How to use a scrolling display board



  • So I had this old commercial scrolling display that was not working It has 16 - 7 Row 5 Column LED matrix displays on boards of 2 each. These are mounted on a long board with TC4094BP 8-Stage Shift-and-Store Bus-Register chips and DS2003 High Current/Voltage Darlington Drivers. I am trying to figure out if there is a way I can make use of this as a MySensors display similar to the scrolling text sensor node created by @AWI. I desoldered 3 of the display boards to find out what chips it was using and to get a better idea on how to connect things. I have mapped out the connections for strobe, data and clock that are connected to the shift register chips. I have also found the row control line connections, but I am trying to figure out how I can make it all work. I think it may have been a dual color display, but I am not sure. Having a hard time finding information on it.

    Here are a couple pics:
    top view
    chip view

    Does anyone know of any schematics and/or libraries that may help me control this? I can take more pics if anyone thinks they want to see things further, possibly the solder side of the board, or pics of one of the matrix modules.

    Thanks for checking this out.


  • Hero Member

    Looks like a betabrite sign. I use some with HomeSeer to display weather info, sports scores, etc.



  • I believe it was a betabrite sign. It was dead though which is why I salvaged the display. If I can just figure out how to multiplex the matrix I think I might be able to do something with it. I may have to take one nano just to multiplex and another to do the MySensors stuff. It is just taking some time to figure out and understand how to do the multiplexing with the shift registers. If anyone has any good resources on this I am all ears.


  • Hero Member

    I've never been able to find any schematics for them. I have one that doesn't work as well, but have not taken it apart yet.



  • @Sparkman,
    I have had this one for a number of years. Tried to see if I could fix it a while back, but had no luck. The biggest thing as you mentioned was that I couldn't find any schematics. So recently I just decided, to hell with it, I am going to salvage the display. the long PCB that the displays are mounted to is a single sided PCB, so once I desoldered the 3 display boards from that and saw the basic layout of the chips and what not, it was pretty easy to map most of it out. I may try to create my own schematic as I map it out to better help me design the arduino circuit. I don't see any decent markings on the LED matrix boards to find a pinout for those, but I don't think those are going to be that hard to map. I just need to create an LED circuit with a battery/power supply and a resistor to see if I can map the rows and columns. If you look at the pic I posted of the top side of the display board with the chips, you see the top connections are PC1, PC2, PC3, etc... and the bottom side is PR1, PR2, PR3, etc... I can only assume that the PR is the rows and PC is the columns of the matrix. I'll use that info as I test. Mapping the strobe, data, clock lines, etc... was pretty easy. I just have to figure out how the shift registers are cascaded.

    The main control board had a bunch of transistors that I would assume were to drive the current needed to run that many LEDs, so I may try to salvage those too to use in my circuit. I never had the original power supply, but I am guessing that it had to be in the range of 3 to 4 amps to drive all of that, so I'll have to find me a switching supply that can source that much. Do you by chance have the original power supply for yours? If so, was it an AC or DC supply? I am wondering if mine was an AC supply because the main board had a full wave rectifier on it.

    I'll let you know if I figure out any more.



  • OK, so I mapped one of the LED matrix boards. I found that it is a dual color display with red and green. Here is how the mapping goes:
    mapped LED matrix


  • Hero Member

    @dbemowsk Yes, I do have the power supplies. They are 7V AC rated for 5A:

    0_1480215890722_temp.jpg

    I've never seen 7V power supplies before, so probably not easy to find. Is there a 5V regulator on the board?

    Cheers
    Al



  • LM2940CT low dropout regulator. I am guessing it was used for 5 volt regulation with an input voltage of 7 volts. It has 4 - 4700 uf electrolytic caps too on the power side.



  • Here is another update on my progress. I have mapped out the display board connections that went to the main control board. I did have a minor problem when dismantling it. I lost the solder pad for the VDD connection, but I should be able to repair that with some copper tape. I think with this information I should be able to make this work.
    Display board connection map

    The transistors on the control board that I am assuming controlled the rows are Motorola JE210 PNP transistors. They appeared to be driven by more shift registers. These were slightly different from the ones on the display board. These are TC4015BP shift registers, whereas the ones on the display board were TC4094BP shift and store registers. Those also drive ULN2003A High-Voltage, High-Current Darlington Transistor Arrays which are similar in function to the DS2003CN arrays found on the display board. It looks like those are what drive the JE210 transistors.

    I did some searches on the net to find info on controlling a similar display with an arduino and I found this. According to that link they are using 74HC595 shift registers to drive the rows (and columns) of their display. They are using a single color display, but I should be able to adapt this with 2 shift registers to get the 2 different colors to display. They also have some arduino code to test it out with. This should give me a basic start.

    @Sparkman, this is probably very similar if not the same as the display that you have. This should be enough information for you to make use of it.


  • Hero Member

    @dbemowsk Thanks for posting. Mine are the 8 color variety which I think they likely accomplish by mixing 3 colors. I'll have to dig up the non-working one and take it apart to take a look.

    Cheers
    Al



  • @Sparkman said:

    I think they likely accomplish by mixing 3 colors

    That is how most if not all RGB LEDs work. Using PWM on the red, green and blue LEDs is how you achieve the different colors. I could probably have more than just the 2 colors if I can find a way to mix the 2 colors using PWM, but that might be a bit much for a nano to handle with all of the display multiplexing going on.


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