1 Nov
2010
1 Nov
'10
11:23 a.m.
On Mon, Nov 1, 2010 at 3:10 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
On 2010 Oct 31, at 7:48 PM, Dan Roganti wrote:
oh yea, that would make it only 3chips - we have a winner !
Although the utliz.of the inverter chip is very low.
You could always just use a transistor.
I just didn't want to leave the '247 abandoned ;)
The on resistance of the 4066 (~80ohm) is way less than the 4016(~200ohm) -
which is why I chose that one - but marginally higher when operating a the
lower 5volts. But you could still compensate by lowering the LED resister to
keep it just as bright.
I never rule out CMOS :)
=Dan
--http://www.vintagecomputer.net/ragooman/
4 chip solution, 74247, 74138, 7407, 4066
No rule against using diodes ;)
http://www.vintagecomputer.net/ragooman/files/schematics/hexdec/hexdecoder1…
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).
