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Signal Tracer (Old school)

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One of my projects for this year is to create a "new age" signal tracer like I used when i was a kid.

What I had was an old heathkit IT-12 pictured below.

image

 

The thing is i have no clue how this worked. I loved using it, and well just playing with it. It was sencitive efuff to hear audio runing through circuts without contacting the circuts, just getting the tip close to a trace.

 

So to start things off I created a audio amplifyer circut that I think is how this unit worked.

image

There are 2 things that I am compleetly lost about though.

 

  1. How to make, or what to use for the probe.
  2. How to make the visual circut.

1~I was thinking of taking a nail, and wraping copper wire around the nail to create a pickup coil, but i have no idea if this would work or if there is something better to try.

I am open to any ideas.

 

2~I was thinking of a 10 segment led bargraph desplay. But where would I need to conect the driver up to in the circut in the diagram? Would it be the the + side of C5?

I ordered some LM358N LM358 358 Low Power Dual Op-Amp IC's for this project that should be here on the 10th.

So I am planning on bread boarding this after that.

 

Also, I was thinking about starting to documenting some of my projects by video maby. So this might be one of the first ones I may try to document.

I have been feeling inspired by @Peter Oakes.

  • in reply to jc2048

    I see what you mean for the pot,I  was using it as a over voltage trim, but I can simply place a zener diode in place instead.

     

    On a sim it works fine, but, we will never know until I get something in a breadboard.

    And I am waiting on a new scope, and camera to come in before I can start testing it up.

  • in reply to jc2048

    Hi Jon,

     

    Exactly as you say, it would be good to build that into a small screened handheld enclosure (the FET part, if not the entire circuit), with a cable down to the battery box/speaker/LM386.

     

    Basically just a tiny length of coax with solid conductor, to extend slightly away from the enclosure (a mint box, or perhaps a painted cigar tube!). The solid conductor being filed to a tip.

     

    Incidentally for an unrelated project I built this a while back.. severe overkill for a low-cost audio probe of course, I'm not suggesting it. 

    This will have a few pF capacitance too, but I'd only intended to use it at low frequencies for some other project. The part on the right is

    just an SMA shell, to use as a cover to protect the tip when not in use.

    image