Need help with some measurements.

Hi John,

I'll measure up several later today, and post the results.

Also, have you considered making the entire 'scope probe? There could perhaps be interest in that.. I'd be interested : )

There is a brief comment mentioned in 'Art of Electronics' where the profs just use co-ax cable (RG178 in their case) and attach a 953 ohm resistor in series on the end, and it becomes the probe. This then is a X20 probe (and it expects the 'scope end to be set to 50 ohms, or use a T-piece and a 50 ohm terminator for 'scopes that don't have that built-in. This would be good for up to 100-200MHz perhaps, covering many use-cases.. It is mentioned here, in a yellow box:

https://electronics.stackexchange.com/questions/351368/high-speed-passive-probe-contradiction-between-authors-or-differe…

Trouble is, a resistor is too flimsy for general probing. Maybe it would be nice to have a complete probe with the co-ax, resistor, and your probe attached.

Hi Shabaz,

I haven't considered it as I felt that there needed to be physical tuning that I wasn't capable of. My partner in the Non-Slip probe adventure Neil asked me today about making Oscilloscope probes and so I thought that perhaps I could make adapter tips for probes that would not be a problem at lower frequencies. That is what got this inquiry started. I have gotten so spoiled using the meter non-slip probes that every time I use my oscilloscope probe I get real frustrated with keeping the probe point where I want it. Since I am pretty much a low frequency tech I decided to make a set of adapter tips for my scopes. When I found the probes had different diameter pins I suspected that there wasn't  a standard size like there is for the meter probes. Now I am collecting data just to see how bad the dis-uniformity really is.

John

jw0752, for low frequencies, I use a converter, and then normal DMM probes with your anti-slip points.

When you build add-ons for oscilloscope probes, there's a whatch out apart from different size of probes:

the tips are delicate, so the insertion power has to be low and the grip power high enough so that the extension does't cause stress on the probe point.

Hi John,

I think you're right, some tuning at the probe end may be needed for high frequencies. I think maybe it would be adequate for 100-200MHz with no tweaks, but I've not attempted it. I've been meaning to try it for ages, I bought the 953 ohm resistor in a couple of sizes and suitable coax/connector a while back. I'll give it a shot in the next week or two, perhaps that could be engineered into a product with your probe on the end, if you can find a way to construct it.

Plus, using the 50 ohm termination means no need for any tuning at the 'scope connector end at all.

Hi Jan,

I think that you have the right approach. So far everything about building adapters specific for scope probes looks problematic. Your point about stress on the existing probe tip is well taken. Tips that are 4 mm long and 1 mm wide do not provide sufficient support structure for addition of a potential lever arm in the form of an adapter. I must get myself one of those adapters.

John

Hi Shabaz,

I look forward to the results of your build.

John

w2aew - a field engineer of Tektronix - has made nice videos on (among other interesting subjects)  probing techniques.

I use this one at times when direct probing with the pig tail ground is not enough or not practical:

Edit media

Dimensions x Small Medium Large Custom

Subject (required) Brief Description Tags (separated by comma) Video visibility in search results Visible Hidden

Parent content

RE: Need help with some measurements. Comment on DIY $10 Solder-in Oscilloscope Probe

Poster

Upload Preview

Ok

Cancel

w2aew - a field engineer of Tektronix - has made nice videos on (among other interesting subjects)  probing techniques.

I use this one at times when direct probing with the pig tail ground is not enough or not practical:

Edit media

Dimensions x Small Medium Large Custom

Subject (required) Brief Description Tags (separated by comma) Video visibility in search results Visible Hidden

Parent content

RE: Need help with some measurements. Comment on DIY $10 Solder-in Oscilloscope Probe

Poster

Upload Preview

Ok

Cancel

Hi Jan,

Thanks for the video. It is an excellent idea and I am sure it will be of utility. I will do some experimenting with it tonight.

John

Hi Jan,

I had all day to think about the ideas that were in the video so by this evening I was ready to try some things to see if I could come up with an Oscilloscope Probe adapter based on the coiled wire technology. I began by rolling some wire around different size drill bits. It took me 4 tries to get the size that I needed. I am using 16 Ga Brass wire for the outer ground.

As you can see I have continued the coil quite a ways past the ground ring on the probe. While the added length will add some shielding the main purpose it to provide support for the central connection to the probes tip. The small coil is the one that will go onto the probe tip. Both outer and inner coils are wound with a right handed twist so that when one goes to put the adapter on the probe a right hand twist will cause the coils of the brass to open up. Likewise a right handed twist will be needed to remove the adapter. A left handed twist of the adapter will tighten the coils and lock the adapter more securely in place.

The next challenge was to attach the small coil to the brass non-slip point holder without filling the coil with solder. Brass has a pretty good affinity for solder and it would easily wick into the coil. Here is a picture of the process of soldering the coil to the brass tip holder. The second pictures shows the completed central assembly of the adapter.

The next step was to heat shrink enough layers on this central shaft that it sizes out to fit into the outer ground coil.

The outer coil of wire is fitted over the now heat shrink covered inner shaft.

By removing the center shaft and lightly coating it with epoxy and reinserting it into the coil we can get the two pieces epoxied together and not allow the glue to get back to the contact area of the probe. A thin layer of epoxy is also spread on the front section of the outer coil but not back as far as the part that slips onto the oscilloscopes ground ring. Finally a piece of heat shrink is installed over the entire assemble and then we wait for the epoxy to cure.

Here is the finished adapter with the non-slip point attached. Once the glue sets I will apply a right handed twist and if I have been lucky and no glue has seeped where it wasn't wanted I should be able to remove and reinstall the adapter as needed. If on the other hand the glue got away from me then I may have a permanent non-slip tip on this probe.

Thank you again for finding that video and inspiring my fun this evening.

John

Hi Jan,

The glue has set and the adapter came off as hoped.

Here is a picture looking into the back of the adapter.

While this has been a successful build for me it still will not make the production of a standard adapter possible as the dimensions of the different probes are not compatible. I do like the sturdiness of the adapter compared to the ones I did yesterday that were only supported by the 1 mm oscilloscope probe tip. I will just have to keep thinking.

John

I wonder if the coiled spring has enough "give" in it that another 0.1-0.2mm of probe tip diameter wouldn't matter too much? Furthermore, as some tips are somewhat angled, for those maybe making contact isn't as difficult.

Perhaps you could slip the adapter on another probe of yours and let us know how it works/doesn't work.

- Gough

Hi Gough,

The brass wire that I used doesn't have much elasticity and the center coil itself is even worse due to its small diameter. I had hoped to have something like the spring inside a wire nut but in the end it is sized very close to the 1 mm tip on this particular probe. I will check things out tomorrow and if possible I will see if it will work with my other probe set. Thanks for checking it out.

John

Interesting to see the insides.

I'm wondering now that you've provided the support with the ground that you could utilise something else for the probe inner contact.

They are usually high impedance so the contact resistance isn't as important as a high current connector.

It would be interesting to see how the clip end attaches ... if someone has a dead/broken version.

I have a couple of different versions of probes but haven't had time to get the calipers out ...sorry

Mark