5 replies to this topic

[dwalker0229]

I've been doing computer programming for 32 years now so I know how to code in pretty much all the languages. I started with the C64 if anyone remembers that. So using VS is the easy part but now I'm working on the hardware. I took electronics back in highschool and understand the basics.

 

I've searched and came up short. Are there any ways to be able to use 31 4 digit or 110 1 digit 7 segment displays. I have 36 buttons hooked up using the matrix keypad driver so 12 pins are used up, A0-A5 and D0-D5. I have in hand for testing, a few max7219 and a few 74hc595. I have running, 2 4 digit displays on the spi(13, 11) and the latch set on 10. The first 595 runs all the segments and the other 595 switches each digit on and off. It works, I don't see shadowing. But how do I extend the 2 displays to 31? I think I'm going to run into problems with power consumption. I'm thinking I'm going to have to use an external power. Is that possible? how would they be wired?

 

Thank you.

 

[not4now]

Hello dwalwer!,

 

Here's a post that may help you a lot.

I think that you have heard about multiplexing, right?

 

http://forums.netdui...h-the-netduino/

 

Have a great day!

 

Not4Now

[dwalker0229]

Instead of the 595 I decided to use the 7219. If i can i'll use the as1107. But, is there a way to power all of them seperate from the netduino? I have a 5v plug i stripped and added a regulator, but how to introduce it into the system. ???

[dwalker0229]

Would the trasistor be my solution? If so how would i wire it? Do all pins on the 7219 get "transistor"ed? Or just the gnd and positive?

[nakchak]

You would definitely want to use an external PSU for that number of LED's.

Personally i would build the regulator circuit using a reference design for a 7805 or 7812 (depending on required voltage) regulator, then use that to power the displays and associated logic.

The only connections i would have to the ND would be to the data pins to set the right addresses on the multiplexer and display driver IC's.

I would also consider using some Opto isolators to protect the ND's data pins in case of short or something like that...

 

Hope those pointers help

 

Nak.

[dwalker0229]

Yes they do. Thank you not4now and nakchak.