I now see there were two of these Mullen boards.
(http://s100computers.com/Hardware%20Folder/Mullen/Extender%20Board/Extender%20Board.htm )
I actually have the first/early/simpler board. The later one looks more complicated and presumably better. Unfortunately I cannot locate its circuit.
Anybody?
John
Thanks, John.
Strange that it read OC outputs incorrectly, unless the load was not TTL level, or the pull-up was not strong enough.
Well, the circuit as I recall, used voltage dividers to set the Lo and Hi thresholds, with everything in between indicating open. The CMOS/TTL switch just put different resistors in the divider. If I were doing it, I would keep a similar circuit, but add a third option for variable threshold, then I could set it to whatever I needed it to be , even 3V logic levels. I probably have the schematic around here somewhere…I built it from a kit.
Bob Bell
Actually I have the Mullen probe, Bob. In the past on a few occasions, it miss read TTL signals on me. Forgot the details, but they were probably OC gates. May want to carefully check input settings if we go that route.
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Bob Bell
Sent: Thursday, January 29, 2015 1:55 PM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:6128] RFC - S100 Bus Test Point PCB
If you’re going to re-do the extender card with logic probe, I have a big suggestion:
Re-design the logic probe part so it uses analog comparators instead of the finicky digital threshold circuit. I have a Mullen Computer Products extender from years ago that uses analog comparators, and its rock solid and requires no adjustments or guessing. There is a switch for TTL or CMOS levels, and a pulse-stretcher for catching quick pulses along with the requisite hi, lo and open states. Further, the input impedance is like a megohm, so it doesn’t load the circuit.
I was thinking of doing such a re-design but you beat me to it. I’m just too busy right now building my second CPM system.
Bob Bell
John, I would be happy to take that on. I considered it before but didn't
want to molest someone else's design.
On 01/29/15 09:54 AM, John Monahan wrote:
Agree, let’s keep it simple. Popping it on top of the current extender board makes sense. Someday perhaps I, you, or somebody else, could reroute the traces on the current extender board (http://s100computers.com/My%20System%20Pages/Extender%20Board/Extender%20Board.htm ) , to add this very useful feature.
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Don Caprio
Sent: Thursday, January 29, 2015 8:51 AM
To: n8vem...@googlegroups.com
Subject: Re: [N8VEM-S100:6113] RFC - S100 Bus Test Point PCB
Guys, Great feedback so far and some great suggestions. I was trying to keep it
simply but some of the suggested features sounds like must haves. The +5v
at a minimum.
I was thinking that it would be used in a second extender card so all the other features
like LED's, power etc come from another source. Second extender card would sit in
front of the first with break out board so keeping the height to a minimum was important.
Sorry for the bad pic. That was just a screen grab from Kicad. Here's a better pic from FreeDFM:
<image001.jpg>
On Thu, Jan 29, 2015 at 8:27 AM, norwestrzh via N8VEM-S100 <n8vem...@googlegroups.com> wrote:
This looks like a great idea!! I'd take two of them if you fab. them.
Roger
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ilv...@gmail.com
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