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?
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.
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?
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.
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
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).
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
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
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.