Maker Pro
Maker Pro

I miss my Radio Shack Logic Probe...

As a young teenager unable to afford fancy test equipment like a scope,
I came to rely on a $17 logic probe from Radio Shack. It's internal
pulse detection circuit was inadequate in that it could not
differentiate one edge from the other or from certain types of noise,
but I soon learned to wrap the lead of a diode around the probe point,
and probe with the other diode lead instead. This was of great use in
checking the output of things like memory strobes, address decoders,
etc.

Fast forward nearly 20 years and as an engineering professional I sit
surrounded by storage scopes with horrid user interfaces, ultra high
speed but unfortunately broken scope probes, etc... and wish I had that
now discontinued $17 gadget from the shack.

I see some logic probes in other test equipment catalogs. What's good?

- I want to detect steady high and low states, preferably audibly

- I want to detect edges, audibly

- preferably there would be no mode switching, or mode switching with
tactile state feedback

- needs to support 3.3v logic
 
M

martin griffith

Jan 1, 1970
0
On 3 Jan 2006 13:34:49 -0800, in sci.electronics.design
As a young teenager unable to afford fancy test equipment like a scope,
I came to rely on a $17 logic probe from Radio Shack. It's internal
pulse detection circuit was inadequate in that it could not
differentiate one edge from the other or from certain types of noise,
but I soon learned to wrap the lead of a diode around the probe point,
and probe with the other diode lead instead. This was of great use in
checking the output of things like memory strobes, address decoders,
etc.

Fast forward nearly 20 years and as an engineering professional I sit
surrounded by storage scopes with horrid user interfaces, ultra high
speed but unfortunately broken scope probes, etc... and wish I had that
now discontinued $17 gadget from the shack.

I see some logic probes in other test equipment catalogs. What's good?

- I want to detect steady high and low states, preferably audibly

- I want to detect edges, audibly

- preferably there would be no mode switching, or mode switching with
tactile state feedback

- needs to support 3.3v logic
Not quite what you want but Linear.com's AN70 page 39. I havent built
it but it looks good


martin
 
Not quite what you want but Linear.com's AN70 page 39. I havent built
it but it looks good

That looks like a nifty device, but it seems it's a sort of "ethereal"
scope trigger (field coupled). Something like that makes the
assumption that there's a frequent event worth triggering off of. If
there is, it might save twiddling knobs (or menus, ugh) on the scope.

But it doesn't really handle the case where there's not. For example,
I often need to go between probing state, vs probing for
single-instance events that happen when I do something like type a 10
keystroke command, or even click a mouse button on a GUI panel on a PC
interfaced to the device under test. A storage scope can handle both
of these tasks, but reaching over to flip it between trigger vs free
run modes gets very annoying - plus it would be much nicer to just have
the result audibly than have to shift eye focus from the IC pins to a
display and back.
 
I remember tracing out the circuitry in that thing many years ago. I
think it had a single 4001 gate and some discretes. Very simple
circuitry in any case.

Best regards,
Spehro Pefhany
 
D

DJ Delorie

Jan 1, 1970
0
I still have mine. Yes, it still works. No, you can't have it ;-)

The PCB contains only an LM339 and a dozen or two discretes.

The decal says "micronta digital logic probe"
 
D

David L. Jones

Jan 1, 1970
0
DJ said:
I still have mine. Yes, it still works. No, you can't have it ;-)

The PCB contains only an LM339 and a dozen or two discretes.

The decal says "micronta digital logic probe"

I've got two different Radio Shack model logic probes. Well, at least
the casing is different between them anyway. One was blue and square
the other was black and a bit sexier looking.
Haven't looked inside them since I was a kid, and haven't used one for
almost as long! They are still in the workshop somewhere....

You can still buy logic probe cases, so it's possible to make your own
nice looking one.

Dave :)
 
R

Robert

Jan 1, 1970
0
That looks like a nifty device, but it seems it's a sort of "ethereal"
scope trigger (field coupled). Something like that makes the
assumption that there's a frequent event worth triggering off of. If
there is, it might save twiddling knobs (or menus, ugh) on the scope.

But it doesn't really handle the case where there's not. For example,
I often need to go between probing state, vs probing for
single-instance events that happen when I do something like type a 10
keystroke command, or even click a mouse button on a GUI panel on a PC
interfaced to the device under test. A storage scope can handle both
of these tasks, but reaching over to flip it between trigger vs free
run modes gets very annoying - plus it would be much nicer to just have
the result audibly than have to shift eye focus from the IC pins to a
display and back.

When I google on "Micronta Logic Probe" [remove the quotes] I get several
used one offered at auctions on Ebay and Yahoo's auction sites.

Robert
 
W

Winfield Hill

Jan 1, 1970
0
[email protected] wrote...
That looks like a nifty device, but it seems it's a sort of
"ethereal" scope trigger (field coupled). Something like that
makes the assumption that there's a frequent event worth
triggering off of. If there is, it might save twiddling knobs
(or menus, ugh) on the scope.

The 4 pages describing Jim William's sniffer also appears in AN85,
page 20. The coil in his probe is specifed as a JW Miller #100267,
which is an 820uH inductor that must be one of the parts in Jim's
collection at home, because it appears in at least five of his App
Notes, performing different functions, usually a flyback inductor,
for example see the LT1073 datasheet page 16.


Unfortunately that's all we know about this part, because JW Miller
long ago discontinued it, and doesn't even show it in their cross-
reference search engine. I imagine it's a small axial-leaded part,
about the size of a 1/4-watt carbon-comp resistor.

..
.. 820uH _______________ termination
.. ,-####--)______________)---+----------------- scope
.. '-------' coax | | 4n7 1k ,---
.. | '--||-- pot --+
.. '-----------------'

Jim shows his sniffer with four to five feet of scope-probe cable,
which would have about 100pF of capacitance, and terminates it with
4700pF plus a 1k pot. 4.8nF would resonate with his 820uH inductor
at 80kHz, and a 413-ohm damper would set Q=1 to stop ringing. Jim
also shows a bit of ground lead with a clip, but it's not clear if
this is needed for proper operation, because the probe-coax shield
is already grounded at the scope end.
 
Winfield said:
The 4 pages describing Jim William's sniffer also appears in AN85,
page 20.
Jim
also shows a bit of ground lead with a clip, but it's not clear if
this is needed for proper operation, because the probe-coax shield
is already grounded at the scope end.

Based on one of the captions in AN70, I got the idea that the alligator
clip was to be mounted on a solid wire lead and used to physically
position the pickup probe in a suitable location.
 
J

Joel Kolstad

Jan 1, 1970
0
As a young teenager unable to afford fancy test equipment like a scope,
I came to rely on a $17 logic probe from Radio Shack..
Fast forward nearly 20 years and as an engineering professional I sit
surrounded by storage scopes with horrid user interfaces, ultra high
speed but unfortunately broken scope probes, etc... and wish I had that
now discontinued $17 gadget from the shack.

Yeah, same here. I haven't found the perfect replacement, but here's a pretty
nice project: http://members.cox.net/berniekm/super.html (he even used a Radio
Shack logic probe case!); the main deficiency relative to the original logic
probe is the lack of audio feedback, although one could certainly add that
without a lot of effort.

The Excelta Smart Tweezers (e.g.,
http://cgi.ebay.com/Smart-Tweezers-...ryZ25412QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)
are also a pretty cool ideal; combining something like that into a logic probe
would be a nice tool as well.

---Joel Kolstad
 
M

Mark Zenier

Jan 1, 1970
0
The 4 pages describing Jim William's sniffer also appears in AN85,
page 20. The coil in his probe is specifed as a JW Miller #100267,
which is an 820uH inductor that must be one of the parts in Jim's
collection at home, because it appears in at least five of his App
Notes, performing different functions, usually a flyback inductor,
for example see the LT1073 datasheet page 16.


Unfortunately that's all we know about this part, because JW Miller
long ago discontinued it, and doesn't even show it in their cross-
reference search engine. I imagine it's a small axial-leaded part,
about the size of a 1/4-watt carbon-comp resistor.

Dig, Dig, Dig...

It's a "Series L" molded choke
..9 inch long, .31 in diameter, axial leads

820 uH, 5 %, 22 ohm, 150 mA max.

Found it in a 1992 EEM and some of the series in a 1988 Arrow Catalog.
Must not have been too popular, they aren't around a couple of years
later. Nor the Series S, and M.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)
 
Top