# Logic Probe

Great tool for debuging

I got a logic probe a while back but never got around to testing it. That was a mistake as it’s a brilliant tool for debugging your circuit. Until now I have used my trusty multimeter to check for signals when my circuit is faulty. But that’s a pain to have one eye on the multimeter display and one on the test point. With the logic probe it’s much easier, one sound (and LED) for a high signal, another one for low and a third for a puls train. If there is no sound the connection is either faulty, not connected or at high impedance.

So my tip is really to get yourself a logic probe, it’s worth every cent!

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What Chris said before  about using a micro controller and LCD instead of theold fassioned 555 timer makes a lot of sense these days where most robots have servos.

A small LCD displaying the pulse width in microseconds would be perfect not just for checking that a servo is receiving the correct signal but even for range finders since many that have an analog output also have a PWM output which the analog signal is derived from.

Electrical noise is always a big problem for robot builders. Programming the probe to look for pulse widths that are less than the minimum used by your code could be a good way to spot spikes. Monitoring the +5V line for voltage drops when motors or other heavy loads start up could also be useful.

Another function that can only be performed using a processor with an analog input is for determining the voltage level of a pulsed signal. Not only is it 3.3V or 5V. In some cases there might be a resistive load on your digital signal that pulls it up or down. By measuring the high level and low level of a digital pulse you can see if it is in the correct range.

I think Chris is right, these days you need a logic box, not a probe.

I am already finding uses for it.

So I just finished one built around a TL082 OpAmp. I just googled for a schematic and built one I had parts for. As I was working, I was thinking about how much more I could test with a microcontroller. Maybe a poor-poor-poor man's O-scope? Resistance, pulse length, high and low triggers of different sorts, timing events --all this could be done with a \$5 Arduino and a cheap LCD.

Oh! Oh! Holy Geeze!! I gots me a LCDuino fresh from Mr. McCabe! Oh, I think I might just have to make a "logic box"! Maybe a cool probe with a high/low led around the tip? Audio feedback? Oh! So many ideas!!

Thanks again, Mr. Andersen.

Mr. Andersen, hmmm...

They are very quick for debuging pulses ... as the better ones stretch the pulse so you have a better chance of seeing it....

Though i wish at least one of mine had a variable logic level detect, ie a slider pot you could set between say 0.5 and 4.5 volts , yes i know that there are 5V & 3.3 volt standards but this way you could at least workout what level your logic trips @.

Nice, thank you.

I have been meaning to get off my butt and make one of these. Now I will. Thanks!

Earlier ones where based off NE555 timers or a dual 556 timer to stretch incoming fast pulses......

....makes me wonder if a pic would be up for the job.

Hi Geir, Yes this is a very handy tool and I've been using it since a few years already. Thanks for sharing Sir :)

Thanks for the tip Geir. I will have to see if my local Electronics provider has these.