74hctxxx to 4000 series CMOS

[Kyle Jarger]

cyborg0 at GlobalEyes.net wrote:

> Is it ok to use a 74hctxxx series chip to go straight into a 4000 series
> cmos chip? 
> ...the demux suddenly cannot drive the leds that correspond with
> binary numbers 9-12, and all the leds beyond that eventually go out
> after a few seconds....

The TTL output may not be driving the high level voltage high enough 
to turn on the CMOS IC.  This might explain the weird behavior.

I think a pull up resistor of about 2K - 4.7K on each TTL output should 
pull the signal high enough.   Good Luck!

Regards,
Kyle Jarger
jkjelec at tiac.net
JKJ Electronics
Visit our MIDI/CV website http://www.tiac.net/users/jkjelec