HMI panel without PLC


Thread Starter

Levent Komurcu


I'm designing a telemetry system for our solar car. We are using Moxa UC7420 embedded computer which has 8 RS232-485 ports also using WinCE as OS. There is no problem with that. But we want a display, preferably tp170, to show some info about the vehicle and what he/she needs to do.

As there isn't any PLC around there, how could we send information to the HMI? I think that is possible with RS485 but I need some starting point.

Thanks in advance.

Daniel Chartier

Hello Levent;

One suggestion would be an OPC connection between Excel CE and the operator panel. The TP170 (A or B) supports one OPC DA server connection over TCP/IP; you can buy an add-on OPC client for Excel CE from Matrikon or EasyOPC, for example.

For more details, you should look at the WinCC Flexible 2005 Kommunications, T1 manual; the TP170 Operating Instructions; and Google for Excel CE OPC. Then write whatever data you want transfered to the operator panel to specific cells in an active Excel CE sheet (through whatever software you are using for your controls) so it is read/written to the panel.

Hope this helps.
Daniel Chartier

marc sinclair


Do you mean the TP170 Micro? If so, this has been superseded by the TP177 Micro. It was designed to work with a PLC so other uses could be a bit tricky. The TP177 Micro runs Linux, and source code is supplied so it's possible, I suppose, (I've never done it) to reflash the unit with your own code, but it may be as easy to build your own.

Marc Sinclair
You may use Modbus Master on the embedded computer and then set tp170 to communicate over Modbus to computer.

Curt Wuollet

Why not simply use a terminal or PC configured as a terminal rather than get into decoding some proprietary garbage. If you need graphics you could use Glade or another free GUI builder and keep things as simple as possible. Just decide on a packet of the things you want to display and write a small C routine to receive the packet and write the contents into the appropriate places. That would likely be easier than faking enough of someone else's general protocol to get the job done. With Glade or TCL, you could have something that looks impressive in a day or two. That's what prototyping languages and GUI builders are for. And they are free. Or if what you need is small and functional there are lots of vendors for RS232 displays of the type modders install in their PCs to display their attempts at processor cooking. Starting with what you need or with a published, encouraging protocol will make things much easier. I've done this sort of thing to add a display to an otherwise headless PC control project or for a simple user interface with a few buttons. Commercial HMIs tend to be simple only when used with the gear they are normally sold with. And very spendy.

One way would be to study a common and widely supported industrial protocol (for instance, Modbus RTU for serial or Modbus TCP/IP for Ethernet), and communicate your data in that format to the HMI. A benefit from this approach would be flexibility - you aren't wedded to a particular HMI, and can fairly easily re-develop the screen configurations for other brands and models with (ideally) no changes in the embedded code.

Did a Google search on the string, "modbus sample programming code", and one of the returns on page one was from Moxa's site offering free source code downloads for Modbus serial & TCP/IP conversion.

I haven't worked with Siemens much, and never with their HMI products, but that TP170 part number puts me in mind of them, and don't know what protocol drivers are supported (almost certainly Profibus, though, since Siemens was a major factor in its development).

Also looked up the UC7420 specs, and saw, at least in the PDF I downloaded, it is usually configured with Linux, and has a spate of useful googaws like a FTP server, Apache web server, etc. Was wondering - if all you want to do is display information, and don't need any major user interaction would it be possible for you to create several HTML pages instead? No, I suppose not ... looked further, and it seems to have internal driver support for it's own LCM in 16 col x 8 row text mode only, so you'd need another computer just to run the browser.

Nope, I'd see how much work was involved doing it using Modbus, and, if not too onerous, jump to it.

Michael Griffin

I think you actually want to use an operator terminal which has an open protocol, not try to reverse engineer a proprietary one. Search on Google for "oem operator terminal", and you will find lots of hits.

I had a look at the specs for the Moxa UC7420. It already has an LCD panel interface. You can buy compatible panels (128 x 64 pixels) from a number of sources. You would have to do more work mounting the device, and you might have to get out your soldering iron, but it would be much cheaper than a serial terminal.

Mr. Wuollet had a suggestion of using a PC as a terminal. You could take that further and get rid of the Moxa computer and do the control on the PC. Have a look at the discussions we had about Mini-ITX computers and booting from flash under "APPS: Cheap DAQ cards?" for more information.

Levent Komurcu

Thanks for all the replies. Building my panel looks much easier than getting into complicated HMI protocols. Also, as you said, there is no need for complicated user interactions. For this reason 5-6 buttons will do the job. For all of those reasons that you have been supressed I have decided to use a 128*240 LCD and PIC micros over RS485 protocol.

Thanks again.