On 2012 Mar 5, at 12:41 PM, Eric Smith wrote:
Ethan Dicks wrote about the COSMAC Elf:
To guess, I know of one common issue with
hand-made 1802 designs -
the 4016 and 4066 are not 100% interchangable. They have different
switch response characteristics. ISTR the older designs used 4016
switches which are harder to find now than 4066 switches.
It's certainly true
that the 4016 and 4066 have differences in
their characteristics. However, in the simple way in which it is
used in the Elf, I can't see how it would make any difference. I
can't say that I've actually tried it, though.
If not that, then the other issue to investigate
is to ensure that
the input button is debounced
Yes, that is quite important.
The basic design does provide debouncing, as I'm sure you are aware
(although how it is achieved might be considered either cute or
questionable, depending upon one's attitude to design).
I wondered why they bothered to debounce the nCLEAR and nWAIT lines
when they are level-sensing rather than edge-triggerred, but I
haven't really examined the details of the 1802 functioning in depth.