Re: [avr-chat] ATmega88 + triple 7 Segment Display (CC)

[David Kelly]

On Tue, Mar 11, 2008 at 01:53:25AM -0700, Paul Lowe wrote:
> Here's one way to do it (thought up by a Comp. E. student who thinks
> he knows everything):
> 
> Otherwise, here is a solution using only one data port in parallel:
> 
> - Wire each 7 segment display to a digital 8 bit latch.
> - Use one data port to send your seven bits of segment data to all
> three seven segments via a bus

Thats complicating things unnecessarily.

[...]

> Or, if you can only use one pin for data transfer, get a SPI external
> register chip -- and map the output of that chip to seven output pins.

Thats more like it. Use one 74HC164 serial to parallel chip to drive
each display digit. Chain each HC164's Serial Out to the next's Serial
In. Then if you have two digits shift 16 bits out an SPI port, or
manually toggle the bits out a regular I/O port. After all your bits
have been shifted into place toggle the latch to move them to the chip's
outputs.

The HC164 is $0.50. A step up in display quality can be had with an
Allegro A6278 for $1.50, DigiKey P/N 620-1165-5-ND. The A6278 regulates
the current on each segment and only requires one resistor to set 8
output currents. With the HC164 you'll need 8 resistors.

I recently chained (9) A6278's and one HC165 (to read switch inputs) in
a successful design. Shifted in/out 80 bits each update.

-- 
David Kelly N4HHE, address@hidden
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Whom computers would destroy, they must first drive mad.