[sdiy] ripple counters

[Eric Brombaugh]

Roy J. Tellason - PLEASE NO CC! wrote:
> I didn't know there was still a need for 4164s out there (I have a lot of 
> them),  but I'm not sure what you're doing here.  They need two parts of the 
> address strobed in at two different times,  if I'm remember right.  And I'd 
> guess that the critical parameter here is how long before that clock the data 
> or address has to be stable,  or how long before that your counter is done 
> with any glitching it might be doing.
>   
The circuit he's talking about may be this one:

http://www.all-electric.com/b&c.html

Basically, it has a home-made 1st-order Sigma/Delta ADC generating a 
1-bit datastream that's stored in a 4164 DRAM configured as a 64k 
circular buffer. They use a pair of 'LS393s and a pair of 'LS157s to mux 
a 16-bit address down onto the 8 multiplexed address bits of the DRAM. 
The DRAM latches the address based on the RAS/CAS signals, so you need 
to ensure the counters are stable when those signals pop. I haven't 
looked closely at the control logic so I can't tell you if this 
constraint is met, but there are what appear to be caps hanging off of 
gate outputs, so it may be a tad hairy.

It's a pretty nifty idea and a great way to get a delay line without 
using BBDs. :)

I've been thinking about building something derived from this for a 
while. Those ancient 41XXX DRAMs are really cheap (less than a buck from 
Jameco) and it would be a hoot to see how well this works.

Eric