Breadboard probing made easy - Page 1
Forum section: electronics / testgear

author: HendriXML
author_rank: Super Contributor
timestamp: January 08, 2019, 06:26:51 pm
content: 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

author: ebclr
author_rank: Super Contributor
timestamp: January 08, 2019, 06:48:58 pm
content: This is limited to low frequency, This thing will add noise and inductance to any fast thing

author: DaJMasta
author_rank: Super Contributor
timestamp: January 08, 2019, 06:53:12 pm
content: 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.

author: cdev
author_rank: Super Contributor
timestamp: January 08, 2019, 07:54:55 pm
content: 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 08, 2019, 08:05:42 pm
content: Quote from: ebclr on January 08, 2019, 06:48:58 pmI 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?).

author: mauroh
author_rank: Frequent Contributor
timestamp: January 08, 2019, 10:05:27 pm
content: Hi HendriXML, i think we have a similar brainI posted this almost 3 years ago.With its limitations it is very usefull.It was discussed here:https://www.eevblog.com/forum/testgear/scope-probes-gt-logic-hook-adapter/msg914359/#msg914359Mauro

author: HendriXML
author_rank: Super Contributor
timestamp: January 08, 2019, 10:28:36 pm
content: Nice colors too!On ali express those dupont cables come in a 20cm silicone variant to. i really like them.

author: mauroh
author_rank: Frequent Contributor
timestamp: January 08, 2019, 11:15:20 pm
content: Another user, tautech also posted this:Here:https://www.eevblog.com/forum/beginners/life-hacks-for-the-beginning-ee/msg769430/#msg769430And here:https://www.eevblog.com/forum/repair/suggested-for-a-sticky-part-one-comments-or-additions-please/msg471163/#msg471163Linked also because in thous threads there are some other nice hacksMauro

author: luma
author_rank: Regular Contributor
timestamp: January 09, 2019, 11:39:37 am
content: 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 somecheap and cheesy probe cablesthat 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:

author: HendriXML
author_rank: Super Contributor
timestamp: January 09, 2019, 12:26:43 pm
content: Quote from: DaJMasta on January 08, 2019, 06:53:12 pmThat 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 09, 2019, 12:34:01 pm
content: Quote from: luma on January 09, 2019, 11:39:37 amVery 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)

author: eb4fbz
author_rank: Regular Contributor
timestamp: January 09, 2019, 01:18:20 pm
content: 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)

author: tggzzz
author_rank: Super Contributor
timestamp: January 09, 2019, 03:00:36 pm
content: Quote from: luma on January 09, 2019, 11:39:37 amFor "digital" signals theonlything that matters is the risetime; the period iscompletelyirrelevant.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 wantaset of measurements, seehttps://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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 09, 2019, 04:57:55 pm
content: Hi, after one of the suggestions above I did visit your website. Very informative.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: January 11, 2019, 09:54:00 pm
content: 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 12, 2019, 02:19:54 am
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: January 12, 2019, 09:08:41 am
content: Quote from: HendriXML on January 12, 2019, 02:19:54 amThat 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 12, 2019, 11:05:48 am
content: 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.

author: coppercone2
author_rank: Super Contributor
timestamp: January 12, 2019, 11:15:11 am
content: 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 & cheaphttps://www.amazon.com/Multimeter-Probe-Binding-Banana-Panel/dp/B0113IH0IW

author: tggzzz
author_rank: Super Contributor
timestamp: January 12, 2019, 12:07:31 pm
content: Quote from: HendriXML on January 12, 2019, 11:05:48 amAnd your first experiment will lead you to question whether what you see on the screen is a function of:the scopethe sig genexperimental technique, including probingor all threeThe specifications will be of paramount importance, particularly what theyomitguaranteeingSee my .sig about DACs.

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 11:12:33 am
content: 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 ringingUsing probetip and gndspring attachment: no ringingUsing hookprobe and clip via breadboard probing setup: obvious ringingUsing probetip and gndspring attachment via breadboard probing setup: no ringingSo 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.

author: tggzzz
author_rank: Super Contributor
timestamp: January 21, 2019, 11:30:46 am
content: Quote from: HendriXML on January 21, 2019, 11:12:33 amThe 1MHz is completely irrelevant.What's theonlyimportant detail: the risetime/falltime?For a little theory, seehttps://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/For more examples and theory, seehttps://www.analog.com/en/analog-dialogue/articles/hgh-speed-time-domain-measurements.htmlFor more theory, which hasn't changed in the last 50 years (even if it is no longer taught), seehttp://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdfAnd for a justly famous application note, seehttp://www.linear.com/docs/4138

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 01:07:48 pm
content: In that respect I had the following results using the sync pulse of the generator:Probe with spring directly: 2 ns up 2 ns downProbe with spring via “breadboard probe pins”: 3 ns up 3 ns downProbe with hook via “breadboard probe pins”: 3.6 ns up 3.6 ns downProbe with hook direct: 3 ns up 3 ns downBNC cable Siglent: 2.6 ns up 2.2 downBNC cable 3 party: 12.2 ns up 10ns downConclusion: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: January 21, 2019, 01:49:27 pm
content: 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 04:12:18 pm
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: January 21, 2019, 06:54:22 pm
content: Quote from: HendriXML on January 21, 2019, 04:12:18 pmThe 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 07:28:35 pm
content: Quote from: tggzzz on January 21, 2019, 06:54:22 pmThe 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?

author: tggzzz
author_rank: Super Contributor
timestamp: January 21, 2019, 07:40:54 pm
content: Quote from: HendriXML on January 21, 2019, 07:28:35 pmYou need to look up the theory of digital signals and transmission lines.Your "high impedance *10" scope probe's input impedance islowerthan a "low impedance Z0 resistive divider" scope probe. Work out the impedance of a 15pF capacitor at 100MHz.QuoteA 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.QuoteLook at your second graph.

author: tautech
author_rank: Super Contributor
timestamp: January 21, 2019, 08:01:37 pm
content: Quote from: HendriXML on January 21, 2019, 07:28:35 pmWell 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.QuoteYes 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/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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 08:38:40 pm
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: January 21, 2019, 08:42:02 pm
content: Quote from: HendriXML on January 21, 2019, 08:38:40 pmYes but...........input attenuation setting is wrong.

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 08:50:19 pm
content: Quote from: tautech on January 21, 2019, 08:42:02 pmDepends 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 21, 2019, 09:07:50 pm
content: Quote from: tautech on January 21, 2019, 08:01:37 pmI 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 22, 2019, 08:28:25 am
content: Here're the "squares" I manage to get with a Siglent SAG1021 and a Siglent SDS 1104E-E with a 50 Ohm T connection.

author: tggzzz
author_rank: Super Contributor
timestamp: January 22, 2019, 09:20:05 am
content: Quote from: HendriXML on January 22, 2019, 08:28:25 amThey show well-controlled outputs operating within their specification.That's a different world to looking at general logic signals.

author: HendriXML
author_rank: Super Contributor
timestamp: January 23, 2019, 01:32:37 pm
content: Quote from: tggzzz on January 21, 2019, 07:40:54 pmOkay 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.

author: HendriXML
author_rank: Super Contributor
timestamp: January 23, 2019, 01:42:00 pm
content: Quote from: tggzzz on January 22, 2019, 09:20:05 amAnd it keeps the ringing away, so a nice combination with the breadbord probes.

author: tggzzz
author_rank: Super Contributor
timestamp: January 23, 2019, 01:58:21 pm
content: Quote from: HendriXML on January 23, 2019, 01:32:37 pmThe problem is youdon'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 1970sToday's jellybean logic is <1nsNow 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.QuoteWhether 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.