AVR-Chat

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.