Has anyone driven the 7-segment displays on the Cyclone III Development Board?

[Altera_Forum]

I have been trying to talk to the 4 digit 7-segment display on the Cyclone III development board. The Altera support guys refer me to similar projects using the Cyclone II but I think that development board uses a 2 digit (simpler) 7-seg display. Anyone got any experience of this?

[Altera_Forum]

You're right, cause other Dev Kits, e. g. Terasic DE-2 have non-multiplexed 7-Segment-Displays, while Cyclone III 3C120 board has a multiplex connection. So you need some logic (a clock divider and a multiplexer) to drive the display with meaningful data. 

 P.S.: I can show you a VHDL module for a similar purpose, that has 3x2x8 instead of a 4x8 multplexing scheme, including PWM brightness control. You should be able to adapt it to the said application.

[Altera_Forum]

I am driving the 7 segment LED, but it is so dim that one can hardly read it even in a dark room. And this is at 100% duty cycle. 

 User a multimeter, I see that the Cyclone III is driving the user LED at 1.8 volts. However, the 7-segment power LED is being driven at 2.5 volts. Even it is dim, but readable. When I try to change the VCCIO for the the user LED pins in the Pin Planner, it has no effect.    How do I change VCCIO for these pins?

[Altera_Forum]

Unfortunately, the real VCCIO is defined by the board wiring. The assigned IO standard is expected to match the voltage, but can't change it. I agree, that the circuit doesn't look well considered. You can sligthly increase the 7-segment display intensity by reducing the segment resistors from original 220 ohm to 47 or 22 ohm. According to the BOM, they are individual 0402 chip resistors.

[Altera_Forum]

Thanks for the quick response. I'm reading less than 1 mv across those 220 ohm current limiting resistors when the segment is on at 100% duty cycle. So even shorting them out would not may a difference (I wasn't looking forward to changing a bunch of 0402s). There is simply not enough voltage to drive these segments. 

 I thought that VCCIO was programmable?   Thomas

[Altera_Forum]

VCCIO is not programmable. see page 19: 

 http://www.altera.com/literature/hb/cyc3/cyc3_ciii51007.pdf

[Altera_Forum]

I realized, that the Dev. Kit uses a green LED display with a nominal forward voltage of 2.2V. It's absurd to operate it with a supply voltage of 1.8V (although I would expect a higher segment current than said 4.5 µA).

[Altera_Forum]

This today from Altera Support this is issue: 

 Hi Thomas   Thanks for the project file provided. Here we managed to duplicate the dim 7-segment LED issue.   Checking through the development kit details: I/O bank 8 has DDR2 SDRAM memory which use the 1.8 V SSTL signaling standard, unfortunately the 7-segment LED is in connected to I/O bank 8, it cause the 7-segment LED under power. Locating 7-segment LED in I/O bank 8 is due to insufficient I/O in EP3C120F780.   I sincerely regret that I could not better assist you regarding this issue due to some limitation. Sorry for any inconvenience. I sincerely hope that we may serve in more convenient way in the future. Thanks for using mySupport.   Best regards Ai Phing 

[Altera_Forum]

Hello, 

I am about to buy a Cyclone III Development Board and I might need to use the seven segment display.  Is there any update about the low voltage issue?   Francesco

[Altera_Forum]

I don't think there will ever be an update on this issue. It is a design problem, and it can't be fixed. 

If you absolutely need it, you could make an HSMC daughter board with the display. You can find a few prototyping boards for that purpose.