DIY Differential probe again again - please help :-) - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 03:37:51 am
content: I have now read several super long treads about the subject on this great forum, but I simply need some help to know how to start and to find something that do work. There is a lot of ideas and discussions and diagrams all over but it always end up s an great start but never usable or something else that stop the project in it's tracks.What I am hoping fore is a "between" board that I can couple between my scope and my standard probe.500MHz no need for over 65VThe image is from this site where all components are listed but you have to pay for the article:https://www.elektormagazine.com/magazine/elektor-201409/27026I have found this article:http://blog.weinigel.se/2016/02/26/ghz-differential-probe.htmlAnd this wary long spec sheet for the THS3201 amplifier:https://www.farnell.com/datasheets/1447056.pdf

author: ogden
author_rank: Super Contributor
timestamp: October 05, 2019, 05:58:52 am
content: Quote from: FriedMule on October 05, 2019, 03:37:51 amThis is low ~60KHz bandwidth probe isolation adapter.

author: MosherIV
author_rank: Super Contributor
timestamp: October 05, 2019, 08:44:05 am
content: A simple free approach (depends on scope) to differential probing is toUse 2 channels on the scopeDO NOT use the ground clamp of the scope probes.Use the math function of scope, subtract 1 channel from another.Use one probe on one measurement pointUse the probe on the other measurement point.The math function act like a differential function between 2 channels.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 10:39:28 am
content: Quote from: ogden on October 05, 2019, 05:58:52 amOkay, thanks. I could not find that out just by looking at the image or components. If that had been a 500MHz would that have been enough? I mean, if all I want is to be able to measure where there is different grounds.What about the second link, is that a usable design?Quote from: MosherIV on October 05, 2019, 08:44:05 amYes fine little trick but it have to be possible to build a probe instead of having to buy a probe or reducing my scope to half of the channels?

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 02:35:04 pm
content: Is it posible to make this Differential probe:http://blog.weinigel.se/2016/02/26/ghz-differential-probe.htmlto be able to handle about 65V?

author: ogden
author_rank: Super Contributor
timestamp: October 05, 2019, 04:24:47 pm
content: Quote from: FriedMule on October 05, 2019, 02:35:04 pmYes indeed. Voltage divider at the input needed and maybe some circuit for offset error trimming needed.Note that schematics of final revision of that probe is not published. Github comment contains info about final modification which were done to achieve said performance which is great especially considering BOM cost of that thing.Quote from: FriedMule on October 05, 2019, 10:39:28 amMain component is isolation amplifier, AMC1200. Bandwidth is specified in the datasheet:http://www.ti.com/lit/ds/symlink/amc1200.pdfQuoteEven 10KHz BW probes have their use. What is your application that you are looking for 500MHz BW? What scope do you have, what is bandwidth of it?

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 06:58:12 pm
content: Quote from: ogden on October 05, 2019, 04:24:47 pmI am currently trying to play with this circuit, and hope tinker with related projects:-)http://www.foxdelta.com/projects/pm1.htmThe reason for the voltage is that I hope to use it for more then just that one project, and I know I will work with projects in the 60V rangeSo a probe where I can just probe when I need to, and not have to build an other later for that voltage.May I ask if you please could guide / draw something that could be used to allow 65V?

author: ogden
author_rank: Super Contributor
timestamp: October 05, 2019, 07:20:50 pm
content: Quote from: FriedMule on October 05, 2019, 06:58:12 pmIndeed you may ask. I already did tell you - you need voltage divider. You may skip offset trimming at the beginning. Question "could you give me solution on silver plate" is one I would simply answer "definitely no". So please do your research and ask good question which is worth to answer.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 07:52:34 pm
content: Quote from: ogden on October 05, 2019, 07:20:50 pmLOL sorry if I sounded like I did ask for a silver plate and you build it to:-)What I men was a drawing ehm... is it called a block diagram? On how you would mount it, I presume a simple voltage divider with two resistors? 1:2 / 1:10 or? But before the offset trimming? and then the probe diagram?

author: ogden
author_rank: Super Contributor
timestamp: October 05, 2019, 08:05:38 pm
content: Quote from: FriedMule on October 05, 2019, 07:52:34 pmYes, I got it. You want diagram? Then draw it.QuoteWho knows. You want me to give exact divider ratio? This is what I call providing something on silver plate. First you need to know input voltage range of the existing design, gain and output range as well. After that you will start to get clue about voltage divider. BTW simple, two resistor divider won't work on 500MHz probe. It (divider) shall be frequency-compensated.BTW you expect me to answer your questions, yet you ignored to answer mine - about your scope and it's bandwidth.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 08:33:30 pm
content: Quote from: ogden on October 05, 2019, 08:05:38 pmSorry trust me I am not asking for any silver platter, every time it sounds like that, please blame my missing language skills! There is no fun in electronic if you either buy it finished or make someone do it for you, but also no fun in getting lost way over your head:-)Sorry forgot about your scope question: it's a 2-Channel 500MHz LeCroy LT342L

author: ogden
author_rank: Super Contributor
timestamp: October 05, 2019, 09:27:30 pm
content: Quote from: FriedMule on October 05, 2019, 08:33:30 pmGood. Now we at least know that you possibly/actually may need what you ask for. Sorry for my seemingly non-forthcoming attitude as well - we are tired of those who come and expect somebody else do their homework. When you show that you are seeking answers yourself and need just guidance or even better - confirmation that you are on right track, you will get increasingly better feedback from others.For example you just blindly guessed two values of divider out of thin air w/o showing that you invested your time finding it (divider ratio). Do you think that seeing that I want to invest my time in return to solve problem which is not actually mine? Hint: not at all.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 09:43:06 pm
content: Quote from: ogden on October 05, 2019, 09:27:30 pmYou are completely correct, I have, on an other subject and forum, med many who did expect everything on a silver... hmm no say gold platter and was annoyed that no one did jump at the chance. So I do understand your reaction. :-)My 1:2 / 1:10 was as to ask about if you did mean something like a 1:2 or 1:10, not thinking of some certain number but only if you meant a:b resistor thingy.I know that it would be stupid of me to start recherching the wrong place, so I'd rather ask again and maybe sound stupid, then waste your or my time:-)EDIT: By the way, I do really appreciate that you tell me how my bad English is being read! It helps me so much and I have to try to be better to formulate what I want to say, so that my text really do express what I mean. So many many thanks!! :-)

author: ogden
author_rank: Super Contributor
timestamp: October 05, 2019, 10:20:31 pm
content: Quote from: FriedMule on October 05, 2019, 09:43:06 pmYes. Two resistors. Like common 1:10 scope probe. Thou to reach 65 volts with that design, most likely other ratio needed. That's your homework to investigate and try to think of ratio and actual value of those.QuoteI think you are doing fine.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 05, 2019, 11:13:31 pm
content: Quote from: ogden on October 05, 2019, 10:20:31 pmYes now comes the fun part, first do I have to find out the max voltage the probe can handle safely, then the devider, I hope:-)Thank you so much for helping me in so many ways!EDIT: oh forgot, and this may I need on a silver platter:-)I know that the author has only tried the B variant, but the variants are way over my head, is it possible for me, in any way, to decide what variant is best for my usage or can you see any obvious candidate?

author: ogden
author_rank: Super Contributor
timestamp: October 06, 2019, 05:37:27 am
content: One author actually finished, B

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 06, 2019, 12:27:16 pm
content: Option B is just a standard instrumentation amplifier (IA) circuit made out of 3 individual op-amps. You can buy an IA as a single IC but it won't have a very high gain*bandwidth product - maybe 10MHz at unity gain. Using individual high speed (and looks like current-feedback here) op-amps makes it easier - though not easy - to achieve an arbitrarily high bandwidth.Note that the voltage divider at each input of a high bandwidth differential probe needs to be precise both at DC, which is easy - just choose the correct resistor values - and across the entire frequency range, which is deceptively difficult to pull off, especially if you need >2:1 attenuation and >10MHz bandwidth.You want something like 500MHz bandwidth which implies the probe having a -3dB bandwidth that is at least Pi times higher (and ideally closer to 10x). This is just enormously difficult to do and commercially available active differential probes with >2GHz bandwidth have 5 digit prices, and I don't mean in Yen or Yuan. You need to set your sights much lower or else buy a probe outright, or, perhaps, copy a successful design *exactly*.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 01:05:34 pm
content: Quote from: MagicSmoker on October 06, 2019, 12:27:16 pmOkay yes it makes a bit harder, I have tried to find sub 1GHz probe designs and I have also found some, but I do not know how good they are. If you look at the design I have chosen here, it should work fine up to about 800MHz but only in super low voltage. The design you can buy are for the most for high voltage and yes costs 4 times my scope.I have read every comment in this tread:https://www.eevblog.com/forum/testgear/gt-1-ghz-diy-differential-probes/Found other probes like this:https://xellers.wordpress.com/electronics/1ghz-active-differential-probe/But my "wall" is simply that I do not have enough knowledge to build my own, so I have to, as you say, copy a design.But untill now, I have not found a design that your great guy's says do work.

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 06, 2019, 01:51:25 pm
content: Quote from: FriedMule on October 06, 2019, 01:05:34 pmI (and ogden) have already told you this is an enormously difficult task, and your only hope - hell, my only hope! - would be to copy someone else's design exactly. I mean, the same components, board layout, physical construction, every last detail.This is not the sort of problem a beginner is likely to run into, nor even the sort of problem any but RF and high-speed digital design engineers will ever have to contend with, frankly, so I have to ask why you think you need a >500MHz differential probe? Earlier you wrote this:Quote from: FriedMule on October 05, 2019, 10:39:28 amBut that isn't an answer. Suffice it to say that there are precious few instances where an RF or high speed digital signal is not supplied by an isolated power supply, so there isn't a safety requirement for needing a differential or isolated probe. There are plenty of examples of high speed differential digital signal standards such as Ethernet, LVDS, HDMI, SCSI, etc., but, again, not the sort of thing the typical EE will ever work on at the signal level, much less a beginner or hobbyist.So what, exactly, do you intend to probe with an oscilloscope that has convinced you you need a really expensive differential probe good for (much greater than) 500MHz?

author: BravoV
author_rank: Super Contributor
timestamp: October 06, 2019, 02:00:52 pm
content: A 500MHz differential probe capable of < 65Volt ... cheap ... DIY & relatively easy to build ... just nope.Suggesting to change plan.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 03:29:50 pm
content: You are all a great bunch of guys!! :-)Okay I did not know that my project was so outrageous, if it is a futile goal for me right now, then let be refrace my question then. What would be a doable probe attachment that can handle up to 65V with isolated ground and ???MHz?Functioning but not necessary looking like this:Could I use either:http://blog.weinigel.se/2016/02/26/ghz-differential-probe.htmlOr:https://xellers.wordpress.com/electronics/1ghz-active-differential-probe/As template, they both have circuit design and component list.

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 06, 2019, 03:41:39 pm
content: Quote from: FriedMule on October 06, 2019, 03:29:50 pmYou want us to spend considerable time assessing projects for you but still haven't answered the most basic question which has been asked several times already: What Are You Trying To Measure?

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 03:53:11 pm
content: Quote from: MagicSmoker on October 06, 2019, 03:41:39 pmSorry if I have not explained that in a good enough manner, I did try at my comment number 6:https://www.eevblog.com/forum/beginners/diy-differential-probe-again-again-please-help-)/msg2725412/#msg2725412But please ask any question I may not have answered.

author: Marco
author_rank: Super Contributor
timestamp: October 06, 2019, 04:57:34 pm
content: Coax is inherently asymmetric, that makes a differential measurement pretty much impossible at high frequencies with a single oscilloscope probe. A 500 MHz amplifier which can directly take +/- 65 V on the inputs without dividers is implausible too, so you need dividers.So you need either a small probe with 2 pins directly going to dividers and then a differential amplifier. Or two divider probes going to a differential amplifier. For the divider probes you can have oscilloscope probes, or coax divider probes.The only existing design which somewhat meets your requirements isSmith's balanced coax probeusinga power combiner. But it can't work down to DC, in fact you probably need to add blocking capacitors so the common mode doesn't blow the combiner. You could hybridize this, by adding two extra wires and using a normal low frequency differential probe (ie. high impedance dividers with an instrumentation amplifier) for the low frequencies and Smith's probe for the high frequencies.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 05:23:37 pm
content: Quote from: Marco on October 06, 2019, 04:57:34 pmOkay, thanks for the link, I hav not read it all yet but can see that it do not contain any diagram, so it may be great to read but maybe also hard for me to copy from, like the other say I have to, to get a little chance for something useful. :-)hmm... What if I use my standard 10:1 probe infront of the probe circuit? That will give about 6.5V and then make a divider that I have to calculate (I know that it may not be easy) and maybe end up with a 10-100MHz. I shall not pretend that I know what a coaxial divider is, but that is only fun to find out:-)

author: ogden
author_rank: Super Contributor
timestamp: October 06, 2019, 05:32:49 pm
content: Quote from: FriedMule on October 06, 2019, 03:53:11 pmTHAT project do not need differential probe. It does not even need scope. Thou may benefit from proper signal gen, not necessarily 500MHz. There is nothing wrong about being beginner, but before drawing moon rocket plans, you shall *build* at least one working paper plane first. So I strongly suggest you to carefully consider following advice:Quote from: MagicSmoker on October 06, 2019, 12:27:16 pm

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 05:48:43 pm
content: Quote from: ogden on October 06, 2019, 05:32:49 pmYou are completely correct that it may not need a probe but, as a beginner, I would like to see where what is happening, on top of that do I plan on building a simple PSU for it, just to learn what PSU "signal" do to that circuit, what make the 500MHz behave wrong, bad or you know. :-) So selected a project that is easy-ish to make, had max MHz my scope can handle to learn what happens and how do my scope react... Or in short, just to see what is going on all sort of places in the circuit.LOL I love the way you say it about not building a space rocket before even learn to fold a paper plane:-) But again as a beginner, it is hard to know what is a paper plane project and what is a moon landing:-)

author: ogden
author_rank: Super Contributor
timestamp: October 06, 2019, 06:08:37 pm
content: Quote from: FriedMule on October 06, 2019, 05:48:43 pmWell.. Everything is fine while you do not require your 65V common mode range for high speed differential probe. That is very "unusual spec" if I can say so. Either stick with common mode range of existing DIY diff probe designs or do not call it "easy-ish to make". Please do not get me wrong - I am not trying to discourage you from your idea. Sometimes brave ideas of unaware are surprisingly successfulYet I stillafreeagree that you better start with building *exact* copy of working diff probe, then think of increasing it'scommon modevoltage range.Why do you think 1:10 500MHz scope probes cost so much? - because of probe manufacturer's cartel?

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 07:05:14 pm
content: Quote from: ogden on October 06, 2019, 06:08:37 pmThanks:-) The 65V is due to it's max I do work with and why not build it to be able to handle max. (my innocent thought) By easy-ish I meant the project board at 500MHz, not the probe:-) I did / do think that most electronic, made by Agilent and other is much more expencive then needed to be, due to name, manufacturing and the 1000V capabilities. So I did thought, DIY and low voltage (65V) would be much cheaper and maybe not as difficult as a 2GHz 1000V Agilent you can buy.I have two channels and would like to measure on maybe the PSU while also look at the 500MHz board, so that's why.

author: ogden
author_rank: Super Contributor
timestamp: October 06, 2019, 07:23:18 pm
content: Quote from: FriedMule on October 06, 2019, 07:05:14 pmUrban myth. If you have ANY 500MHz "original/brand" probe, then buy cheap 500MHz probe from China (if any) and compare. You will see that "you get what you pay for" saying makes sense.QuoteDreamer65V differential probe that compares to 2GHz 100V Agilent probe may take years of your "career" and all your savings. Better just buy one. Failure to complete my 10 minute homework even after so many posts just confirms that probe you are dreaming about is above your paygrade. Sorry.

author: rstofer
author_rank: Super Contributor
timestamp: October 06, 2019, 07:27:36 pm
content: Quote from: FriedMule on October 06, 2019, 07:05:14 pmDon't forget the cast of dozens that worked on the design, the management that lead the project and up the chain. Then there is the cost of safety certifications and the ever important QA department. Those are substantial costs to be recovered from what is bound to be a low volume device.It's easy to build a Rigol DS1054Z and sell it for $400 when they are going to sell millions of units. I doubt that Keysight has many customers for their $300,000 model. I rather expect it is built to order.The EEVblog store has Dave's differential probe for sale for A$350 but the bandwidth is just 70 MHz. It has a voltage range switch for dealing with up to 700V differential.https://www.eevblog.com/product/hvp70/Sapphire makes Dave's probe and many others that get rebadged by the scope manufacturers. Look at the list here and see if what you need is even manufactured. For the higher voltages, 100 MHz looks like the limit.https://www.nbn.cz/Sapphire/Sapphire%20Instruments%20CO_%20LTD%20produts_files/pproducts.htm

author: rstofer
author_rank: Super Contributor
timestamp: October 06, 2019, 07:40:07 pm
content: Quote from: FriedMule on October 06, 2019, 05:48:43 pmNot really! Just create a spreadsheet of specs and price. Specs would include Common Mode (AC+DC) Max Voltage, Differential Max Voltage, Switchable Voltage Ranges, Bandwidth and so on. Maybe one column for each.You might include a column for Safety Certifications and another for Warranty.For voltages less than 50V (peak to ground), I might not get too concerned about safety certs but beyond that, where voltages become life threatening, I would have a lot more concern. That's why I keep my projects at of below +-15V.

author: MagicSmoker
author_rank: Super Contributor
timestamp: October 06, 2019, 08:01:48 pm
content: You don't need a differential probe unless you are either looking at differential signals (I gave examples earlier) or a signal which is elevated from ground, such as the gate drive to the upper switches in a bridge converter (that likely didn't make any sense, but f it, it's a good example).Neither condition applies for that battery power RF thingamajig, nor does the need for >500MHz of bandwidth.I find it amusing when a beginner/clueless noob can't see why something costs so much to make. Well, here's a clue when it comes to >500MHz active/differential probes: the stray capacitance of two 1cm teflon-insulated wires twisted together (called a "gimmick", btw) is about 4pF, and that meager amount of capacitance has a reactance (AC equivalent to resistance) of 80 Ohms at 500MHz. Heck, the stray capacitance of a typical chip resistor might be in the half-a-puff range, so equivalent to about 640 Ohms. THAT is why differential probes are so difficult to design once either/both a high voltage division ratio and/or high bandwidth are required.EDIT - forgot to put the frequency in for the reactance examples.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 08:45:41 pm
content: Quote from: ogden on October 06, 2019, 07:23:18 pmIt makes a lot of sense, my thought just comes from so many other things you can buy that alone is expensive due to brand.I think that most probes are above my paygrade, even the "cheap" one:-)Quote from: rstofer on October 06, 2019, 07:40:07 pmWhat a fantastic idea, thanks, it "forces" me also to dig deeper in what I am about to jump into, so that is a thing I will do from today and on! :-)Yes above 50V is some nasty stuff and can even be dangerous already from 40V or even lower if all things goes wrong!Quote from: rstofer on October 06, 2019, 07:27:36 pmYes I have looked at these also but the price did frighten me and then did I think: "why not make it myself, it is a few components and I do not require GHz+ or high voltage, so even cheaper" LOL was I wrong:-)My reason for talking about differential probe, is that, that's what I did find out after several weeks of searching, but is it what I need?I "just" want to be able to measure two places where the ground is not the same or where I am not sure if a common ground connection will give me a wrong result.EDIT: Sorry for this maybe infantile addition but I imagine some circuit where it measures the difference between ground and probe point, send that voltage out to the scope, so lets say DC difference of 15V gives the scope a 10:1 or 1.5V or AC 2VP to P sends 0.2V to the scope.

author: The Senate
author_rank: Newbie
timestamp: October 06, 2019, 09:45:07 pm
content: I found the Elektor article for the probehttps://archive.org/stream/ElektorMagazine/Elektornonlinear.ir2014-09#page/n45/mode/2up

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 06, 2019, 11:45:47 pm
content: Quote from: The Senate on October 06, 2019, 09:45:07 pmThank you wary much, I'll read it now!:-)

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 08, 2019, 05:11:55 am
content: in the above article abut an isolated circuit there is talk about two isolated chips, the one has Isolated Power, the other not, what is that? I have looked at Wikipedia, and other places but I only find articles about sport and other like that, the wii page do not talk about Isolated Power while it do talk about digital isolator's.

author: ogden
author_rank: Super Contributor
timestamp: October 08, 2019, 06:07:57 am
content: Quote from: FriedMule on October 08, 2019, 05:11:55 amYou shall try internet search instead of wikipedia.https://lmgtfy.com/?q=AMC1200. findchips.com is another good place tofind chips. In short: It is±250 mV-Input Basic Isolated Amplifier for Current Sensing. Kind reminder - that isolated probe has <= 60Khz bandwidth and it is not differential. BTW Elektor article explains everything in details, includingthat chip(attach)

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 08, 2019, 07:41:07 am
content: Quote from: ogden on October 08, 2019, 06:07:57 amI have tried google and there are a lot of links, but not any explanation on what Isolated Power means in a digital isolator.Yes I saw that about the 60KHz and it is only an isolated probe but I am not sure what I need, isolated or differential.My goal is to be able to measure two different places at once, i.e before the bridge rectifier and before a chip much later in the circuit.Or short, no common ground between the two measurements.

author: BravoV
author_rank: Super Contributor
timestamp: October 08, 2019, 07:55:41 am
content: Quote from: FriedMule on October 08, 2019, 07:41:07 amImo, what you want there is not cheap or easy, let alone DIY project for beginner.Usually, when the times there is need to measure this kind of measurement points, the best is to use a fully isolated oscilloscope, mostly handheld and not cheap.No, ordinary scope can't do it, and even using HV differential scope, you need two of them.Once you own it, you can freely poke and clip the probe's ground clip at anywhere you like as below example.

author: ogden
author_rank: Super Contributor
timestamp: October 08, 2019, 08:01:22 am
content: Quote from: FriedMule on October 08, 2019, 07:41:07 amThat digital isolator IC have isolated dc-dc power converter inside. Did I answer your question? You may ask further questions.Quote from: FriedMule on October 08, 2019, 07:41:07 amFor that you do not need differential probe, nor 500MHz bandwidth. As you ask surprisingly simple questions, I am afraid that instead of building something safety-related, you shall consider buying one or two HV diff probes:https://www.eevblog.com/product/hvp70/. Alt least then there will be less chances of you killing yourself.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 08, 2019, 08:18:28 am
content: Quote from: ogden on October 08, 2019, 08:01:22 amThanks for your concern! the "funny" thing is that I know way more about main power and have done several installations, while I know nearly nothing below 220V.I am not concerned about my safety, since I will take safety precautions that can be considered total over"kill":-)I have seen what power can do when it want to and that's scary!! 400V 1000A can do things a hand grenade only can dream of!But on the other side, will I keep it below 50V, my example was bad but just to illustrate that I want to neasure one place with the normal probe and then the other with the isolated probe. One of the hard ting to do I to search or explain what I want when I don't know the therms, words and possibility, on top of that is my English wary bad and do not make it easier.When I have found out what i need, isolated or diff, then begins my search again for articles, diagrams and gerber files. :-)