I hope I'm not OT here. If I am, please let me know.
I want to design the following: I've written a special software to control a lot of measured data. If the measured data drops down and falls below a selected level a warning must come up. I do so within the software. But in addition there must be an LED panel which shows the alarm status via a (blinking) red LED. The panel is far away from my computer. So I had the idea to address it via the local network.
My question is: Does anybody have an idea to address about 250 LED warning lights via ethernet (TCP/IP socket) not using a PLC? Maybe a little electronic circuit with a TCP/IP controller chip (which receives a command that sets a specific 8-bit pattern) and a chip that interprets the incoming bit pattern and sets 256 digital outputs. This circuit must be cheap and should be set up by a non-electrician-engineer ;-)
If you want to do just one a PLC may be cheapest. Alternately, a PC-104 stack with a processor, digital I/O board, and a bunch of software would work. The nice thing about the PC-104 solution is that you already know your way around a PC.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Yet another idea would be to use an old laptop at the remote location. If this is a one-up project in a company you are probably retiring many laptops per year, most of which will have a built-in network card. That way your technicians don't have to mess with the LAN setup, especially if you are using DHCP already.
Since older PCs still have a parallel port the addressing of the LEDs should become pretty trivial.
1) You need a small (cheap?) processor board with Ethernet.
2) You need to light up 250 LEDs.
For 1), the Rabbit modules from
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have already been mentioned. All you probably need is a "RabbitCore" module - this has the processor, Ethernet connector, and digital I/O ports. The modules are programmed in a language that is almost C and not too hard to learn. The compiler comes with lots of example applications, including ones that use the network. This will probably cost you US$200 or so.
Another option is the Ethernut,
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. This is a small processor board with Ethernet. You can get a C compiler for it, and both the hardware and software are open source. The German distributor sells the Ethernut 1.3 board for about EUR140.
Finally, using an old laptop has been suggested and might be the cheapest option if you have an old laptop. If the indicators don't have to be LEDs, you could even display them on the laptop screen. You probably don't even need a hard drive... Put DOS (or FreeDOS) on a floppy, include a driver for your network card, and run a terminal program like IVT
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. In your software, write a routine that displays the desired output, using vt220 tags (these include blinking characters). Use IVT to Telnet in to your host program and display the output.
For 2), you are on the right track, but you really only need 32 digital outputs. You can connect the LEDs in a matrix and and scan the rows and columns to light them up. If you scan fast enough, the LEDs will look like they are always on. Here is an example using 16 LEDs and 8 outputs:
(view in a fixed width font)
W -+----+----+----+ | | | | | V 1 V 2 V 3 V 4 V = LED --+-- = connection - - - - - | | | | | | +--+ +--+ +--+ +--+ | | | | X -+----+----+----+ | | | | | | | | | | | V 5| V 6| V 7| V 8| --- = no connection - | - | - | - | | | | | | | | | | | +--+ +--+ +--+ +--+ | | | | Y -+----+----+----+ | | | | | | | | | V 9| V A| V B| V C| - | - | - | - | | | | | | | | | +--+ +--+ +--+ +--+ | | | | Z -+----+----+----+ | | | | | | | | | V D| V E| V F| V G| - | - | - | - | | | | | | | | | +--+ +--+ +--+ +--+ | | | | 1 2 3 4
If you connect W to +V and 1 to ground, LED 1 comes on. If you connect Y to +V and 3 to ground, LED B comes on. And so on.
thanks a lot. This was a great proposal. Looking at your LED matrix there is one point I don't understand. Considering the following example: You want to light the LEDs V1, V6, VB and VG. It is the diagonal from the top left to the bottom right. In this case you'd have to connect the contacts W, X, Y and Z to +V and the contacts 1, 2, 3 and 4 to ground at the same time. But if you do so, all LED will flash. The problem is, you cannot control a set of LEDs (a special pattern) in a unique way.
Do you have any idea how to cope with that?
Please note: the LEDs should signalize some status and they must be controlled independent. A single LED must be switched on and a set of LEDs must be switched on independently.
You only think that a set of LEDs must be switched on independently. Think about the monitor you are reasding this on. (If you have an LCD monitor, go out and buy a CRT before reading further...) It sure does look like the entire screen is turned on with no limitations on the pattern, doesn't it? In reality only one tiny spot is on at any given time. LED matrixes are the same way; in general a display with 50 LEDs on and 50 LEDs off never has all 50 on at once. It eaither lights one row at a time, one column at a time or one LED at a time. You eye integrates the rapidly flashing lights into what appears to be a steady glow.
What you do is to only connect one of the W, X, Y, Z lines to +V at once, and only one of the 1, 2, 3, 4 lines to ground at once. The LEDs that are lit are not on for 100% of the time. If you do this fast enough, your eye perceives an LED that is lit all of the time.
The lights in your house work this way. They are actually flashing off and on 100 times a second, but this is so fast that you see a steady light. Most LED clocks have this kind of display; try eating some crunchy food while looking at an LED clock and you will see the digits shimmer and move around, because your eye is in a different position each time the LED is lit for a fraction of a second.
To display the LEDs 1, 6, B, and G with the matrix I used, the logic might go like this:
Connect W to +V. 2. Do I want to turn on 1? Yes! Connect 1 to ground. LED 1 turns on. 3. Disconnect 1 from ground. LED 1 turns off. 4. Do I want to turn on 2? No. Continue. 5. Do I want to turn on 3? No. Continue. 6. Do I want to turn on 4? No. Continue. 7. Disconnect W from +V.
Connect X to +V. 9. Do I want to turn on 5? No. Continue.
Do I want to turn on 6? Yes! Connect 2 to ground. LED 6 turns on.
Disconnect 2 from ground. LED 6 turns off.
Do I want to turn on 7? No. Continue.
Do I want to turn on 8? No. Continue.
Disconnect X from +V.
Connect Y to +V.
Do I want to turn on 9? No. Continue.
Do I want to turn on A? No. Continue.
Do I want to turn on B? Yes! Connect 3 to ground. LED B turns on.
Disconnect 3 from ground. LED B turns off.
Do I want to turn on D? No. Continue.
Disconnect Y from +V.
Connect Z to +V.
Do I want to turn on C? No. Continue.
Do I want to turn on D? No. Continue.
Do I want to turn on E? No. Continue.
Do I want to turn on F? Yes! Connect 4 to ground. LED F turns on.
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