[time-nuts] Digital Mixing with a BeagleBone Black and D Flip Flop

Bob Camp kb8tq at n1k.org
Tue Oct 14 17:49:24 EDT 2014


Hi

Some of the “cheap" printed circuit board outfits  are now economical enough that they are a pretty good way to, go even for a fairly speculative breadboard type circuit. You wind up with a double sided board with a good ground. That significantly reduces the guesses and gotcha’s. There have been numerous threads here on the list about who likes which vendor and just how cheap is cheap. 

—————

One example of a gotcha - ground bounce may be responsible for the odd behavior when switching from the Q to the Q bar output on the flip flops. 

Bob

On Oct 14, 2014, at 12:34 PM, Simon Marsh <subscriptions at burble.com> wrote:

> Yes, I do understand I'm asking for trouble, though I kinda expected to see more noise rather than less.
> I guess its time to break out the soldering iron.
> 
> Cheers
> 
> 
> Simon
> 
> On 14/10/2014 17:22, Robert LaJeunesse wrote:
>> Using 74AC parts on what I think of as a pluggable breadboard (e.g. http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=2295705&MER=bn-me-ca-r1-best-sto-5) is asking for trouble. The parts are RF fast and the pluggable board has not very good contact resistance and certainly more inductance and shunt capacitance than is good for RF. I would highly recommend using dead-bug style on a solid copper plane, as provided by a chunk of unetched PCB material. (Jim Williams did a few like that, see http://1.bp.blogspot.com/-y3xQiBHHzaQ/UP3mLk96qWI/AAAAAAAAAss/ZvPbfN8lmTQ/s1600/eep114.jpg.) This approach allows for extremely short lead lengths and power supply bypassing (to the plane) with a near zero lead length capacitor.
>> 
>> Bob L.
>> 
>>> Sent: Tuesday, October 14, 2014 at 11:32 AM
>>> From: "Simon Marsh" <subscriptions at burble.com>
>>> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
>>> Subject: Re: [time-nuts] Digital Mixing with a BeagleBone Black and D Flip Flop
>>> 
>>> ... 74AC74 ... knocked up on some pluggable breadboard
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