I miss my Radio Shack Logic Probe...

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

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 :)

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"

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

martin

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.

--
 Thanks,
    - Win

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.

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

Yeah, same here. I haven't found the perfect replacement, but here's a pretty nice project:

(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.,

are also a pretty cool ideal; combining something like that into a logic probe would be a nice tool as well.

---Joel Kolstad

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 snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)