1 Nov
2010
1 Nov
'10
12:10 p.m.
On 2010 Oct 31, at 7:48 PM, Dan Roganti wrote:
4 chip solution, 74247, 74138, 7407, 4066
No rule against using diodes ;)
http://www.vintagecomputer.net/ragooman/files/schematics/hexdec/
hexdecoder1a.jpg
You have to take the ol' "ouside the box" approach.
I call it the Kobayashi Maru hack ;)
Since the '247 already provides 15 decodes already, I just tweak the
ouputs
for A-F
I use the lowercase 'c' since it saves a chip versus a uppercase 'C'
eh-hem, and don't let programmers design hardware :D
Neat suggestion to modify the existing A-F displays, but once you have
the '138 and a bunch of diodes you could just revert to the technique
of generating 8-F, and get by with 2 chips (247,138), 1 inverter (to
disable the 247 for >=8), and diodes.
The use of the 4066 does present a problem for direct drive of the
LEDs: ON resistance of the transmission gates is on the order of
hundreds of ohms (with considerable variability over devices and temp).