OT: Help with Logic Dart AC adapter


I think there may be a few forum members who have access to the HP LogicDart logic probe instrument. I have one which I have recently been using extensively. I would like to ditch the battery mode of operation and go to an AC adapter. Apparently I have put my AC adapter (9100-5557)in such a safe location, that now I cannot find it. The LogicDart owners manual has no description or spec for the AC adapter. On the rear of the unit it states 12V at 0.1 amp , which seems quite reasonable. There is no mention of AC or DC. It is the diagram of the contacts that bothers me. This drawing indicates the center pin as a negative contact and the outer shell as the positive contact, which at least suggests a -12V DC supply which is not a conventional approach but possible. That is not something that I would expect.

I just don't want to connect -12V DC to the unit and accidentally damage the instrument. As far as I can determine HP never released a service manual for this device, therefore I do not know if it is reverse polarity protected. I suppose it is even possible that the device needs 12V AC. I just don't have enough information.

Does anyone on the forum have that AC adapter that they could measure and confirm the contact polarity? Does anyone have a LogicDart with that same diagram on the top rear?

Any information that anyone can provide is really appreciated.


I'm looking at a 9100-5557 right now. It is marked 12V DC 150 mA, tip (center) negative, ring (sleeve) positive.

The applied voltage isn't positive or negative; that has no meaning without a common reference. In other words, you don't have to find a -12VDC supply, as a +12VDC supply will work perfectly well. The requirement is simply that the tip be at a 12V lower potential than the ring. 0V tip and +12V ring would work fine, or -12V tip and 0V ring, or -6V tip and +6V ring.

Of course, this supply should be electrically isolated from the circuit you're testing with the LogicDart; with a wall wart this will generally be the case.



Thanks very much for the info. You have confirmed the diagram.

I understand, that of course, everything is relative to the reference, but I thought it odd that the center pin would be the reference. That is a little unconventional in my experience, but no reason why it should not work.

Now I can strap it to a bench supply and leave it running full time. I was getting annoyed by the automatic turn off after 5 minutes. I cancelled the turn off in system settings and of course 2 nights in a row forgot to tun it off manually. Now I can quit wasting batteries and just run it off a bench supply.

The information available from the members of this forum, once again, proves invaluable.



I wish the LogicDart had been more commercially successful, so that I could buy the new Agilent LogicDart II now.


Agreed. It is one of the handiest little gadgets I have ever owned. It would have been great to see it evolve over time. Somehow I got the impression it was not developed in house. I was always interested in the design of the unit but could never locate any schematics. I think that the $800.00 initial price was what killed it. At about half that it would have been wildly successful.


Actually it was developed in-house at HP, and some of the people involved were from the calculator division. Eric Vogel of HP gave a presentation to the Philadelphia club on June 5, 1997. Jake Schwartz has information and photos here.


Interesting| My assumption was based on the lack of documentation. Usually HP eventually releases documentation after an instrument became obsolete and the warranty period expired. Not so with this instrument. I just assumed they didn't possess the doc's. If they exist, I cannot find them. I may try to get that video.


In the 1990s HP moved toward keeping the innards of some test instruments secret, as had been done from the outset with calculators.


Hi Donald,

I am not sure if the Agilent page Logic Dart User's Guide can help you.


hpnut in Malaysia


Thanks for the info. I do have the manual but the manual gives no details on the AC adapter. Eric has provided the details I need so all is good.

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