AVR-Chat

Anyone have any pointers on the best way to run a 6 digit, 7-seg LED 
display from a atmega8?  Do I need to use transistors to multiplex?

--- In AVR-Chat@yahoogroups.com, "William Nachefski" 
<slaphappysamy@y...> wrote:
> Anyone have any pointers on the best way to run a 6 digit, 7-seg 
LED 
> display from a atmega8?  Do I need to use transistors to multiplex?

If you're working in DIP format, the Maxim MAX7219 is the easiest.  
SPI connection, and will control up to 8 7-seg displays, or 64 
discrete LEDs.

If you don't mind going SMD, then the MAX695x chips - there are 
several variants.  Both SPI and I2C for control, multiplexed, 
individual ports, input ports etc etc.  Very nice, simple to use.

They all have built-in fonts too, just send the char codes.

http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1339
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3195

Dean.

William Nachefski wrote:

>Anyone have any pointers on the best way to run a 6 digit, 7-seg LED 
>display from a atmega8?  Do I need to use transistors to multiplex?
>
>
> 
>
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I had a project that used 7-segment display some while ago, it was 
somekind of timer that turned on/off a light and displayed time to 
shutdown/power on, like min:sec on 7-seg. display. I have source code on 
this site http://users.volja.net/himba/countdown-timer02-25-03.zip it is 
written in C and could be compiled under linux, probably windows too, 
and avrgcc...
O, I used Maxim MAX7219 for driving LEDs

hope it helps

rgds, himba

On Fri, Jan 09, 2004 at 02:54:21PM +0100, himbA wrote:
> William Nachefski wrote:
> 
> >Anyone have any pointers on the best way to run a 6 digit, 7-seg LED 
> >display from a atmega8?  Do I need to use transistors to multiplex?

> I had a project that used 7-segment display some while ago, it was 
> somekind of timer that turned on/off a light and displayed time to 
> shutdown/power on, like min:sec on 7-seg. display. I have source code on 
> this site http://users.volja.net/himba/countdown-timer02-25-03.zip it is 
> written in C and could be compiled under linux, probably windows too, 
> and avrgcc...

> O, I used Maxim MAX7219 for driving LEDs

Is there a particular reason not to use the Mega8 to drive the display
directly? Are you short on I/O pins? Going up to a Mega16 gives you
more pins and other stuff as well.

-- 
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I did a couple projects with 7-seg LEDs on another processor, but I 
think what I learned was relevant.
I got eval units of the Max7219 and other LED driver chips. They are 
nice and self contained, but very expensive, >$10/each! Had I used 
those chips, it would have doubled the semiconductor cost of my board!

Ultimately, I chose to run it them using two shift registers. A 
SN74HC595 ($0.45) to drive the segments and a TPIC6B596 ($1.26) to 
strobe the common cathodes. Works great but requires processor 
overhead to drive the data continuously. For me, a little interrupt 
driven state machine did the trick. My board has an 8-digit display, 
four other 7-seg LED's and a bunch of status LED's driven by two sets 
of these shift registers. Additionally, I used the drivers to scan a 
key matrix giving me 56 inputs from pushbuttons and mechanical 
encoders. So with a little creativity, I had a large amount of I/O 
being run by $3.50 worth of shift registers that would otherwise have 
cost $21 using the stock LED drivers.

If you're just doing a one-off project, then the cost is 
inconsequential compared to the time involved. Plus, as noted, it does 
cost processor overhead to do it the way I did it.

-Ted
 
--- In AVR-Chat@yahoogroups.com, "fnatmed" <fnatmed@y...> wrote:
> --- In AVR-Chat@yahoogroups.com, "William Nachefski" 
> <slaphappysamy@y...> wrote:
> > Anyone have any pointers on the best way to run a 6 digit, 7-seg 
> LED 
> > display from a atmega8?  Do I need to use transistors to 
multiplex?

> 
> If you're working in DIP format, the Maxim MAX7219 is the easiest.  
> SPI connection, and will control up to 8 7-seg displays, or 64 
> discrete LEDs.
> 
> If you don't mind going SMD, then the MAX695x chips - there are 
> several variants.  Both SPI and I2C for control, multiplexed, 
> individual ports, input ports etc etc.  Very nice, simple to use.
> 
> They all have built-in fonts too, just send the char codes.
> 
> http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1339
> http://www.maxim-ic.com/quick_view2.cfm?qv_pk=3195
> 
> Dean.