Curve tracer designs? - Page 1
Forum section: electronics / projects

author: 0culus
author_rank: Super Contributor
timestamp: November 18, 2018, 02:01:24 am
content: So I've been thinking that it would be handy to have a curve tracer in my lab, but even more, it would be fun to make it myself. I've looked at a variety of designs, some requiring mains voltage, some not. I tried soldering this one up on a protoboard today because I have all the parts on hand and no transformer required (except I omitted the switch for a prototype):http://www.electronics-lab.com/diy-generic-curve-tracer/But, it seems to not be working at all, mainly the 3904 never starts oscillating so there's no signal being put through the DUT.Are there better designs for a curve tracer that are similarly parts-efficient? Thanks!

author: JoeO
author_rank: Frequent Contributor
timestamp: November 18, 2018, 03:00:56 am
content: The schematic shows a 3M resistor while the parts list calls out a 2M resistor.Have you tried them both?

author: 0culus
author_rank: Super Contributor
timestamp: November 18, 2018, 05:04:07 am
content: Quote from: JoeO on November 18, 2018, 03:00:56 amYeah, I tried 3Mohm too and it still doesn't work. There's 0.584 V on the base of the transistor and 6.160 V on the collector in that arrangement, and there is nothing at the emitter. Fairly sure the transistor isn't backwards.

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2018, 09:24:20 am
content: Try another 2N3904, and what capacitor are you using for C1, C2 and C3, they need to be 63V or higher mylar foil types, as ceramic or electrolytic capacitors leak way too much. Bias is turning the transistor on, but either there is leakage or a bad connection.

author: 0culus
author_rank: Super Contributor
timestamp: November 18, 2018, 08:38:25 pm
content: Quote from: SeanB on November 18, 2018, 09:24:20 amOK. I only have a few of those kind of caps unfortunately, and not in the right spec. Guess it's time to order some. The 4.7nF ceramics I have don't seem to be leaking DC, but the 1uF electrolytic I used is definitely leaking.

author: 0culus
author_rank: Super Contributor
timestamp: November 18, 2018, 09:47:05 pm
content: So there's an 890 Hz mostly clean oscillation happening on the collector of the 3904. I think I'm going to order some better quality caps and some other parts and build another prototype on breadboard.

author: m3vuv
author_rank: Super Contributor
timestamp: November 19, 2018, 12:24:27 am
content: i built the same jobby a while ago,never did get it working properly!

author: 0culus
author_rank: Super Contributor
timestamp: November 19, 2018, 12:55:22 am
content: Hmm, maybe it's time to find a better circuit then.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 19, 2018, 02:56:17 am
content: Hi,have you seen the curve tracers of ChangPuak from the ETH in Zurich, Switzerland ?https://www.changpuak.ch/electronics/Curve_Tracer_advanced.php

author: johnwa
author_rank: Frequent Contributor
timestamp: November 21, 2018, 10:23:32 am
content: Hi,Here is an overview of a curve tracer I built recently, don't know if this is of any help:It all started when I was wondering what to do with this old oscilloscope that a friend gave me some years ago. I already had an analogue scope, and I was thinking of giving this one away to some deserving newbie, but it was in pretty poor shape: noisy switches, timebase not working, and I had already needed to make a repair to the EHT supply using the tripler out of an old TV set. So I decided, rather than burden someone else with it, I would convert it into a dedicated curve tracer.To provide the drive signal, I used an amplifier out of some old PA equipment. This circuit used a couple of quasi-complementary 2N3055s, and was good for about 40W into 8 ohms. Conveniently, I managed to find some suitable +/- 35V supply rails inside the scope to power it. Maximum output swing is about +/-33V.For the oscillator, I got lazy, and ordered a sine/square/triangle signal generator module from ebay, for the grand sum of $3.50. This feeds a front panel attenuator (I repurposed some of the controls in the timebase module), and some switchable level shifting to provide positive, negative, or AC output. I also added an adjustable current limiting circuit to the amplifier. (Let me know if you would like details).The output of the amplifier is connected to the CH1/X input, which then becomes the drive output. The CH2 input has a 1 ohm resistor connected across it, to act as a current shunt. The input attenuators work as normal, with the CH2 one being recalibrated in amps instead of volts.I also added a base drive staircase generator, based on the Elektor December 1989 circuit. (I think someone may have posted this on the forum somewhere - search around)In the picture, the original X deflection board is at the back, then comes the amplifier module. The function generator is at the top, with the staircase generator below it. The current limiter is partially hidden behind the heatsink.Edit 21/11/2018: spelling

author: Wolfgang
author_rank: Super Contributor
timestamp: November 21, 2018, 12:59:33 pm
content: Love it. POOGE at its best !

author: rhb
author_rank: Super Contributor
timestamp: November 23, 2018, 03:27:13 pm
content: I wanted to build one of these many years ago, but never got around to it.In 2018 I have to ask a simple question.Why would you not use a fast ARM MCU with stereo ADC/DAC feeding suitable op amps? One channel for the base drive and one for the collector with the ADC taking readings.I have a Peak Technologies DCA75 which does a decent job, but it only reports Vbe_sat and Vce_sat. It will do curve tracing with the PC software. My BSIDE ESR02 Pro reports Vbe_turn_on, but not Vbe_sat, etc.I've not done any in depth analysis of what a good transistor tester should do, but it seems to me that there is room for considerable improvement at low cost.

author: 0culus
author_rank: Super Contributor
timestamp: November 24, 2018, 04:08:06 am
content: Quote from: johnwa on November 21, 2018, 10:23:32 amOh that's really neat! Thanks for sharing. That would be a totally awesome use for an old scope in the future.Quote from: rhb on November 23, 2018, 03:27:13 pmWhile that would likely work, I personally prefer analog test equipment.My main scope is a Tek 2465B.

author: rhb
author_rank: Super Contributor
timestamp: November 24, 2018, 05:13:03 pm
content: Certainly a valid reason. I bought a refurbished Tek 485 from Reed Dickinson via eBay precisely to have an analog scope to double check strange stuff from DSOs.

author: 0culus
author_rank: Super Contributor
timestamp: November 24, 2018, 09:12:49 pm
content: I will probably try to get a decent digital scope at some point to have access to the nice features they have, but I certainly wouldn't want it to be my only scope!On another note, I tried building another prototype of this circuit with some better caps and I am pretty sure the design originally mentioned in the OP doesn't work.

author: rhb
author_rank: Super Contributor
timestamp: November 25, 2018, 12:33:52 am
content: No worries, mate.https://www.tinaja.com/ebooks/TTLCB1.pdfpage 219

author: glue_ru
author_rank: Contributor
timestamp: November 25, 2018, 02:03:16 am
content: Quote from: 0culus on November 18, 2018, 05:04:07 amwould it help to add a schottky diode to get better switching

author: rhb
author_rank: Super Contributor
timestamp: November 25, 2018, 02:30:05 am
content: Quote from: 0culus on November 18, 2018, 05:04:07 amThe voltage drop across the BC is lower than across the BE junction. Forty years ago I built a bunch of very simple things using 2N2222s from Radio Shack, but none of them worked. I went around asking everyone I knew how to identify the C & E leads. No one knew.As a break from looking through a microscope all day for my MS I attended an Electronics 101 class in the next building taught by a solid state physicist who had built a computer out of TTL logic just before the 8080, 6502 and such appeared.One day he said, "The forward resistance across the base collector junction is lower than the forward resistance across the base emitter junction because the greater area of the collector exceeds the effect of the greater doping of the emitter." All I had was an analog VOM, but sure enough, he was right and the reason nothing worked was the pinouts on the back of the package were wrong!With modern DMMs you need to use the diode test function as the resistance ranges don't put out enough voltage to forward bias the junctions.

author: 0culus
author_rank: Super Contributor
timestamp: November 25, 2018, 03:26:06 am
content: Quote from: rhb on November 25, 2018, 12:33:52 amWow, that is very cool. Thanks! Saving that!Quote from: rhb on November 25, 2018, 02:30:05 amMy Fluke 87V seems to have no trouble driving it in resistance mode; it would appear that I don't have the 2N3904 backwards by that heuristic. The base-collector is ~475k and the base-emitter is ~486k. In diode test mode, the base-collector is 0.707 V and the base-emitter is 0.712 V.

author: rhb
author_rank: Super Contributor
timestamp: November 25, 2018, 04:02:54 am
content: Don wrote wonderful books. There's an entire generation that acquired much of their knowledge of electronics from Don and a handful of other writers. If you can explain it to a teenager, you *really* do know what you're talking about.It took about a minute for me to find the circuit even though it is not indexed as a "staircase generator". I knew it was in there, so I just had to think of synonyms. I have been surprised at how often that's the book I grab off the shelf. I read it so much I know what's there and I'm just checking that my memory is correct.If you want to really be old school you can build it all from discretes. Might have to.BTW the "which is C and which is E" was my favorite question when I ran across someone who was *really* good at electronics. No one was able to answer it until I ran across someone online a few years ago. Fundamentally the difference between a scientist and an engineer. Scientists rely on first principle and engineers on rote. I feel pretty sure everyone I asked enjoyed the answer. I *only* asked people who were "walks on water" good. People like that enjoy such little subtleties. It is the pleasure derived from such things which made them good.

author: 0culus
author_rank: Super Contributor
timestamp: November 25, 2018, 06:13:43 am
content: Which circuit are you talking about?This is a book I might have to find a hard copy of.That is a neat little subtlety, thanks for sharing!

author: rhb
author_rank: Super Contributor
timestamp: November 25, 2018, 01:15:19 pm
content: Quote from: 0culus on November 25, 2018, 06:13:43 amThere are only two circuits in this discussion that I know of. The one you've been trying to get to work and the one on page 219. If you're asking about the reference to discretes, that was the counter chips.This is what is commonly referred to as an R2R ladder DAC. A relevant concept from the same book is using a counter to index a memory and using the output of the memory to feed the R2R. That will let you correct for resistor tolerances by just modifying the contents of the memory. The JDS 6600 arbitrary waveform generator uses an R2R ladder driven by an FPGA.QuoteAs it happens I have a spare I got when someone was cleaning out there office. How about $4 plus media mail?QuoteDon's books are full of neat little circuits. I'd bet you would find a lot of them in Tek and HP gear of the era. The Tek 577 probably uses the circuit Don showed.

author: 0culus
author_rank: Super Contributor
timestamp: November 26, 2018, 04:04:23 am
content: Quote from: rhb on November 25, 2018, 01:15:19 pmTurns out amazon has a number of books by him.

author: rhb
author_rank: Super Contributor
timestamp: November 26, 2018, 02:22:24 pm
content: I asked Don. His best guess is that with foreign press runs the TTL CB sold about 1.4 million copies. That means that pretty much anyone with a strong interest in electronics in the 70's bought a copy.Pretty heady stuff for a 30 something tech writer. It went through 3 printings in the first year!The other books which are still very relevant are the CMOS CB and the Active Filter CB. The RTL CB might be useful if you need to build basic logic. Unfortunately, lots of the 7400 series devices are no longer available except at steep prices.The schematics and service manuals for the gold standard, the Tek 577, are available. I suggest studying those. The Tek service manuals of that era include a detailed explanation of the theory of operation of *every* circuit in the instrument.

author: 0culus
author_rank: Super Contributor
timestamp: November 26, 2018, 05:11:46 pm
content: Quote from: rhb on November 26, 2018, 02:22:24 pmVery cool. I've got the ones Amazon still has in my cart. I will grab those manuals too. I've always wanted a 577 but sadly I haven't the space in my current lab!

author: bd139
author_rank: Super Contributor
timestamp: November 26, 2018, 05:52:11 pm
content: Another one. Heathkit IT-3121:https://www.rsp-italy.it/Electronics/Kits/_contents/Heathkit/Kits/Heathkit%20IT-3121%20semicond%20curve%20tracer%20schem.pdfFor low voltage stuff I have a 33120A which has a floating outputSimples - one resistor + 33120A + two probes:Tunnel diode (both channels inverted here because I was half asleep):1N4148:

author: 0culus
author_rank: Super Contributor
timestamp: December 04, 2018, 05:54:39 am
content: Got some books today, rhb.

author: bd139
author_rank: Super Contributor
timestamp: December 04, 2018, 07:50:26 am
content: Excellent books. Have both as well

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 04, 2018, 09:00:41 pm
content: I'm pretty sure this is the same circuit National Semi published many years ago. It only does a single curve, but might be useful for some ideas-https://www.onsemi.com/pub/Collateral/AN-6610.pdf.pdf

author: 0culus
author_rank: Super Contributor
timestamp: December 04, 2018, 10:56:42 pm
content: Quote from: bd139 on December 04, 2018, 07:50:26 amWas thinking of picking up his filter cookbook as well! Really enjoying his accessible writing style.Quote from: Conrad Hoffman on December 04, 2018, 09:00:41 pmThanks!

author: rhb
author_rank: Super Contributor
timestamp: December 05, 2018, 02:35:15 am
content: Now you have some inkling of why when the "Was Don Lancaster Really A Guru" thread appeared I was ROFL.His Active Filter CB, TTL CB and CMOS CB were his major works. But with the (according to Dave) 32 others he wrote, I'd say its a safe bet he sold close to 10 million books in total. Quite possibly more. If that is is not superstar status for a tech writer, I don't know what is.Realistically only 3-5% of the population has the interest and motivation for STEM. And as a society, that's all we need. The same thing applies to the skilled trades and other professions. In the 70's and 80's if you did not have several Don Lancaster books you simply were not STEM material.You have really got to know the subject to write that well on complex topics.BTW What printing are your copies? I have a very worn 2nd printing of the TTL CB which I bought and a near new 3rd printing which I scavenged at work. Both of mine are the original green cover.

author: 0culus
author_rank: Super Contributor
timestamp: December 05, 2018, 06:48:01 am
content: Quote from: rhb on December 05, 2018, 02:35:15 amI'm not entirely sure...the TTL cookbook has a blurb in the cover about how to read the printing code, but I can't find the code! The CMOS book says "transferred to digital printing in 2010".

author: JoeO
author_rank: Frequent Contributor
timestamp: December 05, 2018, 12:44:02 pm
content: Quote from: 0culus on December 05, 2018, 06:48:01 amYou make no sense. "in the cover" you wrote? Where exactly is that?What version TTL book are you referring to?You are either a troll or someone with a room temperature IQ.

author: 0culus
author_rank: Super Contributor
timestamp: December 05, 2018, 06:44:02 pm
content: Quote from: JoeO on December 05, 2018, 12:44:02 pmLove you too, mate. <3 It takes one to know one, as they say.

author: rhb
author_rank: Super Contributor
timestamp: December 06, 2018, 03:25:08 am
content: @JoeO Perhaps you should make sure you understand what people are talking about before commenting. And introducing yourself by insulting people won't get you very far around here. At best you will be ignored. And people do get banned for bad behavior. This is Dave's establishment. You should read the rules.My copy of the CMOS CookBook is a 5th printing from 1980. The book was copyrighted in 1977. So based on the 2010 date at a minimum it was still being sold 33 years later. That's really quite astonishing for a book on device level electronics technology. And a very strong testimony to the quality of Don's writing.BTW typical printing code now is a list of integers from 1 to N and the first integer in the list is the printing. It appears on the copyright page.

author: 0culus
author_rank: Super Contributor
timestamp: December 06, 2018, 04:16:12 am
content: Quote from: rhb on December 06, 2018, 03:25:08 amHere's the copyright page on mine, attached below. Is it part of the ISBN? I'm confused about the little explanation because I can't find any numbers that match what it describes.

author: Simon
author_rank: Unknown
timestamp: December 06, 2018, 07:30:43 am
content: Quote from: JoeO on December 05, 2018, 12:44:02 pmCalm down!

author: bd139
author_rank: Super Contributor
timestamp: December 06, 2018, 08:16:22 am
content: I don’t think that lame insult is as bad in the US as it is here

author: Simon
author_rank: Unknown
timestamp: December 06, 2018, 08:19:26 am
content: Yea well nuf said, if in the US they want hot houses and silly temperature measuring systems that is up to them, the rest of the world reads that differently.

author: rhb
author_rank: Super Contributor
timestamp: December 06, 2018, 06:19:47 pm
content: Quote from: 0culus on December 06, 2018, 04:16:12 amI think it's the switch to "book on demand" printing which was something Don championed. So there no longer are printings in the traditional sense for low volume books. But there's actually a 2nd edition in 1997, but it's pricey. I'd guess it's being used in college and votech courses. You still have to learn digital logic even though you're more likely to use an FPGA. The fact that the 2nd ed has a 2nd author is a clear sign that Don just didn't want to keep writing books. So when Sams asked for a revised edition, Don told them to hire another writer.The thing that is *really* amazing is that Don's major classics are still in print after over 40 years! I cannot think of any electronics book that has been in print that long. Wow!!!!That's not a guru, that's a Bodhisattva!!!

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 06, 2018, 07:12:09 pm
content: Quote from: rhb on December 05, 2018, 02:35:15 amI guess I had seen those books around in that time period, but never picked one up. Since my focus was IC design, they did not support the path I was on.They are still available...maybe I should pick one up. Like...I need more books...lol

author: icpart
author_rank: Regular Contributor
timestamp: January 22, 2019, 08:45:28 am
content: Hi guys. I think I found the BEST ever DIY curve tracer so far. Very interesting project with full source of PC program and MCU firmware. Also I think the software have the function to be used also as Impendance analyzer which is great. Recently for that I bougth Analog Discovery Impendance meter board and so far is also great. Only downside of that project is the author use old MCU which is expensive and USB-serial board which are the most expensive parts in that project.Project page:http://www.kc4zvw.us/project5.htmlDescriprion of project:http://www.arrl.org/files/file/QST%20Binaries/Apr2015/Expanded%20Text.pdfSource code and PC software:http://www.arrl.org/files/file/QST%20Binaries/Apr2015/Source-Codes-and-More.zip

author: 0culus
author_rank: Super Contributor
timestamp: January 29, 2019, 12:21:29 am
content: That site is unreachable for me.