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  • Author Author: Jan Cumps
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DIY $10 Solder-in Oscilloscope Probe

Jan Cumps

It's sometimes hard to probe a point on a PCB.

Manufacturers sell "consumable" solder-in solutions.

You can temporarily or permanently attach them to your design, and it makes probing easier and reliable.

 

I have a suggestion for a DIY solder-in solution that takes little effort and is cheap + reusable:

 

image

 

Needed:

 

image

source: keysight

 

How to Make:

  • Cut one of the ground pins away
  • Take a short piece of black and red single strand wire (what you use on your breadboard). Remove a small end of isolation at both ends.
  • Tin all the ends.
  • Solder the red wire to the middle pin
  • Solder the Black wire to the remaining outside pin
  • Apply heat shrink to avoid shortcuts when the device rests on the PCB. Don't overdo it, so that you can remove it later when the wires are worn out.

 

How to use:

Solder the two wires to the desired component in the circuit.

Typically, you'll want to solder the black one to ground, the red one to the point of interest.

If you're careful, you can solder this in many times. If needed, cut away a little end of the wire and you are set for many future uses.

Insert the probe, without hook and crocodile wire attached.

 

Why?

  • Keeping probes fixed is difficult. Once you have 2 probes in your hand and have to adjust a button, you are in trouble.
  • If you keep the 2 wires short, this is a decent probing technique. Way better than the crocodile ground loop and hook.
  • It's so cheap that, when you are working long time on a design, you can leave this in your prototype.

  • Great idea

    I will have to put some of those connectors on my wish list.

    I would make some with Dupont pin sockets as well, so they could plug onto standard headers.

  • I've been trying recently to get a good connection for probing, without having to manually hold/adjust the probe.  I've found an alternative use for bootlace ferrulesbootlace ferrules (for 0.5mm2 wire.)  These fit well into PCB holes that are not yet populated by components or into actual PCB test pointsPCB test points (these are 1.1 - 1.3 eye diameter which I've found useful because I can hook-on, or use the probe tip with pigtail.)

     

    It's a good fit on the probe tip but loose on the pigtail

    image

     

    Once in the PCB test point though, a good connection is made due to the 'spring leverage' of the pig-tail - 'empty' test points are on the left of the image.  I hadn't thought until typing this that crimping the ferrule onto the pigtail may work well and is probably reversible so there may be mileage in trying that as well.  These can also be soldered into the eye without affecting the ability to hook-on.

    image

    Alternatively, I've found they work just as well dropped into a through-hole where the fluted opening makes good contact to the plating - these holes are prepped for a wire-to-board connector that I haven't fitted:

    image

    Again, the pig-tail springiness ensures a good connection.  The ferrules slide through and stop at the flare.

     

    Soldering the ferrule into a test point (instead of the eyelet test point) and leaving a 'stick' would allow the probe to both hook on, say for DC-coupled measurements, but also slide-in, for AC-coupled measurements. 

     

    It may not look like a good connection but trying with known signals shows it works well.  I have found that the test points on their own are great for hooking on, but don't make a great contact with the probe tip/tail on its own without a great deal of jiggery-pokery and holding breath so as not to disturb the connection was properly set up.  Incidentally, the test points are half the price from Farnell's CPC brand, at least in the UK.

  • That's a great idea and a lot better than dealing with springy pig-tails in confined locations.

  • Hi Jan,

     

    Great find! I didn't think of this idea - very neat! Also, it looks like it could be adapted to be soldered onto a nearby earth terminal using one of the sides, and then run a single wire, if the distance isn't far.

    By coincidence I was working a couple of nights ago to probe some stuff and really wished for solderable probes too. This was my attempt, it's still a work-in-progress. The yellow blob contains a 950 ohm resistor. I'll write it up once it is slightly more ruggedised implementation for anyone to assemble. It won't be as good as a normal probe of course, but sometimes a measurement is better than no measurement, at least to get some initial insight!

    image

  • in reply to ajcc

    I'm an Alan fan!

    I learned the techniques of DIY pitail winding and "make your own PCB inserts with wire"  from him.

     

    edit: from the video you show above.