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USB or Ethernet to replace RS232?

M0DCD

I have had a discussion about this in email, on the subject of replacing RS232 interfaces with either of these two options.

 

My points are that if the item only needs local connectivity (ie download data, setup machine etc) then a generic USB solution such as provided by the FTDI modules is adequate, rather than have to go through having to redesign an existing product. Field service seems to be one application where the technology has run forward (you try and find a laptop with RS232 on it these days). Yes you could use a dingle, but then doesn't Windows keep changing the port number for you?

 

TCP/IP is nice, but if you don't need the machine permanently connected to a network or just have a basic interface, it may be too good a solution. Yes, you can add extra features and a web interface, but would a water level monitor (for instance) that only communicates twice a year need this?

  • I think the correct answer is both, or both and others. RS232 used to be almost the only commonly used port on a PC, so naturally all serial peripherals were based on it. Now we have many types of ports and applications use the standards that suit them best. USB and all its iterations including the new wireless standard look good for short range applications especially. Ethernet can carry more data over longer distances, so it is used for the applications that require these specifications.

     

    We also have to consider wireless protocols like Bluetooth, Zigbee, WiFi, WiMAX and others, which have found their own specific niches. In my opinion we will never see another unified standard like RS232.

     

    If the FTDI modules and chips can let you retrofit and get the features you require, than it is a good idea to use them. For your water level sensor example, Zigbee would be a decent shout, or Bluetooth if it requires laptop connectivity, but these would require a redesign. I can see these type of applications using energy harvesting modules, ultra-low-power MCUs and Zigbee connectivity in the near future which should provide up to ten years self power

  • in reply to awinning

    RS232 has been round for a very long time in engineering terms, and for short distance links it has worked well, remembering back to the 1970's when a 9600 baud rate was fairly exotic. Most of the applications I have seen industrially has been to set or read parameters in equipment or diagnostics where this low data rate isn't an issue. Limiting physical access to the port is a very good solution in such as vending machines, if it's using wireless technology it could leave potential "back doors" open.

     

    Where they are possibly only a few hundred units in service, the amount of work to develop a Zigbee solution becomes a big part of the project cost, and there are a lot of these small projects out in the wilds. My opinion is that Zigbee hasn't settled down as yet, there are still issues between the technology providers where the extensions don't cross over suppliers.

     

    It's not a case of retrofitting designs, if it's changed to TCP/IP or Zigbee it's a fairly large redesign job, whereas adding modules to an existing PCB whose design may go back years is much easier. In the present climate this is a reasonable solution, especially as some industries don't seem to ever be too keen on adopting new technology (utilities, railways etc).

  • We do a fair bit of RS232 because its easy to use and has been around since the electron was discovered imageand we use the FTDI modules. Out in the field we use a Netbook running Linux rather than windows with VMware Worstation (on a laptop running Linux) to run any legacy windows apps. Frankly adding a USB dongle is the best option and if it gets zapped by some surge or other you replace the dongle not the whole shebang. Netbooks running Linux are terrific for field engineering, light small long battery life and don't cost an arm and a leg to replace if they get thumped. A bit off topic I know but RS232 has shifted out of the mainstream so I would suggest dongles and commodity hardware is the way to go.

  • in reply to M0DCD

    Ironically, I did mention using the dreaded SCC devices in Field Service, but someone said they hadn't a clue what they were. I'm not sure if they give you Hyperterminal in Vista, but for those in Linux will probably find communicating with KTerm (or similar) does exactly the same. Not that you'll ever configure the port to anything other than 9600,N,1 anyway.

     

    Fine about the dongles, yes they are cheap enough to replace on a regular basis, they aren't designed to be rattled round in the bottom of a toolbag, but as it's been a long time since laptops has RS232 and netbooks never even considered them. I have an EeePC701 myself as well as a full sized laptop and not a copy of Vista in sight.