Author Topic: Signal Tracer/Injector Pen - The story  (Read 252 times)


Signal Tracer/Injector Pen - The story
« on: February 26, 2021, 12:51:40 PM »
I spent a lot of time on this last year and wrote a short story about it.

This is the story of how this handy tool came into existence.

Once upon a time there was a pedal builder soldering effect circuit after effect circuit.

Most of the builds were running out of the box – soldering finished, guitar to in – amp to out – there was noise!

But occassionaly there were effects that refused to work – even refused to get going after a serious amount of time staring at them or fumbling with the wires, looking at solder joints etc.

And there it is – there is this box. Its usually hidden in a cabinet but from time to time you take it out, look at it – put the piece of your most recent frustration into it – and put it back.

You know this box exists. Sometimes you dream about it. But you rarely open it up and take something out.

You know you are able to fix it. You know it will cost a significant amount of time looking at it and setting up the equipment for testing if you want to dig deeper into it.

So you usually let it go and this box will get filled to the brim with frustration.

I also have this box. Honestly when you are developing new pedals – like I do – this box is not only a box it becomes a cabinet itself.

I made some thoughts what it is that is hindering me to just pick something from time to time and fix it. I quickly came to the conclusion its the testing setup you need (signal generator, oscilloscope, multimeter, power supply, wiring…).

I am well aware that there already are quite a few testing rigs out there you can use. But I wanted something different.

I wanted something that is formed like a pen and that I can point and use like a soldering iron. And it should have the most needed features on board. I did not want any separate parts and pieces cluttering my workspace, just the power supply, the effect in question and the pen.
And I made it. It was a long way to go. There were six! (6) revisions from the initial design. Its my first SMD design and I had a steep learning curve and it took more than EUR 600,- and 9 month for this:

I wanted other people to use it as well, so it had to be cheap but great in design and usability. Here are the features:

  • Tracing of existing audio in a circuit – works as amplifier and loudspeaker
  • Signal generator feeds audio into circuit and tracer checks existence in circuit
  • Signal generator only – when the circuit is already plugged into an amp (not recommended)
  • Continuity tester

Another picture of all revisions that were made:

And the pile of prototypes that were produced during this development:

You want to know how to use it?

Here is a video I made. Its a little trashy but you will get the point

Check out the THcustom site to learn more (
« Last Edit: February 26, 2021, 12:59:12 PM by thofmann »
DIY-PCBs and projects:


Re: Signal Tracer/Injector Pen - The story
« Reply #1 on: February 27, 2021, 10:49:33 AM »
I watched the video yesterday, and I actually had a dream last night that I was using one of these pens (it worked very well in my dream, by the way).  A tool that lets me debug frustration-free in my sleep? Sign me up!  :icon_cool:

(Order placed)
"There is a pestilence upon this land. Nothing is sacred. Even those who arrange and design shrubberies are under considerable economic stress in this period in history." --Roger the Shrubber


Re: Signal Tracer/Injector Pen - The story
« Reply #2 on: February 27, 2021, 12:12:05 PM »
Yeah, thank you. 

The "debug during sleep" option is indeed included with the pen  ;)
DIY-PCBs and projects:

Marcos - Munky

Re: Signal Tracer/Injector Pen - The story
« Reply #3 on: February 28, 2021, 10:17:33 AM »
Very nice. I did a "tracing pen" with just a signal generator made out of 2 transistors, an LM386 amp and a notebook speaker. It's indeed a very helpful tool. And I'm sure yours is way better, since it have more features.


Re: Signal Tracer/Injector Pen - The story
« Reply #4 on: February 28, 2021, 03:17:30 PM »
i generally use my Atari Punk Console, my audio probe, and my tiny 3w amp i got for free with a 100 euro gutar.
its adequate, but i guess such a pen is better, not that i am in a financial position to get one, i just spend all the cash i had allocated for hobby use... maybe next month.

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