EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: HendriXML on January 08, 2019, 06:26:51 pm
-
Hi,
Here by my most useful project of 2019 yet.
It’s a bit quick and hot snot, but it has color-coded strain relieved silicone wires with pins which are very easy to handle.
Couldn’t find other examples on Google hence I post mine for inspirational purposes.
Bye
-
This is limited to low frequency, This thing will add noise and inductance to any fast thing
-
Doesn't work with the grounds, but so long as you're not bending the probes, you can take off the hook clip tip and just plug the pointy tip into most solderless breadboards. The length of those wires will add a lot of ringing to a fast signal, though, as they will act like antennae for other signals as mentioned.
-
User tggzzz's (here)'s web site entertaininghacks, has good stuff on the probe issue.
Also Bob Pease..
I bet you could improve that a lot while keeping the convenience aspect of it. Check out Bob Pease's low inductance probe holder ideas.
-
This is limited to low frequency, This thing will add noise and inductance to any fast thing
I know it has its limits, so does a breadboard :-+. Would thin shielded wires make it better suited for high frequency or does it really need 50 ohms (impedance?).
-
Hi HendriXML, i think we have a similar brain ;D
I posted this almost 3 years ago.
(https://www.eevblog.com/forum/testgear/scope-probes-gt-logic-hook-adapter/?action=dlattach;attach=214823)
With its limitations it is very usefull.
It was discussed here:
https://www.eevblog.com/forum/testgear/scope-probes-gt-logic-hook-adapter/msg914359/#msg914359 (https://www.eevblog.com/forum/testgear/scope-probes-gt-logic-hook-adapter/msg914359/#msg914359)
Mauro
-
Nice colors too!
On ali express those dupont cables come in a 20cm silicone variant to. i really like them.
-
Another user, tautech also posted this:
(https://www.eevblog.com/forum/index.php?action=dlattach;topic=55797.0;attach=174178;image)
Here:
https://www.eevblog.com/forum/beginners/life-hacks-for-the-beginning-ee/msg769430/#msg769430 (https://www.eevblog.com/forum/beginners/life-hacks-for-the-beginning-ee/msg769430/#msg769430)
And here:
https://www.eevblog.com/forum/repair/suggested-for-a-sticky-part-one-comments-or-additions-please/msg471163/#msg471163 (https://www.eevblog.com/forum/repair/suggested-for-a-sticky-part-one-comments-or-additions-please/msg471163/#msg471163)
Linked also because in thous threads there are some other nice hacks
Mauro
-
A breadboard is probably only good up to about 10MHz anyway, so I don't feel like these sorts of make-shift probe hacks represent a huge problem as breadboarding, almost by definition, means you aren't working w/ high speed signals.
For my use I made some even hackier solutions from some cheap and cheesy probe cables (https://www.aliexpress.com/item/1m-BNC-Male-Plug-to-Dual-Alligator-Clip-Oscilloscope-Testing-Lead-Cable-Probe-Electrical-Tool-Accessories/32813973391.html) that I terminated in dupont pins for quick probing of test points on projects being breadboarded. Both ends are color coded with heatshrink to match the scope trace colors:
(https://i.imgur.com/FiCIXS4l.jpg)
-
Doesn't work with the grounds, but so long as you're not bending the probes, you can take off the hook clip tip and just plug the pointy tip into most solderless breadboards. The length of those wires will add a lot of ringing to a fast signal, though, as they will act like antennae for other signals as mentioned.
That is some good advise, the tip is indeed thin enough.
I can support the probes by hanging them at my fumextracter, which embeds also my workspace light.
One inspirational aspect of this DIY extracter is, that it only turns on when the iron is taken of the stand. It is supported by a very sturdy monitor arm. So it is also easy to push it out of the way.
-
A breadboard is probably only good up to about 10MHz anyway, so I don't feel like these sorts of make-shift probe hacks represent a huge problem as breadboarding, almost by definition, means you aren't working w/ high speed signals.
For my use I made some even hackier solutions from some cheap and cheesy probe cables (https://www.aliexpress.com/item/1m-BNC-Male-Plug-to-Dual-Alligator-Clip-Oscilloscope-Testing-Lead-Cable-Probe-Electrical-Tool-Accessories/32813973391.html) that I terminated in dupont pins for quick probing of test points on projects being breadboarded. Both ends are color coded with heatshrink to match the scope trace colors:
(https://i.imgur.com/FiCIXS4l.jpg)
Very nice and cheap solution!
Would a signal generator be a good way to benchmark different cable solutions? I’m thinking of buying a better one. ( I have one at my low end Picoscope, which just has been made obsolete)
-
You should not use 50ohm coax cable for high impedance oscilloscope inputs. Probe cables use special high impedance (low distributed capacitance) coax with very thin wire.
If not, you are limited to very low frequency (<1MHz)
-
A breadboard is probably only good up to about 10MHz anyway, so I don't feel like these sorts of make-shift probe hacks represent a huge problem as breadboarding, almost by definition, means you aren't working w/ high speed signals.
For "digital" signals the only thing that matters is the risetime; the period is completely irrelevant.
If you want to think in anthromorphic terms, the wires don't know when the next transition is coming.
If you want to understand the theory, consider how to construct a square wave from harmonically related sine waves.
If you want a set of measurements, see https://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/
Then realise that modern jellybean logic can have 250ps transition times and harmonics into the GHz.
-
Hi, after one of the suggestions above I did visit your website. Very informative.
-
The solution from LUMA looks more practical. I use (for example) Pomona BNC(f) to grabber adaptors, which i modified with 0.64sq. or Mil #22D pins.
-
The things I realy like about my solution is that it only has one ground wire, so no mistakes there. And because the pcb lies stable on my desk, very light, thin and flexible cables move only a bit when probing, so my cluttered desk doesn’t get disturbed much :).
-
The things I realy like about my solution is that it only has one ground wire
That can, of course, also be a weakness when you consider the extra loop area and inductance. It depends on what you are trying to measure and ignore.
-
I’ve got a signal generator on order, so I will certainly do some experimenting later on. Better understanding of probing means also a better understanding of signal behavior in circuits I quess.
-
I like these. I would recommend the ones that use little bits of PCB be some how insulated and that you add a thing on them so the wires bend on a strain relief and it is linear rather then having a 90 degree bend on a floppy PCB.
A very nice option for a multimeter might be to get some pamona brand multimeter probe jacks and attach a pin to them, so they can be inserted into the PCB and the multimeter can be inserted into the probe jack.
those probe jacks are really really nice.
They have both banana cable jacks, and jacks that actually accept your multimeter's probe tip in a small collet <1mm.
similar & cheap https://www.amazon.com/Multimeter-Probe-Binding-Banana-Panel/dp/B0113IH0IW (https://www.amazon.com/Multimeter-Probe-Binding-Banana-Panel/dp/B0113IH0IW)
-
I’ve got a signal generator on order, so I will certainly do some experimenting later on. Better understanding of probing means also a better understanding of signal behavior in circuits I quess.
And your first experiment will lead you to question whether what you see on the screen is a function of:
- the scope
- the sig gen
- experimental technique, including probing
or all three :)
The specifications will be of paramount importance, particularly what they omit guaranteeing :( See my .sig about DACs.
-
My Siglent SAG1021 arrived and did some testing directly at its outputs, here are the (to my surprise) results at a 1 Mhz 4 VPP square wave:
- Using hookprobe and clip: obvious ringing
- Using probetip and gndspring attachment: no ringing
- Using hookprobe and clip via breadboard probing setup: obvious ringing
- Using probetip and gndspring attachment via breadboard probing setup: no ringing
So my conclusion would be for the moment: The probe clipwire introduces ringing. The breadboard probing setup also, but might be clear of ringing if clip isn't used in the the ground connection.
I don't understand it at all!
15 min later....., it seems that the ground clip/wire of my used probe isn't conducting at all! (Tested that) My other probes don't ring in any of the above conditions.
So the verdict is that this setup isn't to bad in respect to ringing.
-
My Siglent SAG1021 arrived and did some testing directly at its outputs, here are the (to my surprise) results at a 1 Mhz 4 VPP square wave:
...
I don't understand it at all!
15 min later....., it seems that the ground clip/wire of my used probe isn't conducting at all! (Tested that) My other probes don't ring in any of the above conditions.
So the verdict is that this setup isn't to bad in respect to ringing.
The 1MHz is completely irrelevant. What's the only important detail: the risetime/falltime?
For a little theory, see https://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/ (https://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/)
For more examples and theory, see https://www.analog.com/en/analog-dialogue/articles/hgh-speed-time-domain-measurements.html (https://www.analog.com/en/analog-dialogue/articles/hgh-speed-time-domain-measurements.html)
For more theory, which hasn't changed in the last 50 years (even if it is no longer taught), see http://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf (http://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf)
And for a justly famous application note, see http://www.linear.com/docs/4138 (http://www.linear.com/docs/4138)
-
In that respect I had the following results using the sync pulse of the generator:
- Probe with spring directly: 2 ns up 2 ns down
- Probe with spring via “breadboard probe pins”: 3 ns up 3 ns down
- Probe with hook via “breadboard probe pins”: 3.6 ns up 3.6 ns down
- Probe with hook direct: 3 ns up 3 ns down
- BNC cable Siglent: 2.6 ns up 2.2 down
- BNC cable 3 party: 12.2 ns up 10ns down
Conclusion: better than my 3 party BNC cable. And very near what I can measure with my scoop. Much better than my signal generator can do (23 ns) on square wave.
To my understanding I measured the capacitive properties of the setup this way? I should mention, because these rises where faster I saw a bit of ringing.
-
Photos of the experimental setup and scope screen would help; the devil is in the details.
I'd take a few digital pictures, reduce the resolution to 640*48 (or so!), and use the "+Attachments and other options" option when composing or modifying a posting.
-
Below are some screenshots. Because signal was very repetitive I used averaging mode.
Rise and fall changed with vertical range a bit, prop. because of the resolution.
-
Below are some screenshots. Because signal was very repetitive I used averaging mode.
Rise and fall changed with vertical range a bit, prop. because of the resolution.
The second trace shows the effect of the inductive ground leads. If you measure the period and know the probe tip capacitance, you can estimate that inductance. I'll bet it is around 0.8nH to 1nH per mm of lead length.
From the last two traces we can see that your cables are unterminated, and the driver cannot supply the necessary current to drive the cable. The 6ns and 12ns numbers aren't helpful and should be ignored.
-
From the last two traces we can see that your cables are unterminated, and the driver cannot supply the necessary current to drive the cable. The 6ns and 12ns numbers aren't helpful and should be ignored.
The first 2 measurements probed with the setting on 10x. The BNC cables lack such a mode so would’nt those pull more current?
Some scopes have a 50 ohm input capability would that be in this artificial situation better? Is it possible to add a normal 50 ohm resistor, or does it need to be combined with a capacitor/inductor, or is a good old fashioned bnc terminator on a T connector a possibility?
What would be the verdict on the probing method which started this thread? Any good?
-
From the last two traces we can see that your cables are unterminated, and the driver cannot supply the necessary current to drive the cable. The 6ns and 12ns numbers aren't helpful and should be ignored.
The first 2 measurements probed with the setting on 10x. The BNC cables lack such a mode so would’nt those pull more current?
You need to look up the theory of digital signals and transmission lines.
Your "high impedance *10" scope probe's input impedance is lower than a "low impedance Z0 resistive divider" scope probe. Work out the impedance of a 15pF capacitor at 100MHz.
Some scopes have a 50 ohm input capability would that be in this artificial situation better? Is it possible to add a normal 50 ohm resistor, or does it need to be combined with a capacitor/inductor, or is a good old fashioned bnc terminator on a T connector a possibility?
A proper 50ohm input is ideal, but they are only found in high end scopes (and Tek 485s). In other cases the 50ohms is simply a resistor added in parallel with the scope's high impedance input (i.e. 1Mohm//20pF).
Any L/C would only be 50ohms at one frequency; at all other frequencies there would be a mismatch.
The BNC terminator plus T connector will be 50ohms//20pF, where 20pF is the scope's input capacitance. It isn't too bad at these risetimes, but becomes more problematic at higher speeds.
What would be the verdict on the probing method which started this thread? Any good?
Look at your second graph.
-
From the last two traces we can see that your cables are unterminated, and the driver cannot supply the necessary current to drive the cable. The 6ns and 12ns numbers aren't helpful and should be ignored.
The first 2 measurements probed with the setting on 10x. The BNC cables lack such a mode so would’nt those pull more current?
Well yes but it depends on how the BNC cables are terminated as the SAG1021 is a 50 ohm source and expects to see a 50 ohm load for correct signal fidelity.
Some scopes have a 50 ohm input capability would that be in this artificial situation better? Is it possible to add a normal 50 ohm resistor, or does it need to be combined with a capacitor/inductor, or is a good old fashioned bnc terminator on a T connector a possibility?
Yes again but the source is 50 ohm and scope inputs, probe or BNC cabling all add capacitance to the load.
Have a look at this thread for example of correct scope connections for accurate reproduction of signal fidelity.
https://www.eevblog.com/forum/testgear/show-us-your-square-wave/ (https://www.eevblog.com/forum/testgear/show-us-your-square-wave/)
Most often we just want to check the type of signal in a circuit is correct and that should be enough to know if the circuit is working as it should but with the proviso that our probing technique could impact on signal fidelity.
If it does but we're aware it does we still have the result we looked for and can move on to examine further blocks in the circuit.
Just remember every measurement connection effects the measurement itself in some way. ;)
-
Okay I used a T splitter and a 50 Ohm Terminator I had lying around from the days of our coax LAN.
Now the signal looks better. But using that as a baseline of comparison is not OK I guess, it is a complete different situation than measuring with the breadboard probing thingy.
-
Okay I used a T splitter and a 50 Ohm Terminator I had lying around from the days of our coax LAN.
Now the signal looks better.
Yes but...........input attenuation setting is wrong. ;)
-
Okay I used a T splitter and a 50 Ohm Terminator I had lying around from the days of our coax LAN.
Now the signal looks better.
Yes but...........input attenuation setting is wrong. ;)
Depends on how you look at it, the signal generator (other scope screen) says it is outputting only half :). Oh I see, I still had 10x active. :palm:
-
https://www.eevblog.com/forum/testgear/show-us-your-square-wave/ (https://www.eevblog.com/forum/testgear/show-us-your-square-wave/)
I don't think those example are good to watch still being content with the SAG1021. It's like some judge says: your edges are kind of dull, it won't cut, surrender your weapon.
I'll wait a decade, so I can say. Yeah my old beasty has some good 1 Mhz square wave, very good in those days. And then everybody politely nods. :-DD
-
Here're the "squares" I manage to get with a Siglent SAG1021 and a Siglent SDS 1104E-E with a 50 Ohm T connection.
-
Here're the "squares" I manage to get with a Siglent SAG1021 and a Siglent SDS 1104E-E with a 50 Ohm T connection.
They show well-controlled outputs operating within their specification.
That's a different world to looking at general logic signals.
-
From the last two traces we can see that your cables are unterminated, and the driver cannot supply the necessary current to drive the cable. The 6ns and 12ns numbers aren't helpful and should be ignored.
The first 2 measurements probed with the setting on 10x. The BNC cables lack such a mode so would’nt those pull more current?
You need to look up the theory of digital signals and transmission lines.
Your "high impedance *10" scope probe's input impedance is lower than a "low impedance Z0 resistive divider" scope probe. Work out the impedance of a 15pF capacitor at 100MHz.
Some scopes have a 50 ohm input capability would that be in this artificial situation better? Is it possible to add a normal 50 ohm resistor, or does it need to be combined with a capacitor/inductor, or is a good old fashioned bnc terminator on a T connector a possibility?
A proper 50ohm input is ideal, but they are only found in high end scopes (and Tek 485s). In other cases the 50ohms is simply a resistor added in parallel with the scope's high impedance input (i.e. 1Mohm//20pF).
Any L/C would only be 50ohms at one frequency; at all other frequencies there would be a mismatch.
The BNC terminator plus T connector will be 50ohms//20pF, where 20pF is the scope's input capacitance. It isn't too bad at these risetimes, but becomes more problematic at higher speeds.
What would be the verdict on the probing method which started this thread? Any good?
Look at your second graph.
Okay my judgment would than be, if the transitions are faster than 3V / 50 nS ringing becomes more and more apparent on high impediance loads. Otherwise it will do just fine. I came to these values because at the rise an fall times of my sig. gen. it was stil (only) a bit noticable. In the analog domain thats is very usefull I guess.
In faster cases, normal probing with the clip lead is not advisable as well.
-
Here're the "squares" I manage to get with a Siglent SAG1021 and a Siglent SDS 1104E-E with a 50 Ohm T connection.
They show well-controlled outputs operating within their specification.
That's a different world to looking at general logic signals.
And it keeps the ringing away, so a nice combination with the breadbord probes. :-DMM
-
From the last two traces we can see that your cables are unterminated, and the driver cannot supply the necessary current to drive the cable. The 6ns and 12ns numbers aren't helpful and should be ignored.
The first 2 measurements probed with the setting on 10x. The BNC cables lack such a mode so would’nt those pull more current?
You need to look up the theory of digital signals and transmission lines.
Your "high impedance *10" scope probe's input impedance is lower than a "low impedance Z0 resistive divider" scope probe. Work out the impedance of a 15pF capacitor at 100MHz.
Some scopes have a 50 ohm input capability would that be in this artificial situation better? Is it possible to add a normal 50 ohm resistor, or does it need to be combined with a capacitor/inductor, or is a good old fashioned bnc terminator on a T connector a possibility?
A proper 50ohm input is ideal, but they are only found in high end scopes (and Tek 485s). In other cases the 50ohms is simply a resistor added in parallel with the scope's high impedance input (i.e. 1Mohm//20pF).
Any L/C would only be 50ohms at one frequency; at all other frequencies there would be a mismatch.
The BNC terminator plus T connector will be 50ohms//20pF, where 20pF is the scope's input capacitance. It isn't too bad at these risetimes, but becomes more problematic at higher speeds.
What would be the verdict on the probing method which started this thread? Any good?
Look at your second graph.
Okay my judgment would than be, if the transitions are faster than 3V / 50 nS ringing becomes more and more apparent on high impediance loads.
The problem is you don't have a high impedance load: the circuit "sees" a 15pF load - the probe tip capacitance.
If we use the rule-of-thumb BW=0.35/tr, then with tr=10ns BW=35MHz. I chose 10ns because that is typical of fast logic in the 1970s :) Today's jellybean logic is <1ns :)
Now consider the impedance of a capacitor, Z=1/2*pi*f*C, so 15pF -> 300ohms, and it gets lower at higher frequencies (e.g. 80ohms at 100MHz).
The "ringing" frequency will be f=1/2*pi*sqrt(LC), where C is the tip capacitance and L is the inductance of the ground connection, typically 90MHz for a 150mm ground lead.
Otherwise it will do just fine. I came to these values because at the rise an fall times of my sig. gen. it was stil (only) a bit noticable. In the analog domain thats is very usefull I guess.
In faster cases, normal probing with the clip lead is not advisable as well.
Whether or not it will "do fine" depends on the signal and output that you are probing. What might be fine for an AWG might not be "fine" for a logic signal.