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Basic Electronics » LED Sign Help - How to control words

April 25, 2011
by petek157
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First off I appreciate the business model of sell to educate. Rather then sell and forget about it. I am excited to work on my first project with the NerdKit.

Topic at hand. I bouoght a LED sign from a government auction not really even expecting it to work (for the price I paid). It worked perfectly. The problem is that it didnt come with anyway to change the message that it displays. I am hoping that someone might be able to guide me to being able to control this sign. Here are a couple pictures and a video to aid everyone to possibly helping me get this thing up and running.

board1 board2 board3 modem

Sign Video

Any help on this project would be greatly appreciated. If you need anymore information please let me know.

Thanks,

April 25, 2011
by bretm
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The pictures are too small to see the detail on the chips, but that looks like a Zilog Z80 CPU. I can't watch the video from here, and from the pictures I can't even tell where the LEDs are situated or how they're controlled.

But that big old 56kbps modem suggests that they programmed the message by phone line, from a central office, and the sign stored the new message in some kind of non-volatile storage. I'd guess you'd need to figure out the protocol they used to send a new message to the sign.

April 25, 2011
by hevans
(NerdKits Staff)

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Hi petek157,

Sounds very interesting. There are two directions you could try taking this, the first is to try to figure out how these things are supposed to take a new program, the second is to try to highjack the array at some point and just force it to display what you want. I very much suggest you try the first approach. The first thing I would do is google every brand name, product number or serial number you can find on the thing, it will probably give you some clue. Are there any clues you can see on the device? Any connectors that look like they might connect to a computer, or keyboards?

Humberto

April 25, 2011
by bretm
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These guys make LED signs containing US Robotics 56k modems. Maybe related?

April 25, 2011
by bretm
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Look at this PDF for government bureaucracy at its finest. Section 6 of the doc describes a DOT standard for communicating with Variable Message Signs. You might be up against something like that.

April 25, 2011
by bretm
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DTSC2D might be a Daktronics Sign Controller.

June 03, 2011
by petek157
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OK I have finally found a bit of time to start monkeying with this sign. I figured that I would try the obvious first and just hook into it..... Well right off the bat Im not sure where to start. it has an 56k external modem built into it. So I figured just plug the computer into it..Well thinking about it I dont know if you can plug directly into a modem from a computer with a modem. Dont you have to "dial" in. and if so, I only have one phone line here at my store. It looks to me that they just had the sign plugged into a phone line and dialed into it from another location to program it.

So I guess the question for the time being is can I "call" directly into the sign modem from my computer with a modem with out plugging into the phone line? If so how? If not any other suggestions on "dialing" into the sign modem with only on phone line on site?

Thanks in advance. Peter

June 03, 2011
by 6ofhalfdozen
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Heya Peter,

I was just looking at those photos and video again. I saw a few things I missed on the first few looks, and hopefully they are things that will help you figure that board out.

First off, it looks like they have hacked up the cable coming out of the modem. Can you tell if that is 25pin serial, parallel, or centrix?? Can you tell where those wires go from the back of the modem to?? Is is possible they are pulling +12v power for the board from the modem via a pin on the connector as well as data timing and communication? If you can figure out what they were doing with the pins coming out of the modem, you should hopefully have a better handle on what is going on along the big board. Hopefully.

On the big side of the board, in the video there are three wires (red, green, ?white?) the go into the board from a big wire. Just below that is a silkscreen indicating COMPORT. Is this where three of the wires from the modem end up? If so, this might be your RX, TX, and Grnd.

There is a silkscreen for a long bar of pins/holes earlier in the video that looks like it says power below it. There are two wires that come into this. Again, is this two wires from the back of the modem??

I agree with Bret, that definately looks like a Zilog Z80 cpu. dunno what all that means for controlling the board, but should be able to find a datasheet. And a datasheet for a semi-known chip is way better than no datasheet for an unknown chip.

If you do need to "dial in" to the modem to communicate with the led board, there used to be a cable for it. I can't remember if it is a true null modem cable or a patch/cross-over, but there did exisit a cable for letting a modem talk to a modem via direct wire and no phone system. I got rid of most of my modem stuff a few years back, but I had a couple. I want to say I used Comit or hyperterminal to communicate, but it was never exactly easy. if you can sort out what the board wants, you might be able to program your Nk to talk and command the board.

anyhow, hopefully there was a little usefull insite there for you.

June 03, 2011
by Rick_S
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You could most likely eliminate the modem altogether and just tie the RX/TX/GND to a serial port on your computer. Now the controller computer in the sign may expect AT commands to answer... for instance if a modem is dialed into through a phone line it will send RING to the computer. So you may find if you type RING from your pc that the board will respond with something.

I noticed there is a keyboard header, a battery backup (yellow cell) probably to preserve the stored message through power down, a real time clock (that big Dallas semiconductor part), a RS-232 communications section etc...

Zilog Z80 cpu's are probably one of the most widely used cpu's in history. They have been in use since at least the early 80's and actually were the main CPU in early computers (PRE-IBM PC). They have been shrunk down and can often be found in modern electronics where a simple cpu is needed. Micro-controllers will most likely be their death because they pack a lot more power.

My guess -- and this is just a guess -- is that that controller is in fact a low level computer that controls the signs operations. The display itself most likely has other circuitry such as shift registers etc... to interface to the display computer. I noticed there is an EPROM on board next to the CPU. Does the white label on it say anything of interest?

Rick

June 03, 2011
by petek157
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To - 6ofhalfdozen

"Can you tell if that is 25pin serial, parallel, or centrix?? Can you tell where those wires go from the back of the modem to??"

Dont know how to tell the difference

"Is is possible they are pulling +12v power for the board from the modem via a pin on the connector as well as data timing and communication? If you can figure out what they were doing with the pins coming out of the modem, you should hopefully have a better handle on what is going on along the big board. Hopefully."

I dont have enough expierence (yet) to tell what the wires are doing. I can tell you that (Pic included) the Blue wire is jumped from pin4 to 20 on the modem cable, Red is Pin 2 to comport, Green is Pin 3 to comport, and White is pin 7 to comport.

"On the big side of the board, in the video there are three wires (red, green, ?white?) the go into the board from a big wire. Just below that is a silkscreen indicating COMPORT. Is this where three of the wires from the modem end up? If so, this might be your RX, TX, and Grnd."

Yes these are the wires coming from the modem.

"There is a silkscreen for a long bar of pins/holes earlier in the video that looks like it says power below it. There are two wires that come into this. Again, is this two wires from the back of the modem??"

No these wires go to what looks the backup as Rick called it (Pic included)

Rick I will post answers to your question tomorrow. I have to run.

Thanks guys hopefully with the forums help I can get this darn thing working.

June 03, 2011
by petek157
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Shoot - I will post the pics tomorrow too. - Sorry

June 03, 2011
by Rick_S
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6ofhalfdozen, I'm sure the port on the back of the modem is a standard DB25 serial connector and most definately NOT a parallel interface. (BTW, the parallel interface I think you were trying to refer to is centronics not centrix and is a larger 36 pin connector found on old printers) An old style parallel printer cable would have a DB25 on one end and a Centronics on the other. Telephone modems of the type in this display by US-Robotics to my knowledge were all serial... I probably still have one lying around somewhere :).

As for the wires on the modem, it looks like they just soldered wires to a plug and plugged into the back of the modem. The three wires then go from the modem to the communications port on the signs computer. Chances are the chips on either side of those three wires are something like a MC1488/MC1489 transmit recieve pair. The big square chip next to it is probably a UART maybe a 16550 or similar.

Rick

June 04, 2011
by petek157
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Sorry for the delay in getting the pictures posted.

Picture of serial connection. Serial Connection

Wires going to the COMPORT COMPORT Wires

Where the wires from/to the power section of the board goes. From/to Power

As for the white label it is pretty hard to read. Best I can make out (pic below) is; SGN128mZ - SG8SCAN - 11/23/98 RDB

White Label

Rick - Your possiblity sounds logical. Again I have very limited experience in this stuff right now so if that seems like my only option at this point I may need to ask for your expertise in doing so. After doing some research it sounds like programming over is pretty much my only option outside of finding someone that had this companies (now closed) software.

SO.... That being said, anyone up for the challenge?? If anyone has more questions please ask.

June 04, 2011
by Rick_S
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Well the square chip was as I guessed only an older version. It's an 8250 UART. The chip above the modem wires is the equivalent of a MAX232 and it's how the uart talks to the outside world... (It's a part worth your parts box if you can remove it without destroying it).

You are probably correct in that you will have to develop a new driver board for this. That would mean removing the board with the z80 and the modem. Probably leave the power supply. My guess is that there are a lot more components in that display. If you remove the LED panel there are probably a bunch of shift registers of some type there that you will have to figure out how they are used to develop a driver circuit for them.

Rick

June 04, 2011
by Rick_S
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After looking again, the DS14C232C is socketed --- definately a parts box keeper.

June 04, 2011
by Rick_S
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I was wrong about the dallas block though, that is the ram for the computer-- it's 256k non-volotile SRAM. The memory for the z80.

The part with the sticker is probably the boot rom (EPROM).

Rick

August 24, 2012
by petek157
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WOW, I have to apploigize to all of you that were helping me....OVER A YEAR AGO! Time flies. I got busy with work so as you can tell this project got put on the back burner.

That being said....IM BACK!

My thoughts on this project are along the lines as they were before. But I think working backwards as was somewhat suggested above is they way to go starting at the LED boards (which I have removed).

Board Connection

IC Chip

Array

So....

Any advice would be helpful on what would be my next step. I mentioned above that I am by no means educated in EE or programming. So dumbing it down for me till I start picking it up would be greatly appreciated. I see that the pics above have been removed Im sure because its been so long. Seen as it sounds like starting at the lights and working backwards is the plan I dont know if we need them. BUT if you would like them in order to weigh in just say so and I will get them up.

Ask me anything, make suggestion etc. I appreciate any help I can get.

Ultimate end game would be being able to control this guy using DMX so I can use some Christmas light animation software (Light O Rama) that I already have. But I will settle for getting to work anyway possible.

Thanks Pete

August 24, 2012
by dan_engbers
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Can't see the original pics with the serial port, but did you try connecting the serial directly to your PC and opening something like PUTTY? Just choose serial, enter the correct com port (you might have to mess with port speeds unless the 56K modem is set with the dip switches) and hit ENTER. Or turn the sign on and see if throws some feedback into the Putty session.

The modem itself handles everything up to the communication directly with the unit so you don't need to know the modem mumbo jumbo. The issues is what the sign gives you once you are connected.

If the modem isn't using 9 pin parallel, look into an adapter to take it from whatever the modem is, to a 9 pin. You should be able to get one for a couple bucks.

August 25, 2012
by Ralphxyz
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Chances are the modem was just for communications to change the display not to actually display anything.

If you power it up is anything currently programmed?

Ralph

August 25, 2012
by Rick_S
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Like I said in an earlier post, chance are the onboard computer of this display could communicate with a micro via rs232 but you would have to pretend the micro is a modem because the computer is expecting a modem. So if you monitor modems, when the phone rings the modem responds "RING" the computer would then respond with an "ATA" To answer. Once connected, the modem would respond with "CONNECT". At this point communications would proceed.

August 25, 2012
by dan_engbers
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Ralph, I will still attempt a connection to see if a small UI were programmed with the unit. It would take very little time to test that out.

Rick, no modem = straight serial. No need for AT commands with the modem gone. The modem commands are used to interface with the modem itself, not with the bits behind the modem.

We use modems all the time to connect to serial ports remotely for routers and network appliances. Without the modem all it takes is a serial connection.

August 26, 2012
by Rick_S
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The difference between this and your comuputers is you have the ability to control both ends of the conversation. Thus if you pull the modem, you can communicate directly w/o commands because the software that was issueing the commands to the modem is no longer being used or not being used in the way it was.

In the case of the display, you cannot control what is being transmitted at the display end. Its onboard computer (the Z80 board) has hard coded software that is expecting a modem at the other end of it's rs232 port. The sign may even issue AT commands on powerup to ensure the connected modem is configured in a certain state waiting for a call. It will most likely be in a mode expecting to see "RING" come in on its receive line indicating an incoming call. This is how many of these message boards over the highways work. They are simply controlled remotely by a phone call to a modem. Once the modem negotiates a connection with the sign (The part you would have to mimic), a login screen of some sort (Text based I'm sure) would probably appear. If not, the software at the sending side would just issue either commands or the message itself.

August 26, 2012
by dan_engbers
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gotcha.

August 27, 2012
by petek157
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I am working on either making a converter cable or finding a computer with a serial connection. Neither of mine have serial ports. In the mean time I found this on a LED light store that I watch for christmas lights. Is it possible that I can make this work until I can make something that would allow me to have total control of my array.

http://www.aliexpress.com/product-gs/492773412-LED-Remote-Controller-card-max-16-256-or-32-256pixels-MOQ-1set-wholesalers.html?url_type=wto_clc_pic&productId=492773412&biz_type=sitePromo_wto_buyer360_clc&crm_mtn_tracelog_plan_id=764310354&crm_mtn_tracelog_task_id=13743579&crm_mtn_tracelog_log_id=1990817133

Let me know what you think.

Thanks again, Pete

August 27, 2012
by Ralphxyz
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There are USB to serial converters without a $30.00 shipping fee.

Ralph

August 27, 2012
by Rick_S
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That looks like a neat gadget for controlling an LED Array. I don't know if it'd work on your array as drop in replacement for the built in controller though...

Rick

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