connecting a 4digit 7segment display

Anything about FPGA boards, like how to assemble SMD components, find low-voltage regulators, FPGA configuration...

connecting a 4digit 7segment display

Postby itx » Thu May 20, 2010 5:19 pm

hey there.
could somebody please tell me the idea, of connecting a 7 segment display? Or rather, controlling it.

I have a common anode 4 digit display. From what i understand (lets talk about just one digit for now):
Pin1 connects to "base" of a npn tranzistor. the "collector" connects to 3.3v rail, and the "emitter" goes to the anode. then 7 cathodes connect to 7 other pins. lets say pin11 through pin 17. (there are resistors on the cathodes, and on the base)

Now in order to display a digit, i have to send a logic "1" to pin1, and somehow enable ground on some pins11-17 . is this correct?

if so, in Quartus II, I simply select pin1 as an output pin, but what am i supposed to do with pin11-pin17 ? Can somebody please explain this to me?

I hope I explained it in an understandable way




here is a shabby diagram (i forgot to draw the resistors)
Image
itx
 
Posts: 8
Joined: Sat Nov 21, 2009 2:58 pm

Postby WadeH » Thu May 20, 2010 11:18 pm

You seem to have it figured out, though I don't see the need for the transistor.
If you have, say, 270ohm resistors in series with the LEDs, they will only pull about 5mA each and not need a transistor.
If you are planning to use the transistor to multiplex digits, the objection is retracted.

The LEDs could also be lit by sending the output pins HIGH: just return them to ground.
WadeH
 
Posts: 13
Joined: Fri Apr 22, 2005 3:17 pm

Postby itx » Fri May 21, 2010 6:12 am

but I still don't really understand how to control pins 11 - 17.

If I simply set them as "output", it would mean that they will have positive voltage output. Thats not really what I want. Or is it?

Pin1 has to be a '1' , or HIGH, and pin11 has to be connected to ground and toggled on demand. Thats the part that I don't know how to do :)

I'm using alteras Quartus II
itx
 
Posts: 8
Joined: Sat Nov 21, 2009 2:58 pm

Postby WadeH » Fri May 21, 2010 3:19 pm

There is very good information here:http://www.fpga4fun.com/Opto.html
WadeH
 
Posts: 13
Joined: Fri Apr 22, 2005 3:17 pm


Return to General boards

Who is online

Users browsing this forum: No registered users and 2 guests