Alan Wolke, you are amazing person! ... Iam now 45yo ... but watching your videos is fulfilling my dreams about electronics from my childhood. Finally I found your lectures!
This video is still relevant in oct '23. I found some regular opamps in one of my bins, so I ordered the required r2r opamps and I will be building this circuit soon, just for fun and education.
If the school teachers are as motivated and interesting as you are, we would have an army of young radio/electronics enthusiasts. Well done Alan! Good on ya mate!!!
What a refreshing video, to see an oscillator in this day and age that's not some super integrated proprietary PLL kind of deal or a microcontroller running one line of code is just very pleasant.
Great little tutorial on this interesting circuit. It's a very visual circuit on the scope as well; so that makes it more educational to visualize what is happening. Thanks for all your great vids.
+w2aew please man make a video on analog sinusoidal generators something simple like you made in the video Simple 3 transistor sawtooth generator / oscillator no DDS i need something from ,,0``-6 Mhz or 0-1 Mhz and explain it like you done it on that video
Impatient to try this but waiting for rail to rail op amps to arrive...tried LM324. Got the relaxation oscillator running and adjusted pulse timings. Then the 555 pulse generator and added the reset. More adjustment to get about 12 steps between resets. Then added the pulse integrator but results were not as expected. Reset was not taking the integrator capacitor to ground. Eventually figured out that the 8k2 base resistor needed to be reduced to turn on a 2N3904 sufficiently to get down to ground during a reset. Guess this is a consequence of not using a rail to rail op amp. More adjustment of the base drive and finally an output close to yours. Not quite as square steps but close. Spent a few hours working on this circuit because it looked fascinating and have learnt lots about basic electronics. There is no substitute for doing - great that your videos are, there is even more to be gained by building and modifying. Been great fun and learning.
+The Current Source I do as well! I have 2 night rider circuits running right now just for my pleasure; an analog circuit with the venerable 555, 4017, and a bunch of diodes, and one using an Arduino. I prefer the analog circuit because it just seems to me to be warmer and more fluid than the digital Arduino circuit. Is it just me?
I will give that a go ! This has got to be one of those few times when i wanted a circuit that does more with simple parts and better than i could of expected ...all the links very very helpful thank you !
Very interesting as usual and a little over my head at times - lol Well presented valuable training. Thank you for providing it and Keep up the great work!
A little something for the first oscillator is you can use a linear pot and 2 diodes in the feedback network so you can have a near constant frequency ( roughly, you will have to vary C to get different frequencies) but where the duty cycle is variable over a very wide range, from around 5% to 95% as you turn the knob. Can be used with the whole circuit to sample the output to get a specific step using a differentiator driving a sample gate ( 4066 switch). But I can see a use for an analogue staircase generator where you can select the number of steps easily just by using RC delays.
Hi Alan, It reminds me of the basis of a transistor curse tracer on an oscilloscope of the 70's, when at school. It could be a "fun circuit" to see you build :-). Your videos are greatly instructive. Thank you for share so much knowledge with us. Regards, RJM.
Neat circuit! BTW that output stage is called a Deboo integrator, one of an interesting class based on Howland current sources. It's great for single-supply as it's non-inverting, unlike conventional Miller integrators.
Very nice little circuit. If you put about a 47K resistor on the base of Q2/Q1 to ground, it'll work better with 2N2222 transistors - they tend not to turn off very fast and hold the 555 in reset too long so you only get 4 or 5 steps out of it. Just a thought :) Love your videos.
Thank you! Your videos always inspire me to experiment with LTspice. I made one with transistors only containing just a single oscillator. Works in LTspice, but I don't know if it works in real life. :D
+RF Burns Playing around on the bench, I managed to turn it into a basic transistor curve tracer by adding one more op amp, 3 more transistors and a handful of passives... Maybe I'll post another video...
the reseting op amp may be another 555 timer .. I have too much ot this buggers and that would i do.. Everyone can adapt the circuit with his own view .. The final op am is neat ! Great job
This reminds me of a AGC circuit I stumbled into building on breadboard about 30 years ago... The accumulator drove attenuators, a detector drove the accumulator, and a timer reset it to detector level after the hang time. Fast attack, no pumping, fixed hang time; for something so crude it worked great. Sadly I've long lost the schematic I drew.
I use a LM358 as OPAM ( i have no "rail to rail" one) and I need to put a diode between 8k2 resistor and transistor bases in orden to achive transistors off state. So I get a nice stairstep.
Thanks for your awesome training techniques they are very clear and understanding. Have you ever experience any three phase circuits to parallel AC generators, or do you have any ideas on what chip should be use for phasing sequence two or more AC generators
There is a bar on top of the reset pin on the diagram, which means it is an active low reset, which means the reset is default high. When there is a low, the circuit resets. But your scope is showing an active high reset - whenever the pulse is high, it resets.
I thing you can automate it by letting the relaxation oscillator making the high frequency pwm and let the 555 in monoflop configuration which gets triggered by a high at out to make the discharging step at the output.
Really nice video. IMHO had the right amount of content and some nicely paced descriptions. Just the right level for me. I was wondering... does it need an output buffer... any load will disrupt the stairstep? Also, it's a nice old school design but isn't it actually cheaper nowadays to use a small pin-count controller?
+NivagSwerdna The op amp used in the pulse integrator has a low impedance output, so no need for buffer. Of course, it would likely be cheaper to use a cheap uC to do this, but - it would need to be programmed, and you wouldn't learn about the cool analog circuitry. What fun is that? ;-)
As always great explanation. I'm assuming this circuit must have a lower frequency boundary? on the basis that the step will decay and there will be a point where the sag makes this too nonlinear, is this right?
Dear Sir, Yes, absolutely. I am trying that but I am learning and use capture, compare of PWM, but at the age of 55, it is little too much to learn, so I felt if you have any solution I would implement it. In fact I do not need the DAC, as I just want to generate thyristor firing pulses for Phase angle control of thyristor from simple PID time-proportional output of the temperature controller. Anay ways thank you very much for your attention.
Probably a stupid question here, but as a newbie, can I use my op amp oscillator in place of the 555? If so what modifications would you need to make? I have limited access to materials at the moment.
I got it going but got some extra lines. Is 50mhz Rigol scope fast enough?? On another note I held a match to the DUT and watched the curves rise and fall, that was cool.
Your tektronix mdo4104c oscilloscope - where would be a good place to find such a scope? I have seen some for $17k to $23 which is too high for a hobbyist like my self. Could you recommend a similar but less expensive scope?
Hi Alan, As always,your content and presentation skills are absolutely impeccable !! Hope I did not miss it,but could you clarify why you have the 6k8 resistor to ground on the output of U1. TIA.
+EmbSysDev You didn't miss anything. I was experimenting with a couple of different op amps, and some of them worked better with a pull-down resistor. This op amp doesn't need it. So, it really could be eliminated without any peril.
In my case, the circuit didn't work until I added this resistor. In fact, the stairstep looked all wrong at first until I brought this resistor down to 1K which made it much better. It is still a very noisy plot, it seems like the output of the 555 gets all noisy as soon as I connect it to the op amp. Still investigating how to get it clean as Alan's graphs on the scope.
What is the purpose of the 6.8 kOm resistor, used in the Schmitt trigger relaxation oscillator circuit, connected between opamp output and ground? From threshold voltage point of view, this resistor is unnecessary - it does not change Vth+ nor Vth-. It only loads opamp output with more current.
The circuit was originally designed using an op amp whose output stage would add crossover distortion when swinging to the rail due to the design of its push-pull output stage. The resistor to ground kept the output stage in Class A. You're right, not needed with this particular op amp.
You are a great teacher! I'm curious: what applications would you use a staircase generator or signal? I seem to recall part of the old NTSC color TV signal having one?
+agentsmithisalive Let me give a big old "/me too"' to this comment. From the previous comments I can guess it would be used in a curve tracer but just a couple lines in the video about what they are used for would have been really helpful for people like me who admire the beauty and cleverness of the circuit but wonder why one would build it.
+agentsmithisalive Playing around on the bench, I managed to turn it into a basic transistor curve tracer by adding one more op amp, 3 more transistors and a handful of passives... Maybe I'll post another video...
+llhand Playing around on the bench, I managed to turn it into a basic transistor curve tracer by adding one more op amp, 3 more transistors and a handful of passives... Maybe I'll post another video...
+w2aew That would be great -- would love to see a curve tracer! BTW, I was partially correct: it's the NTSC *monochrome* signal that uses a stair-step pattern (for the luminance signal). See: www.eetimes.com/document.asp?doc_id=1272387 Thanks again and 73!
Great circuit. Love your videos. As I know that using a transistor to discharge a capacitor periodically is pretty standard I like to know a little bit more about it. In this circuit Q2 is discharging the 0.1uF capacitor. My question is this; Is the current through the transistor limited by the emitter resistance (~25 Ohm) or by something else (I am presuming it is limited by something). The reason I am asking is that, given a finite current you would need a minimum pulse width to discharge the capacitor. Also, am I right in thinking that the capacitor only discharges to about 0.2V, being the collector-emitter voltage of a saturated transistor? Thank you very much for making these great videos.
Probably answering my own question, but I realised the "transistor action" rule: Ic = Ib * beta So given a Vcc of 9V there will be a base current of about 1mA (8.3V/8k2Ohm). With a beta of 100 this would drain the capacitor with 100mA. Thus the time to drop the capacitor voltage from 9V to 0V will be 9V*0.1uF/100mA = 9us. Did I do this right?
+Alwin Leerling Yep - that's basically it. Of course, once the transistor reaches saturation, the beta drops. And, as you said, it's only getting discharged to the VCEsat of the transistor. For our purposes here, it works just fine.
Youre great and your final output stairstep* wave/signal is worth goldif it is possible to make this work in the 400V-1200V range, it is because the wave form is exactly right for a Quasi continues wave tesla coil!! So my question is how to amplify it even more? * :)
The staircase waveform looks linear on the oscilloscope (before the "steps" are carved into it). However, the main capacitor is charged by a 10k resistor on the output of the 555, rather than by a current source, so I would expect it to be exponential. Maybe it is actually exponential, but just doesn't appear to be so, or have I misunderstood something?
Does the output stage need to be as complex? Could we just have a diode from 555 output -> capacitor positive side then put a buffer/voltage-follower there?
Hey i am a noob on the matter but i still found this quite fascinating and interesting. Though i'm trying to understand what from your expert perspective and knowledge about electronics is fun about this circuit? i got a sense that it is because it's performing an action without memory but by its own diagram? is that what's special about this? thank you for any reply and nice video
+Francesco Laurenti The typical way to create a stairstep waveform would be with a counter and a digital to analog converter. I thought this was interesting (fun) because it uses just a pair of astable pulse generators and a pretty unique integrator circuit (Deboo Integrator) to create the steps. I hadn't seen this configuration of integrator before and thought it was quite interesting.
Sorry to bother you again but I have another question. In the reset circuit, what is the function of the 6.8k resistor between the op-amp output and ground? I breadboarded just this part and played around with the resistor. The only thing I noticed was a slight level increase of the pulse when I disconnect the resistor. Thank you in advance.
+Alwin Leerling Not really needed. I was playing with a couple of different op amps, and a few needed a pull down to completely shut off the transistors. With many rail-rail op amps, this resistor isn't needed anymore.
+Vale Sarbu Both transistors are turned on "hard", meaning both are going into saturation. No special matching needed in this case - just use the same type of transistor. Of course, you could simply use one more resistor to drive each base independently from the reset pulse generator.
Some are my own, some are circuits I've seen elsewhere, or based on circuits seen elsewhere. Some are adaptations of circuits I've seen, or even circuits shared with me by friends.
I have a Heathkit IG-1275 Log/Lin Sweep Generator. I would like to display markers, say 10 marks both Log and Linear, across the X axis on an Oscilloscope using the scopes Z axis input to show the marks. Is this possible to display marks both linear and logarithmic across the X axis using the Sweep Gate Output, Sweep Output, or Analog Output of the IG-1275 using the Step Generator circuit #231?
+Gregory Burns You probably only need the 555 pulses. Reset the 555 at the start of the sweep, and then adjust the period of the 555 pulses to get the timing that you need. Of course, this will only work with the Linear sweep. For the log sweep - maybe multiple window comparators to detect the sweep voltage at various thresholds...
So if you make the 555 pulses wider, that means more time to increase the capacitor voltage so the steps would have a bigger voltage difference between?
Hi, After time domain, let's go to frequency domain.. So could you make a video about making a "frequency staistep" for a spectrum analyzer ? Thank's ! May be Mr Carlson's could do this too.. Who will be the first to challenge this ?
Hi I like these kind of videos just wondring if i can give you a veroboard ver that i have done for this circuit To help others that might want to make this. I have had fun making this on veroboard over the weekend. Thanks for reading
I have downloaded 99% of your videos and for this one I ran LTspice SImulation and got the same results. Would like to email you the Document I created for it but need an email address to send you the document for your review and also the simulation file? Thank you for sharing your knowledge and making my day
+freqcy The best thing to do would be to post the files online somewhere (Google Drive, etc.), and then post the link here - that way, everyone can benefit from your work.
Alan Wolke, you are amazing person! ... Iam now 45yo ... but watching your videos is fulfilling my dreams about electronics from my childhood. Finally I found your lectures!
I love the style of your videos - it's almost a cliché, but it really is like having a great teacher sit next to you and explain stuff. Thank you.
This video is still relevant in oct '23. I found some regular opamps in one of my bins, so I ordered the required r2r opamps and I will be building this circuit soon, just for fun and education.
The way you explain these circuits is engaging even for a novice like me. Using the scope as a demonsration is icing on the cake. Thanks!
If the school teachers are as motivated and interesting as you are, we would have an army of young radio/electronics enthusiasts. Well done Alan! Good on ya mate!!!
Thanks so much. It's my new years resolution to build and describe 20 circuits. I may give the stairstep generator a shot!
Bravo! In all the time I've been following YT, I've only found two such excellent educators. You and DiodeGoneWild.
Couldn't agree more !
What a refreshing video, to see an oscillator in this day and age that's not some super integrated proprietary PLL kind of deal or a microcontroller running one line of code is just very pleasant.
+FFcossag I have a lot of oscillators that are uC and PLL free on this channel ;-)
***** Crap, I just got busted as a really bad subscriber for not knowing that, didn't I?
Not at all, with over 230 videos, you can certainly be excused for not knowing everything that's here. Thanks for being a subscriber.
Great little tutorial on this interesting circuit. It's a very visual circuit on the scope as well; so that makes it more educational to visualize what is happening. Thanks for all your great vids.
This is a great reason to get the breadboard out...cheers
Nice circuit analysis Alan.
Thanks for your time to build it on breadboard...
My new favorite YT channel. This is amazing!!! Thank you so much for taking the time!
73 N0BPS
+Brian Streufert Thank you - I hope you enjoy my other 230 videos just as much!
+w2aew please man make a video on analog sinusoidal generators something simple like you made in the video Simple 3 transistor sawtooth generator / oscillator no DDS i need something from ,,0``-6 Mhz or 0-1 Mhz and explain it like you done it on that video
Impatient to try this but waiting for rail to rail op amps to arrive...tried LM324. Got the relaxation oscillator running and adjusted pulse timings. Then the 555 pulse generator and added the reset. More adjustment to get about 12 steps between resets. Then added the pulse integrator but results were not as expected. Reset was not taking the integrator capacitor to ground. Eventually figured out that the 8k2 base resistor needed to be reduced to turn on a 2N3904 sufficiently to get down to ground during a reset. Guess this is a consequence of not using a rail to rail op amp. More adjustment of the base drive and finally an output close to yours. Not quite as square steps but close.
Spent a few hours working on this circuit because it looked fascinating and have learnt lots about basic electronics. There is no substitute for doing - great that your videos are, there is even more to be gained by building and modifying. Been great fun and learning.
I *LOVE* to hear when my videos inspire folks to build, experiment, test, and learn!!! Thank you!
Beautifully explained as usual. Love the analog stuff
+The Current Source I do as well! I have 2 night rider circuits running right now just for my pleasure; an analog circuit with the venerable 555, 4017, and a bunch of diodes, and one using an Arduino. I prefer the analog circuit because it just seems to me to be warmer and more fluid than the digital Arduino circuit. Is it just me?
I will give that a go ! This has got to be one of those few times when i wanted a circuit that does more with simple parts and better than i could of expected ...all the links very very helpful thank you !
That's a pretty elegant circuit, thanks.
Such an amazing circuit.. ties in a lot of concepts together.. great for learning
Great video. This works really well with swapping out the 555s and op amp with 15ms trigger clocks for CV generation for electronic music gear.
This was just plain fun. Well done as always. Thanks a lot Alan.
Thank you for providing the schematic. I'm going to print it out and put it on my wall.
Oh.... that's what the RESET pin is for! Still learning. Great video as always and thanks for the education!
Very interesting as usual and a little over my head at times - lol
Well presented valuable training. Thank you for providing it and Keep up the great work!
Always nice to Watch and have the schematic besides. Many could learn from the way you do.
A little something for the first oscillator is you can use a linear pot and 2 diodes in the feedback network so you can have a near constant frequency ( roughly, you will have to vary C to get different frequencies) but where the duty cycle is variable over a very wide range, from around 5% to 95% as you turn the knob.
Can be used with the whole circuit to sample the output to get a specific step using a differentiator driving a sample gate ( 4066 switch). But I can see a use for an analogue staircase generator where you can select the number of steps easily just by using RC delays.
+SeanBZA Thaks - that's the whole idea here - just get folks thinking about the possibilities, and other circuit ideas.
Hi Alan, It reminds me of the basis of a transistor curse tracer on an oscilloscope of the 70's, when at school. It could be a "fun circuit" to see you build :-). Your videos are greatly instructive. Thank you for share so much knowledge with us. Regards, RJM.
Did you check the next video in series? I did make a basic transistor curve tracer using this:
ua-cam.com/video/ZOLLoa2fH24/v-deo.html
Beautiful circuit, and crystalclear explanation. Thanks for sharing!
Neat circuit! BTW that output stage is called a Deboo integrator, one of an interesting class based on Howland current sources. It's great for single-supply as it's non-inverting, unlike conventional Miller integrators.
Oh, excellent! I didn't know there was a name for it. I see now that Maxim has some application notes on it. Nice! Thanks for sharing!
جزاك الله خيرا وزادك علما والله اكبر
Allen thanks for doing these videos, great job
+joel hall ment Alan,sorry
Very clearly explained as usual- I am playing with a similar stair-step circuit for use as an analog frequency divider
thanks - I have to add one of these to the system I am currently designing and this video really made the analysis simple
Awesome video Alan. thanks for posting
Very nice little circuit. If you put about a 47K resistor on the base of Q2/Q1 to ground, it'll work better with 2N2222 transistors - they tend not to turn off very fast and hold the 555 in reset too long so you only get 4 or 5 steps out of it. Just a thought :) Love your videos.
Thank you! Your videos always inspire me to experiment with LTspice. I made one with transistors only containing just a single oscillator. Works in LTspice, but I don't know if it works in real life. :D
Sounds like you'll have to go build it and see!
Nice lesson as always Alan! It will be interesting to see what I can do with it controlling the reset pin with resistance rather than voltage.
Again a great lesson..happy and healthy 2020
Very interesting circuit, and Great Video. Thanks for sharing.
Really awesome circuit analysis! Thanks.
I really do enjoy your circuit analysis videos. Are there future plans for this circuit? - A video linearity tester? - A transistor curve tracer?
+RF Burns No plans yet - but using as a start on a curve tracer did cross my mind...
*****
I would love to see that! And perhaps build for myself.
+RF Burns Playing around on the bench, I managed to turn it into a basic transistor curve tracer by adding one more op amp, 3 more transistors and a handful of passives... Maybe I'll post another video...
*****
Cool! Can't wait!
Great video content as usual. Thank you.
A very great explanation - perfect job!
the reseting op amp may be another 555 timer .. I have too much ot this buggers and that would i do.. Everyone can adapt the circuit with his own view .. The final op am is neat ! Great job
As always ... Great job. Wonderfull explanation. Thank you.
very very interesting circuit. thank you
Seems like a 556'd be a good fit too :) fun stuff
simply beautiful.
*Vielen Dank* für Deine wunderbaren Videos!
Bitte schön
What a master piece!!
Love this! Please do more videos like this if you can!
Thanks for easy to understand review, as usual :-)
Nice video once again! Fun circuit, clear explanation, as usuaL, Thanks! I see many potential uses, gives me ideas!.
+jeromekerngarcia Perfect - glad to be an inspiration!
Thank you, it's very interesting video. I wanna watch your videos on analog circuits from basic to the one more complicated.
Wow, this is amazing - got to go build one!
Your schematics are very neat !
Another enjoyable video. Thank you! Would it be possible to ramp down instead of up? or even more daring, ramp both up and down like a triangle wave?
Amazing explanation!
This reminds me of a AGC circuit I stumbled into building on breadboard about 30 years ago... The accumulator drove attenuators, a detector drove the accumulator, and a timer reset it to detector level after the hang time. Fast attack, no pumping, fixed hang time; for something so crude it worked great. Sadly I've long lost the schematic I drew.
+ZlayaCo6aka Say it ain't so!
I use a LM358 as OPAM ( i have no "rail to rail" one) and I need to put a diode between 8k2 resistor and transistor bases in orden to achive transistors off state. So I get a nice stairstep.
Still a great watch!
Thanks for your awesome training techniques they are very clear and understanding. Have you ever experience any three phase circuits to parallel AC generators, or do you have any ideas on what chip should be use for phasing sequence two or more AC generators
I'm sorry, I really don't have any experience with 3-phase power circuits.
There is a bar on top of the reset pin on the diagram, which means it is an active low reset, which means the reset is default high. When there is a low, the circuit resets.
But your scope is showing an active high reset - whenever the pulse is high, it resets.
When the pulse goes high, it turns on Q1 which pulls the reset pin low. Q1 inverts the signal.
Ooo, I like this a lot! Simple components and design is sexy! I wonder how it sounds...
That's very look like a kind of flip-flop circuit! Very awesome how you do without memory circuit or microcontroller! THK!
I thing you can automate it by letting the relaxation oscillator making the high frequency pwm and let the 555 in monoflop configuration which gets triggered by a high at out to make the discharging step at the output.
very informative and very interesting video. I like your channel.
Really nice video. IMHO had the right amount of content and some nicely paced descriptions. Just the right level for me.
I was wondering... does it need an output buffer... any load will disrupt the stairstep? Also, it's a nice old school design but isn't it actually cheaper nowadays to use a small pin-count controller?
+NivagSwerdna The op amp used in the pulse integrator has a low impedance output, so no need for buffer. Of course, it would likely be cheaper to use a cheap uC to do this, but - it would need to be programmed, and you wouldn't learn about the cool analog circuitry. What fun is that? ;-)
Like you voice over circuit analyzing technique.
Reminds me of the old days of CRTs...
I like your excellent explanations.....well done...!!!!
As always great explanation. I'm assuming this circuit must have a lower frequency boundary? on the basis that the step will decay and there will be a point where the sag makes this too nonlinear, is this right?
Yes, that is correct.
Would be nice to see this circuit actually doing something
As always great! Awesome!
Thanks a lot!
Dear Sir,
Yes, absolutely. I am trying that but I am learning and use capture, compare of PWM, but at the age of 55, it is little too much to learn, so I felt if you have any solution I would implement it. In fact I do not need the DAC, as I just want to generate thyristor firing pulses for Phase angle control of thyristor from simple PID time-proportional output of the temperature controller.
Anay ways thank you very much for your attention.
Probably a stupid question here, but as a newbie, can I use my op amp oscillator in place of the 555? If so what modifications would you need to make? I have limited access to materials at the moment.
I got it going but got some extra lines. Is 50mhz Rigol scope fast enough?? On another note I held a match to the DUT and watched the curves rise and fall, that was cool.
Sure - this is a pretty slow circuit.
Your tektronix mdo4104c oscilloscope - where would be a good place to find such a scope?
I have seen some for $17k to $23 which is too high for a hobbyist like my self. Could you recommend a similar but less expensive scope?
Hi Alan,
As always,your content and presentation skills are absolutely impeccable !!
Hope I did not miss it,but could you clarify why you have the 6k8 resistor to ground on the output of U1.
TIA.
+EmbSysDev You didn't miss anything. I was experimenting with a couple of different op amps, and some of them worked better with a pull-down resistor. This op amp doesn't need it. So, it really could be eliminated without any peril.
In my case, the circuit didn't work until I added this resistor. In fact, the stairstep looked all wrong at first until I brought this resistor down to 1K which made it much better. It is still a very noisy plot, it seems like the output of the 555 gets all noisy as soon as I connect it to the op amp. Still investigating how to get it clean as Alan's graphs on the scope.
What is the purpose of the 6.8 kOm resistor, used in the Schmitt trigger relaxation oscillator circuit, connected between opamp output and ground? From threshold voltage point of view, this resistor is unnecessary - it does not change Vth+ nor Vth-. It only loads opamp output with more current.
The circuit was originally designed using an op amp whose output stage would add crossover distortion when swinging to the rail due to the design of its push-pull output stage. The resistor to ground kept the output stage in Class A. You're right, not needed with this particular op amp.
@@w2aew Thanks for explanation.
You are a great teacher! I'm curious: what applications would you use a staircase generator or signal? I seem to recall part of the old NTSC color TV signal having one?
+agentsmithisalive Let me give a big old "/me too"' to this comment. From the previous comments I can guess it would be used in a curve tracer but just a couple lines in the video about what they are used for would have been really helpful for people like me who admire the beauty and cleverness of the circuit but wonder why one would build it.
+agentsmithisalive Playing around on the bench, I managed to turn it into a basic transistor curve tracer by adding one more op amp, 3 more transistors and a handful of passives... Maybe I'll post another video...
+llhand Playing around on the bench, I managed to turn it into a basic transistor curve tracer by adding one more op amp, 3 more transistors and a handful of passives... Maybe I'll post another video...
+w2aew That would be great -- would love to see a curve tracer! BTW, I was partially correct: it's the NTSC *monochrome* signal that uses a stair-step pattern (for the luminance signal). See: www.eetimes.com/document.asp?doc_id=1272387 Thanks again and 73!
Great circuit. Love your videos.
As I know that using a transistor to discharge a capacitor periodically is pretty standard I like to know a little bit more about it.
In this circuit Q2 is discharging the 0.1uF capacitor.
My question is this; Is the current through the transistor limited by the emitter resistance (~25 Ohm) or
by something else (I am presuming it is limited by something).
The reason I am asking is that, given a finite current you would need a minimum pulse width to discharge the capacitor.
Also, am I right in thinking that the capacitor only discharges to about 0.2V, being the collector-emitter voltage of a saturated transistor?
Thank you very much for making these great videos.
Probably answering my own question, but I realised the "transistor action" rule: Ic = Ib * beta
So given a Vcc of 9V there will be a base current of about 1mA (8.3V/8k2Ohm). With a beta of 100
this would drain the capacitor with 100mA. Thus the time to drop the capacitor voltage from 9V to 0V
will be 9V*0.1uF/100mA = 9us.
Did I do this right?
+Alwin Leerling Yep - that's basically it. Of course, once the transistor reaches saturation, the beta drops. And, as you said, it's only getting discharged to the VCEsat of the transistor. For our purposes here, it works just fine.
Youre great and your final output stairstep* wave/signal is worth goldif it is possible to make this work in the 400V-1200V range, it is because the wave form is exactly right for a Quasi continues wave tesla coil!! So my question is how to amplify it even more? * :)
The staircase waveform looks linear on the oscilloscope (before the "steps" are carved into it). However, the main capacitor is charged by a 10k resistor on the output of the 555, rather than by a current source, so I would expect it to be exponential. Maybe it is actually exponential, but just doesn't appear to be so, or have I misunderstood something?
This iş What I also getting 1 volt straight line don't know what is wrong
Does the output stage need to be as complex? Could we just have a diode from 555 output -> capacitor positive side then put a buffer/voltage-follower there?
Hey i am a noob on the matter but i still found this quite fascinating and interesting. Though i'm trying to understand what from your expert perspective and knowledge about electronics is fun about this circuit? i got a sense that it is because it's performing an action without memory but by its own diagram? is that what's special about this? thank you for any reply and nice video
+Francesco Laurenti The typical way to create a stairstep waveform would be with a counter and a digital to analog converter. I thought this was interesting (fun) because it uses just a pair of astable pulse generators and a pretty unique integrator circuit (Deboo Integrator) to create the steps. I hadn't seen this configuration of integrator before and thought it was quite interesting.
Could the circuit at 2:19 be modified to produce PWM signal by replacing those 2 timing resistors with a pot?
Yes, of course.
I figured, though I wonder, would it work from 0% to 100% and would it be linear?
+Power Max It would be reasonably linear, but there would be some non-linearities due to the diode behavior.
Sorry to bother you again but I have another question.
In the reset circuit, what is the function of the 6.8k resistor between the op-amp output and ground?
I breadboarded just this part and played around with the resistor.
The only thing I noticed was a slight level increase of the pulse when I disconnect the resistor.
Thank you in advance.
+Alwin Leerling Not really needed. I was playing with a couple of different op amps, and a few needed a pull down to completely shut off the transistors. With many rail-rail op amps, this resistor isn't needed anymore.
How can you predict that both Q1 and Q2 will turn on having the bases in parallel and a single resistor? Extremely well matched?
+Vale Sarbu Both transistors are turned on "hard", meaning both are going into saturation. No special matching needed in this case - just use the same type of transistor. Of course, you could simply use one more resistor to drive each base independently from the reset pulse generator.
Did you used to make synthesyzers?
Very cool!
Allan sir, where the heck do you get all these circuits or is it purely through experience
Some are my own, some are circuits I've seen elsewhere, or based on circuits seen elsewhere. Some are adaptations of circuits I've seen, or even circuits shared with me by friends.
Are you using tantalum or ceramic caps?? Thanks, having a go myself.
ceramic
Almost have it going. Only have one curve in XY mode. Stair step looks good though. Using LMC6492. Thanks.
I have a Heathkit IG-1275 Log/Lin Sweep Generator. I would like to display markers, say 10 marks both Log and Linear, across the X axis on an Oscilloscope using the scopes Z axis input to show the marks. Is this possible to display marks both linear and logarithmic across the X axis using the Sweep Gate Output, Sweep Output, or Analog Output of the IG-1275 using the Step Generator circuit #231?
+Gregory Burns You probably only need the 555 pulses. Reset the 555 at the start of the sweep, and then adjust the period of the 555 pulses to get the timing that you need. Of course, this will only work with the Linear sweep. For the log sweep - maybe multiple window comparators to detect the sweep voltage at various thresholds...
So if you make the 555 pulses wider, that means more time to increase the capacitor voltage so the steps would have a bigger voltage difference between?
Yes, exactly!
Hi nice video as always hopefully to view lesson about rgb analog ttl digital lvds signals and conversions. thanks
Hi,
After time domain, let's go to frequency domain..
So could you make a video about making a "frequency staistep" for a spectrum analyzer ?
Thank's !
May be Mr Carlson's could do this too.. Who will be the first to challenge this ?
So cool!!
The 0.1uF capacitor _is_ the memory. It's not a conventional 1-bit memory though. :)
Hi I like these kind of videos just wondring if i can give you a veroboard ver that i have done for this circuit
To help others that might want to make this.
I have had fun making this on veroboard over the weekend.
Thanks for reading
I have downloaded 99% of your videos and for this one I ran LTspice SImulation and got the same results. Would like to email you the Document I created for it but need an email address to send you the document for your review and also the simulation file?
Thank you for sharing your knowledge and making my day
+freqcy The best thing to do would be to post the files online somewhere (Google Drive, etc.), and then post the link here - that way, everyone can benefit from your work.
That right op amp is negative resistance circuit :)