29 Nov
2009
29 Nov
'09
10:29 a.m.
On 29 Nov 2009, at 18:00, cctalk-request at classiccmp.org wrote:
Message: 2
Date: Sat, 28 Nov 2009 22:46:05 -0800
From: "Chuck Guzis" <cclist at sydex.com>
Subject: RE: Nand gate computer.
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Message-ID: <4B11A82D.20057.304D556 at cclist.sydex.com>
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On 28 Nov 2009 at 22:09, dwight elvey wrote:
Wire-OR is fine until you need to find out which signal is driving the input low, or
should I say to logic '1' (my machine uses -6.3v = logic 1, 0v = logic 0). You
need to isolate all the outputs to check them, not TOO hard on a wire wrapped machine but
must be a swine if you've soldered everything together. Of course there still the
other problem, if you need two or more wire-ORs from the same output, you need to buffer
the outputs separately or generate the signal two or more times.
I still like the 38s the best. Open collector
parts can do so much more than just a logic function.
The '12 is an OC 3-input NAND. I like 3-input gates better because
they lower the part count in circuits like J-K flip flops. If you
admit diodes to the mix, there's no reason that 38s or even 06s
wouldn't work just as well.
RTL and DTL were great when it came to wired-ORing. 
29 Nov
29 Nov
2:29 p.m.
----------------------------------------
---snip---
Wire-OR is fine until you need to find out which
signal is driving the input low, or should I say to logic '1' (my machine uses
-6.3v = logic 1, 0v = logic 0). You need to isolate all the outputs to check them, not TOO
hard on a wire wrapped machine but must be a swine if you've soldered everything
together. Of course there still the other problem, if you need two or more wire-ORs from
the same output, you need to buffer the outputs separately or generate the signal two or
more times.
HP had a clever probe that could actually measure the direction
of a few milliamperes on an IC lead. I use one of these
years ago while at Intel. I've not seen one since.
I suspect that it is because it still took an experienced
trouble shooter to actually use it effectively.
It didn't make a trouble shooter out of an idiot but
was a handy tool for a trouble shooter.
It did this by measuring the voltage drop but I suspect
that one could make a flux gate sensitive enough to detect
such a current.
Dwight
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3:05 p.m.
On Nov 29, 2009, at 5:29 PM, dwight elvey wrote:
I have an HP non-contact current tracer, looks like a logic probe,
was supplied in a pouch with a logic probe and pulser. It is
wonderful...tremendously handy. Is that the device you're talking
about?
-Dave
--
Dave McGuire
Port Charlotte, FL
Wire-OR is
fine until you need to find out which signal is driving
the input low, or should I say to logic '1' (my machine uses -6.3v
= logic 1, 0v = logic 0). You need to isolate all the outputs to
check them, not TOO hard on a wire wrapped machine but must be a
swine if you've soldered everything together. Of course there
still the other problem, if you need two or more wire-ORs from the
same output, you need to buffer the outputs separately or generate
the signal two or more times.
HP had a clever probe that could actually measure the direction
of a few milliamperes on an IC lead. I use one of these
years ago while at Intel. I've not seen one since.
I suspect that it is because it still took an experienced
trouble shooter to actually use it effectively.
It didn't make a trouble shooter out of an idiot but
was a handy tool for a trouble shooter.
It did this by measuring the voltage drop but I suspect
that one could make a flux gate sensitive enough to detect
such a current.
3:21 p.m.
----------------------------------------
From: mcguire at neurotica.com
I have an HP non-contact current tracer, looks like a logic probe,
was supplied in a pouch with a logic probe and pulser. It is
wonderful...tremendously handy. Is that the device you're talking
about?
-Dave
--
Dave McGuire
Port Charlotte, FL
Hi Dave
I don't think so. It was a completely passive.
It had 3 or four contact pins that were springy
so it could make contact.
I recall using it to find an input that was
shoulded to +5V.
Dwight
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3:43 p.m.
On Nov 29, 2009, at 6:21 PM, dwight elvey wrote:
Oh wow, completely different...I've never heard of anything like
that. I'd like to know more about them if you have any more info.
-Dave
--
Dave McGuire
Port Charlotte, FL
I have an HP
non-contact current tracer, looks like a logic probe,
was supplied in a pouch with a logic probe and pulser. It is
wonderful...tremendously handy. Is that the device you're talking
about?
I don't think so. It was a completely passive.
It had 3 or four contact pins that were springy
so it could make contact.
I recall using it to find an input that was
shoulded to +5V. 
30 Nov
30 Nov
1:13 p.m.
I have an HP non-contact current tracer, looks like
a logic probe,
was supplied in a pouch with a logic probe and pulser. It is
wonderful...tremendously handy. Is that the device you're talking
about?
That current probe is a toy I've always wanted, but I've never seen one
at a low enough price. I am told it's a great tool for finding shorted
inputs, etc.
-tony
5276
days inactive
5277
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5 comments
4 participants
participants (4)
-
ard＠p850ug1.demon.co.uk -
dkelvey＠hotmail.com -
mcguire＠neurotica.com -
roger.holmes＠microspot.co.uk