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Altera_Forum
Honored Contributor I
995 Views

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.
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5 Replies
Altera_Forum
Honored Contributor I
75 Views

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
Honored Contributor I
75 Views

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
Honored Contributor I
75 Views

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
Honored Contributor I
75 Views

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
Honored Contributor I
75 Views

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.
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