simple and effective, but I’d think a bicolor led would cost less than the 7-seg. The 7805 will probably drain the 9v batt in no time and get hot doing it.

Posted at 7:28 pm on Jun 27th, 2008 by Batman

So basically, whoever created this has managed to take a device that can be built with an led, 2 resistors, a transistor, and a battery, and created a version thats larger, costs more, is more labor intensive to build, and offers exactly the same functionality.

Am I missing something?

Posted at 9:58 pm on Jun 27th, 2008 by wolf

NIce little project you have put together.Thanks, regards Colin

Posted at 10:48 pm on Jun 27th, 2008 by Colin

Perhaps I got the wrong vibe by the end of the synopsis. “Of course, the resulting device is not as versatile as a LogicPort logic analyzer, but it is still useful.”

I’ve owned the logic analyzer from intronix for a few years. I also own a micronta logic probe, HP Logic Dart, and a Fluke 123 scope meter. Each has its own. And to give the logic probes a little more respect. All these tools are great for their intention. But a logic probe has a place too. The logic analyzer, Logic Dart and Scopemeter take far too long to setup for most quickies. A logic probe gets powered and references signals. visual and audible indications are great and there is not setup over head. I once repaired a pinball controll board using only a logic probe- This was the eye opener that each tool does infact have a very special place in terms of use. Within 5 mins the pinball machine was working. It would have taken that long to setup the other instruments consider the broad range of pins and various signals that needed to be checked.

Don’t take this the wrong way either. The logic port is an excellent tool. But it should not be compared to a logic probe. Apples and Oranges anyone?

Posted at 12:50 am on Jun 28th, 2008 by Steve

amazing that they did it all without any syringes!

Posted at 12:57 am on Jun 28th, 2008 by chr0n1c

@Wolf (post 3)

Would you mind sharing how those few components make a working logic probe? I had a google and only came up with IC based designs :(

Ty!

Posted at 12:50 pm on Jun 28th, 2008 by Dennis

A 9V battery to 7805 linear regulator is a really bad idea. It will burn that extra 4V off as heat and it will constantly leak about 2-3ma of current. You’ll be replacing that battery a lot. Find a LDO regulator with a low Iq (quiescent current).

Posted at 1:24 pm on Jun 28th, 2008 by adam

@dennis

Basically, you just connect the emitter of a common npn transistor (like a pn2222a) to the probe batteries ground, connect an led and a current limiting resistor in series between the transistors collector and the batteries positive terminal (with the led’s plus side attached to the battery), then attach a second, high value resistor between the transistors base and the logic probe.

The resistor values will depend on the voltage your probes running on, and the voltage you want it to detect, but for a 9v battery and signals above 2v a 470ohm current limiting resistor, and 20k probe would put the max current through the led at 19ma, and keep the current through the probe to less than 1ma. If you wanted to, you could probably go with even higher resistance on the probe and still keep the transistor saturated, but the highest my pot goes is 20k.

If anyone sees that I’m mistaken on any of this feel free to correct me.

Posted at 5:23 pm on Jun 28th, 2008 by Wolf

Thankyou wolf! Ill give that a go :)

Posted at 4:29 pm on Jun 29th, 2008 by dennis123123

Thoughtful post and well written. Please write more on this if you have time.

Posted at 4:59 pm on Jul 3rd, 2009 by Becky

This is WAY too complicated and power-hungry for a logic probe with this level of functionality.

Posted at 11:41 am on Aug 14th, 2009 by NOBAMA