to go.
The PICs can run at respectable speeds 20MHz for example (5MIPS) which is plenty to read the input streams and weave them together into a simple packet-based output stream. (Also need to do this the other way of course if you need full duplex, but the same PIC could manage it.)
The other thing you would also need is a demultiplexer program to run on the PC to de-tangle the streams and feed them to their respective consumers. If each stream uses, say DC1 (ascii) and follows it with a channel number and a packet length then payload it's quite simple to do. Fun little project anyway.

 

[granddad]

I would use a cmos 4067 analogue multiplexer 1 to 16... or.... 16 to 1 !

 

[JimB]

WARNING!

Four year old thread alert.

JimB