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Altera_Forum
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16 years ago

driving seven segment user display

Hi.

I'm trying to drive the on board seven segment display on a Cyclone III development kit board EP3C120. The seven segment display is Lumex LDQ-M2212R1, quad digit.

I appreciate any advice ranging from digital design to verilog coding to fpga.

I'm picking up all these things in one go.

1. I did a counter to select all 4 digits one after another continuously as the display only has one digit selection at a time. I tried connecting straight from on board 50 MHz clock to clock of my counter design but compiling gave error of minimum pulse width. So I thought maybe I should feed the clock input to a megafunction PLL first then only to the counter. Is this the correct way of doing things?

2. I could drive one digit at a time (without clock) successfully but the digits lit up quite dimly as compared to the minus sign. It has to be relatively darker than a well lit up room for me to see the numbers lighting up. Is this typical of the seven segment display or am I doing something not right?

Thanks.

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Your 1:4 multiplex method seems basically correct. Typically, a kHz multiplex frequency would be used, generated by a synchronous counter. To achieve equal brightness of the minus sign, the duty cyle must be reduced. Unfortunately, the segment lines are driven from a 1.8V VCCIO without decreasing the current limiting resistors (could be considered a design flaw, to my opinion). Generally, for acceptable brightness, digit drivers with higher current capability than FPGA IOs would be needed.

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Thank you FvM.

    I'm inexperienced from both theory and hands on here. I am doing this seven segment driver for my self tutorials. I've been looking at it for all day and all night because I thought it didn't work. All I was trying to do was to drive all the 4 digits on the display with the same number controlled from the same DIP switches.

    Until I gave up and switched off the lights to my brightly lit room and saw that the 4 digits were actually displaying what it should but too dim for me to see!!. Dim displays, dim me, what a match!

    Now that I'm happy to go on, I cannot yet figure out how to feed the input with 4 different sets of codes having just 8 DIP switches. I'm sure there are ways for doing that with just my laptop and fpga board at home without needing external signal generators and ribbon cables?

    Thanks.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Hello to everybody.

    I want to use the same display on ciii board.

    Where can i find the datasheet on it?I've already tried to look at lumex.com, but it is quiet difficult to find it there.

    or what are the signals: an ca?

    thnaks a lot
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Display seems to be very-very dim.

    Datasheet on it says that max Forward Voltage is 2.6 V.

    The usual voltage for him is 1.8 V and if i set for example about 2.5 V?
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    That's a "design flaw" of this board !

    Already cost me hours too....

    The User 7-Seg is connected to a 1.8V VCCIO IO Bank.

    No chance to up the voltage to 2.5 V. (Hardwired, see board schematics).

    Just switch the lights off in the room....

    BTW: The Power 7-Seg on the same board is driven by the MAX II, which

    is configured with enough voltage. So this one is glowing brightly.