Let's Build this Curve Tracer!

Noise and thermal drift cause aplitude instability, due to that wien bridge oscillators need some sort of stabilizing circuitry, to whit a bulb.

Jeff Chaney

Hi Paul, can I use a -12, 12 V power supply for this project?

Francisco Velazquez

Another variant of the Octopus device tester

nosaj seveer

Interesting implementation! I always thought that curve tracers used a ramp type signal for the current (or voltage) that is supplied to the DUT.

Andre

Does the frequency signal in have to be a sine wave or can it be a square wave ??

Brian007a

I am so pumped, got my curve tracer working tonight! I put it away for a month because I couldn't figure it out, and I had two problems: One was I had a cap in backwards. That was overloading my power supply. Once I fixed that, I couldn't quite get it working. I had substituted a 7381 bulb for a 7380. Both are 6.3V, but different amp. I guess I don't really understand what the bulb is doing in the first place. I took a screen shot, and I'm also very pleasantly surprised at the XY capabilities of my siglent 1104 box: https://www.dropbox.com/s/z054tritnun4w2n/curvetracer.png?dl=0

Golf League Tracker

Great work

LoSaYa

Is it possible to use a Tektronix 224 for this curb/signature tracer ? can I integrate inside to scope ? somebody did 'it ?

Eric Groslevin

I've only just started watching the Patreon videos, even though I have been a Patreon member for some time. This circuit is genius. The total embodyment of how simplicity can win out over anything more complex. Fantastic!

Brendan White

Hi David, would you not call the point where the two batteries are joined the "physical/actual ground" connection, rather than "theoretical ground" as it is absolutely critical that it exists in the circuit for functionality, and that +/- supply ground(s) point would be tied to the probe input ground, osc input ground, and H/V signal output grounds as well as the ground at the bottom of the VR on the schematic

Don Stewart

Kuba's explaination above is a good one, to wrap you head around the concept of a dual rail +ve15 volt and -ve15 volt, try using a couple of PP3 9 volt batteries as an example, when you connect the positive terminal of one of the batteries to the -ve of the other battery you are connecting them in series to give you a theoretical single battery that gives you 18 Volts, if you measure the voltage with a multi-meter from the +ve and -ve terminals that are joined together to the terminals of the two batteries that are not joined together you will get +9V on one and -9V on the other, the point where the two batteries are joined is the theoretical 'ground' of the batteries circuit. The TL072/TL074 IC chips used for this curve tracer use a 30 V supply split into +15 to ground and -15 to ground. Hope this explanation helps you understand Asle

David Marchesi

Of course but then you have no display, just a dot. Not very useful. Personally I don’t like playing the role of a sweep oscillator but that’s just me :)

Kuba Sunderland-Ober

The best way to lower noise in digital scopes is to enable bandwidth limiting on both channels, and perhaps add external gain so that you can use the 2V/div input attenuator setting. Some cheaper digital scopes cheat on attenuator settings and emulate some of them digitally without actually switching anything in the signal chain. That’s why for digital readout your best bet is either an Arduino dumping the data to a PC for real-time plotting, or a Parallax Propeller-based x-y to TV or VGA converter (Prop I and II will both work extremely well in this application). Digital scopes have bad 1/f noise that is pronounced at low frequencies. But for curve tracing you don’t want the frequency too high, or it will introduce artifacts in some circuits, while working better in others.

Kuba Sunderland-Ober

You need two separate power supplies (+15 V and -15V). You will need something like this except with 7815 and 7915 for 15V instead of 12V: https://circuitdigest.com/sites/default/files/circuitdiagram/12v-dual-power-supply-circuit-diagram.png

steve

Hi Paul, maybe this is a very stupid question, I want to build this curve tracer because I have got a couple of old oscilliscopes - BUT I am a little confused with the minus 15 volt. Is that the same as the minus from the power source, or do I need to have a separat power source that I connect to the minus 15 volt? And if so, what about the +15 volt from the other power source? To be short - what is the difference between ground and minus 15 volt? Can you (or some other guys who is smarter than me) explain me about this? 73 LB5JG Asle

Asle Runar Borgersen

I consider myself a beginning-to-start-to-commence-to-learn about-beginner. These videos are helping me a lot. Thanks, Paul, for your VERY THOROUGH teaching. Best money I spend all month.

Ross Hollinger

best cct ever

Michael Infante

Other question, the angle of the resistor footprint or signature, can you use that to determine the resistor value (Ohms)? Horizontal= infinite Ohms, Vertical= 0 Ohms ... 90 deg to devide all values in between

Tim Loo

Hi, I have a noob question, why use an oscillator to form the knees, when you can simply use a voltage regulator (albeit negative to positive) to dot down the knee position as you can see on the very low freq oscillation demo

Tim Loo

It’s possible that the diode you have is bad. Sometimes the entire lot may be bad. Or they may be counterfeit components. Decent Zeners have well defined, sharp knees.

Kuba Sunderland-Ober

Hi Edwin. The TL074 should not get hot. Make sure there is a clean sine at the output of the oscillator, no square-waving. Make sure your rails don't exceed 18 Volts + and - Use the lamp suggested or your results will vary.

Mr Carlson's Lab

I built this circuit after refurbishing a Knight KG-635 oscilloscope. I ended up using an LM324N for the TL074. I only had a TL074CN on hand and it almost immediately heated up, producing no ~1 KHz signal. I think the TL074CN would have melted if I had not turned off the power. I also breadboarded the TL074CN with just the oscillator circuit and it got smoking hot. Is there a circuit modification to stop the run-away internal oscillation (I'm guessing) of the TL074CN? Also, when I calibrate the ~1 Khz sine wave, maxing out the output control causes the signal to clip, regardless of the trimming pot setting. I am using a 56 ohm resistor to connect to the oscilloscope. I think the input of the Knight is being overloaded. Just sharing my experience; otherwise, the curve tracer works well.

Edwin Bindeman

Mr Carlson, I can't help but ask: where were you working when you showed this circuit to the engineers...?

Bruce Dow

You can Robert.

Mr Carlson's Lab

Hi Can I just use a function generator producing a 1 khz sine wave instead of the wien bridge oscillator? Thank You.

Robert M Radeski

Mr. Carlson, I have a couple of questions around the curve tracer circuit you have designed and built. I built the same thing. I am curious comparing the signal output between an analog scope and that of a digital scope such as a Rigol DS1054. The analog shows a better pictorial of the V vs I curve. While a digital scope is not as clean. Like you have mentioned on some of the digital scopes the noise it more pronounced. Question 1. How do you make the Curve Tracer Circuit show up better on a digital scope? Question 2. Experimenting with the frequency which I think going higher the digital scope shows up better, I know the lowest distortion for the TL071 OP Amp is at 1Khz, if you doubled or quadruple the frequency would that impact the function of the curve tracer and devices you measure with it?

Don Zanotti

Very nice stuff. I'm excited to the next building of the analog or digital display.

Escabusa Roy

Hi Toby. A vacuum tube curve tracer is on the list here. The differences between a tube and semiconductor tracer really isn't much, just Voltage and Current ratings differ. An FET is very close (in function) to a triode vacuum tube. Dual gate FET's act like tetrodes.

Mr Carlson's Lab

Mr Carlson, can you comment on the differences between a semiconductor curve tracer and one for electron tubes? If I wanted to match say 12AX7's. I assume tube curve tracer designs have been published many times, but I expect they use…tubes. Any chance of you doing such a project with modern components? :D

Toby

Great circuit here. Just a comment for other viewers: keep in mind that some zener can be tricky to identify. For example, using the curve tracer, 1N4738 (5.1V zener) shows reverse current before reaching -4V. I think this is because this diode requires higher currents to reach its nominal 5.1V. Mr Carlson could you please confirm that I'm right? I tested other smaller zener, and the knee is sharp and very close to nominal zener voltage. The trick for me right now is, if reverse voltage current is not sharp, then that voltage is probably (even) a couple of volts under nominal zener voltage.

David Senabre

Hi George. Analog scopes are pretty easy to use for this application, but if you have a newer digital scope, it will work as well. I think the analog scope displays this function nicer.

Mr Carlson's Lab

When looking for a used scope for this project, is it preferred to gave an analog or digital one ? I meant preferred as to ease to get working.

George Noyb

Thanks for challenging us to really think about the circuit at the end. I took a long time trying to figure out what it was doing. I used all my knowledge, and I guessed at some stuff, but I was rewarded when I watched the next video and found out I was right about a few things! I never would have tried to figure this out if you didn't challenge us, I would have just moved on to the explanation video. Great teacher!

Andrew Houck

Glad you got that supply, it sure is nice!

Mr Carlson's Lab

I got the power supply on Buy It Now... It looks like the same outfit has two more units for sale, so we can leave that link. :-)

Russ Sprouse

Looks good, and the price seems right. Dual 30V supply is nice to have on the bench.

Mr Carlson's Lab

Thanks, Paul! I also found this, it looks like a great power supply... Shall I jump on this too? <a href="https://www.ebay.com/itm/Instek-GPC-3030D-Triple-Output-Power-Supply-x2-30V-at-3A-and-5V-at-3A/291794403194?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D41376%26meid%3Ddf474dffd6fa4669b4cf62434adba0f8%26pid%3D100010%26rk%3D2%26rkt%3D6%26sd%3D202135770479&_trksid=p2047675.c100010.m2109" rel="nofollow noopener" target="_blank">https://www.ebay.com/itm/Instek-GPC-3030D-Triple-Output-Power-Supply-x2-30V-at-3A-and-5V-at-3A/291794403194?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D41376%26meid%3Ddf474dffd6fa4669b4cf62434adba0f8%26pid%3D100010%26rk%3D2%26rkt%3D6%26sd%3D202135770479&_trksid=p2047675.c100010.m2109</a>

Russ Sprouse

Jump on it.

Mr Carlson's Lab

What a beautiful machine! I think that says it all :^)

Mr Carlson's Lab

What do you think?

Russ Sprouse

Russ Sprouse

The TL072 is has a FET front end, where the others do not. They may be ok, just give them a try. I would try to stick to the original design though.

Mr Carlson's Lab

Hi Paul: You specify a TL072 or equivalent. I have some LM358N and MC1458 chips, Would either of these do the job? I'd like to breadboard the circuit and play with it driving my little digital scope, before I spring for a Tek 2236 on eBay.

Russ Sprouse

Hi Barrie. That really depends on the circuit. Decoupling caps are great in many applications and are needed, as you see, the circuit operates just fine the way it is, and in the circuit build as well, so I chose not to add them.

Mr Carlson's Lab

I noticed that you have not used decoupling capacitors across the supply rails on either the Wien Bridge or the Curve Tracer. I always thought that decoupling caps were essential with op amps. Should they be added or is it not necessary in these circuits?

Barrie Davis

Hey, glad to hear you have it working!

Mr Carlson's Lab

Thank you for your help again. I setup as you said using separate sig gen with still no Horizontal, vertical ok. I then noted the horizontal time was set to 100ns. I altered the time to 100ms and the Horizontal trace appeared. Learning all the time. again thanks and thanks for all the information. I am so grateful. I am 72 and just getting back into electronics after 55 years. and i am loving it. again Thanks Ps I didn't realise i had to set the time base on XY.

john smith

Hi John. That would indicate the Voltage follower isn't working. Before you try to troubleshoot the circuit, make sure the horizontal input on your scope is working. If you swap oscilloscope probes on the breadboard, when you ground the curve tracer probe, you should get a horizontal line.... Then swap the oscilloscope probes back, and the vertical should be normal again.

Mr Carlson's Lab

I am late with this help request. Back off holiday and trying to catch up, but is there anyone able to help me with a problem i am having with the circuit. I only have a digital scope (rigol ds1054z) and although i have checked the circuit many times i cannot get a horizontal trace. i get the vertical trace when i ground the probe. (when checked there is a sign wave on H and V) I cannot move on until i resolve this problem. I am new to electronics and my scope.

john smith

Thanks Reb, I appreciate it. I just saw this after posting above!

Psient

I'm not sure you mean this, but are you looking for a cheap analog scope on ebay? The curve tracer looked so so and updated slowly on my digital scope, so I purchased a Hitachi 2 channel analog scope for $27 on eBay. No bells or whistles, but it was cheap and seems to work well. It looks way better than the digital Rigol for displaying the curve tracer and random graphics using the XY.

jasper_fracture

I will try to be clearer. The costs I have found when trying to buy stuff recommended here is about 100 USD or more. The it-11 was about 200 USD tested. The Eico is 100 USD for parts untested beyond turning it on; a procedure you do not suggest as a risk of aggravation. I am saying that a budget of 50 bucks is good but seems unrealistic here in SoCal. I encourage others chiming in with more affordable alternatives.

Psient

I'm not sure I understand your question.

Mr Carlson's Lab

I am learning too. Eico on ebay + shipping = 1 C USDs not tested beyond electrification (turning-on)! What's an equivalent even at 200-300% Paul's cost . . . say .5 C USD . . . so as to employ this circuit?

Psient

Many Thanks Martin! Hadn't thought about AC and not using polarized caps (dumb) Everything working as it should now so will post in community.

Erik G

Unfortunately you wont be able to put any capacitor in the circuit because by design it is current limited. It is also AC so don't put a polarized cap in there, It should work with a small say 10nF ceramic type cap.

Smiggy

I suppose thats why some power supply schematics have a bulky 1 ohm 5 or 10 watt resistor in series with the output, for the current sensing for protection and/or current limiting.

Toni Pomar

Drat! mine doesn't work. Checked & treble checked wiring but only get voltage 'line' on digital oscilloscope. Plug in a probe short to ground (or a resistor to ground) and line disappears to a dot. Confused :-( Just one thought, do Wein Bridge & Curve tracer circuits need to share same power supply? Edit: by adjusting the Oscillator and Curve tracer pots a bit, I can get the horizontal line to change to a vertical when shorted and a resistor inserted gives me a diagonal (depending on the resistance value). A capacitor however does not give me an 'ellipsoid :-/

Erik G

This has been a great learning experience for me - very much enjoyed it, thanks to you all. Also found a link/article to a similar circuit in case anyone is interested: <a href="http://www.eeweb.com/blog/extreme_circuits/curve-tracer-adaptor" rel="nofollow noopener" target="_blank">http://www.eeweb.com/blog/extreme_circuits/curve-tracer-adaptor</a>

jasper_fracture

A major application of current sensing is protection. There are many instances where a design engineer will want to trip the power supply on an over current event, your tv for example. To do this it will require some means of measuring and detecting an over current event. The high side low side is where you would place the sensing resistor in the circuit. The circuit Paul has developed we want to limit the current and measure it, there is already some limiting because the oscillator op amp can only deliver a certain amount of current. Toni has already calculated the worst case event, short circuit the probe so all being well under no circumstance should your shack be filled with a smoke event! From ohms law you know that the current through a resistor is proportional to the 'difference' in voltage across the resistor and the resistor value, the signal from the bottom 'differential' op amp is fed to your oscilloscope to indicate the changes in current.

Smiggy

Great analysis work Toni. Doing some reading I see there is high and low side current sensing, is this related to what we are seeing.

Hunter carmouche

Thanks, been scratching my head for days on this one. Can't wait either for the next video :-)

Toni Pomar

Well done you are the winner, I am sure Paul will go through some of the finer points about the circuit in the next video. Cannot wait :-)

Smiggy

All good tries Hunter!

Mr Carlson's Lab

Good stuff Toni! I will explain more about this in the next upcoming video.

Mr Carlson's Lab

So the 7k resistor is the "current sensor" that limits the current and "converts" it into a differential voltage for the amplifier that drives the Vertical trace. As the output of the wien oscillator is 20Vpp, and the lowest input impedance possible (when the probe is shorted to ground) is 7k, that means a maximum current of 1.4mA through the resistor, and through any probed component. About the value, it seems to be chosen as to not to alter too much the parameters of the amplifier (7k is 1/60 the impedance of the upper branch of the amplifier), or maybe is a more sofisticated math that I don't see right now ;)

Toni Pomar

The sine Current, is going through something that's limiting it.

Mr Carlson's Lab

Do you mean..... Whats limiting that Current? :^)

Mr Carlson's Lab

How is the AC current getting from your 1kHz oscillator to the component under test?

Smiggy

So with the rules of op amps applied, infinite input resistance, zero input current, is the current going through the feedback resistor??

Hunter carmouche

Check Martin's post below..... some hints there.

Mr Carlson's Lab

Ahh Ha! Now I see the grey matter working!

Mr Carlson's Lab

If you only had a volt meter how would you measure and calculate the current? Paul demonstrated that with the 'probe' open circuit, 'no current flow' condition it was volts only from the oscillator being measured horizontal trace via the top op-amp H. With the 'probe' short circuit 'no volts across the component' condition it was only current from the oscillator being measured vertical trace via the bottom op-amp V.

Smiggy

Thanks Martin, I was trying to make it harder than it was. That sounds really good also jasper. Have feeling it's going to be a combination.

Hunter carmouche

I'll take a shot at it...please forgive any noob mistakes. The first opamp looks like a noninverting unity gain configuration which outputs the x coordinate. The second opamp looks like a differential configuration which outputs the y coordinate (??). The 7.15K to 7.5K resistor helps set the gain of the differential op amp at pins 5,6,7 (??)

jasper_fracture

I love it Hunter, the xy plot is a voltage verses current graph, V-I graph (yeah the letter I for current something to do with a French bloke called Ampere) so we need to have the voltage across and a voltage representation of the current through the component under test for the scope input

Smiggy

Ok, Good try #3. Does it keep the loop gain negative so you'll have a closed loop gain at infinity, hence will not let the oscillations die out. I know this is it, I can feel it.

Hunter carmouche

Keep trying Hunter. We'll say the first two don't count ;^)

Mr Carlson's Lab

Ok, Good try #2. With the spirit of Welcome Back Kotter while raising my hand ooh! ooh! ooh! Because resistors are not equal you took the parallel value of the 220k resistors and maybe the 150 and also the VR and got a total. You then multiplied that by 1/10 and came up with the 7.15 value.

Hunter carmouche

Thanks Leland!

Mr Carlson's Lab

Down the road, yes. The addition of a "step generator" would make this unit a different animal. This is designed for in circuit testing, where as the 501 is a dedicated "stepped curve tracer"

Mr Carlson's Lab

Glad to share Phil!

Mr Carlson's Lab

Good try Hunter, but unfortunately, no.

Mr Carlson's Lab

Ok, I'll take a stab at the question at the end of the vid. 7.15 resistor, CMRR, compensating for noise between inputs.

Hunter carmouche

+15V/-15V supply. I have both the WBO and the curve tracer on the same board sharing the same supply....or, did you mean the internal bits of the 072?

jasper_fracture

Does anyone know what the +Vcc and -Vcc pins (4+8) are wired to in the TL072 dual Op-Amp chip? Thx.

Stephen Martin

Are there any plans to make it work in a similar fashion to a B&K 501? I would like to make something with that sort of functionality.

Eddie Bray

Paul... Great video. This circuit is really useful. I have tested a few zeners of the same rating and the curves vary quite a bit more than I would have expected. Thanks for sharing this gem with us!

nj Phil

Thanks to you, Eddie, and also Colin for your replies. I am sorry to seem so blind, but having just recently joined the group, I am still struggling to learn all of the details of this group. Where do I find the community section and specifically your poster schematic? Thanks for your help.

Steven Munts

Hi Gregg. That really depends on the power supply design. The item your testing should be un-plugged and the batteries removed before using the curve tracer for in circuit testing.

Mr Carlson's Lab

Thank you for this very interesting build. Quick question, should I have the power supply for this plugged into an isolation transformer? Once again, thank you!

Gregg Adams

Glad you're enjoying Carl!

Mr Carlson's Lab

That's a great scope! I'm "Very" glad you made that purchase, rather than going with the other.

Mr Carlson's Lab

Here it is Tom: <a href="https://www.patreon.com/posts/build-this-low-11523102">https://www.patreon.com/posts/build-this-low-11523102</a> You can find this in the "posts" section. When you log in, you will be on the main page, just scroll down to see the entire list of video's.

Mr Carlson's Lab

Hi George, I would go for a 100Mhz scope, they are reasonably priced now, and you won't find as many limitations.

Mr Carlson's Lab

This should only be used on a circuit that has no power applied, as the curve tracer is supplying the Voltage/Current.

Mr Carlson's Lab

Great job Paul and Tom above is correct, but I have used Alan's work for over a year to sort thru parts and have been very satisfied. What I really find exciting is your next promised edition to enhance the curve tracer. Thanks for your hard work.

Carl Davis

So far you are accomplishing what you are seemingly motivated towards, at leazt with me. Thank you for the continued lessons. Us beginners have to be fit in order to keep up with the excellence of your diverse and effective community. Hustling as fast as I can to get there. Just made a purchase of the DS1054Z, so I can follow along. You fellows are such a big source and an assist.

Psient

Paul, I looked for a video on the wein bridge oscillator. Did you do one and I can't find it? I would like the schematic. I built the 'octopus circuit tester' from Alan, W2AEW but yours is more elegant and works much better!

Tom Bilello

I know nothing about scopes. Look on ebay I see some very low prices on analog scopes. My main interest will be old tube amps and radios plus whatever projects happen here. Question is what Mhz should I be looking at? Thanks for any suggestions.

George Myers

Awesome work Paul. Can't wait for the digital monitor for the circuit.

Leland Clayton

Paul, et al,maybe missed this, but does this work with an activated circuit (i.e., voltage/power applied) or passive (no voltage)?

William Phinizy

Use Eddies schematic with the LM7815 / LM7915 voltage regulators .. I forgot that they had 15v versions.

Colin Hawke

I have posted a schematic in the community section which should help.

Eddie Bray

Sorry no schematic. The simplest way probably would be to use the LM317T and LM337T voltage regulators. You'll need to choose the correct resistors for the adj pins to get postitive & negative 15v. Input would come from a centre tapped transformer that is rectified and smoothed.

Colin Hawke

Does anyone have a good reliable schematic for a 15-0-15 volt power supply? Either a schematic, link or source would be greatly appreciated. Thanks in advance.

Steven Munts