Ramp pulse Op amp swap

[Kipper4]

https://www.circuitlab.com/circuit/m87u3v/simple-ramp_pulse-vco/

What do we think? Would a rc4558 do just as good of a job
Rich

[ElectricDruid]

Yes, I'd expect so. It's a pretty hacky circuit, so it won't matter much.

Slew rate on the Schmitt trigger might become a problem at the highest frequencies, but I doubt you'll care. If you did you'd be using something else

Tom

[Kipper4]

Driving it with a shmitt trigger integrator lm358 lfo.

im getting a sharkstooth wave on the ramp output 0.1v pp
and on the pulse output i have a triangle 0.25v pp

Not a fantastic voltage swing on the output.
I guess I can play with the biasing to try to get a bigger swing. Maybe upping the gain will work.
Why a bigger swing? 'cause i'm looking to drive a 555 vco and i'd like a bigger pitch variation.
It might be alright with a cd4046. I wouldnt kow, as I'm still waiting for the chips.
predicted delivery first week of december.


Have you another way, a less hacky way Tom.
I'd appreciate the input or suggestions to make it better or find an alternative.

I'm using a 1uf charge cap with the 4558.
green 5mm led with a 1k and 10k CLR (10k on the ramp)

[ElectricDruid]

It looks like what I thought it was doing and what it's actually doing aren't the same thing at all.

So then I tried simulating it (LTSpice). No dice, nothing happens. So then I tried following the links form the original schematic on Circuit Lab. It doesn't work in their simulation either and throws a lot of errors as far as I could see. "You need a valid circuit" and such like.

It's broken. Sorry.

What did you actually want? A CV-controlled LFO? with ramp and pulse outputs?

Tom

[ElectricDruid]

Here, try it:

https://www.circuitlab.com/editor/#?id=m87u3v

Go to the top bar and try "Time domain simulation".

[Kipper4]

Thanks Tom
I was looking for a way to get a ramp and pulse from an lfo.

Maybe I should look at something else.


I want to know how to create a pulse. A gate pulse? Not quite sure what that is.
Also trigger pulses.
Are they one of the same?
Not quite sure what I will be doing with it.
I just want to push and pull some lfos to find what works. How. It's limitations.

I got very interested when I saw a waveshaper at the weekend.
My brain will implode.

[ElectricDruid]

You should be able to find a ramp LFO easily enough. There are some designs that generate a ramp wave directly, and there are others that can be tweaked to do it, like the schmitt/integrator square/triangle design that we see a lot around here. If you put some diodes in it so it charges up faster one way than the other, you can get a ramp. You can even get a variable ramp-up/triangle/ramp-down if you want.

A "Gate pulse" is used for indicating that note is happening. On a keyboard instrument it goes high when the key is pressed, and it goes low when the key is released. It's a basic analog way of passing that information about what the player is doing to other parts of the circuit - envelope generators, typically. Notice that the *note you hear* might not match the Gate pulse - the envelope might have a "delay" stage first for example, or it could have a long Release stage that makes the note die away slowly after the key is released.

A Trigger pulse is similar but slightly different. They're just a short pulse of fixed duration, usually a few milliseconds. They have two main uses. One is for percussive sounds, where you don't care how long the key is played for, you just want..well, a trigger. Analog drum machines would use trigger pulses to play back their sounds.
The other use is as a second input on envelope generators, where they can be used to retrigger the envelope while the Gate is held down. This is important if you're playing a monophonic keyboard like a Sequential Pro-One or Minimoog and you want the envelope to restart for notes that are played legato. The trigger pulse can make this happen. However, not all envelopes have both Gate and Trigger inputs, and you'll sometimes see Trigger labelled as "Retrigger" since that is in fact what it does.

For waveshaping, I had a look at it recently for an article about sub-oscillators, but it all applies to normal oscillators or even LFOs:

https://electricdruid.net/a-study-of-sub-oscillators/

HTH,
Tom

[ElectricDruid]

You could try this one for a ramp LFO:

http://musicfromouterspace.com/analogsynth_new/OLDIESBUTGOODIES/LFO/lfo-2.html

You don't get a pulse output (well, you'd get a really narrow pulse output...) but you could add another comparator and then you'd get a pulse width control (or even pulse width modulation) for free.

HTH,
Tom

[Kipper4]

Thanks for taking the time to educate me Tom. It's appreciated.

I did try Rays Ramp lfo before but couldnt get it going on the breadboard. However It's working on the breadboard. So that's good news. I tried the comparator with a ua741 and scoped it. Wouldnt you know it. It works.
Within a certain range of voltages. I have a pot wired +9v>lug3   Gnd>10k>lug1   Wiper to inverting input.
ramp lfo signal to NI input. All driving and led>clr to gnd

The shape is not as clean as I expected. Maybe I should try a lm1458 or 4558 .
I only have one real comparator chip the lm311 and I'm not sure how to use it. I killed one last night with reverse power.

Anyone know how best to use the lm311 for this application.
So It will illuminate an led from the output.
data
https://www.soemtron.org/downloads/disposals/lm311n.pdf



cheers
Rich

[Kipper4]

Ooops revalation.
Tying the output to +9v with a 10k makes the led blink.
I'm in business.
Scope O'clock

[Kipper4]

What's on the breadboard and it's working as I want it too.

Is there a better way. What can I do to improve it?
Is the hysterisis R big enough? too big?
Should I change A3? Bigger? Smaller?

[anotherjim]

Depends on how much time the integrator amp spends >2v, it works until Q2 base-emitter junction fries?

SW2 is an on-off-on?

[ElectricDruid]

If the hysteresis works, I wouldn't worry about it. It's only improving the edges on your pulse wave, and I doubt you're much fussed about the difference between fast and faster.

Jim might have a point on the Q2/LED though. Add a base resistor, or hang it off OUT2 instead?

I also quite like the On-Off-On switch idea for a centre triangle wave, but the triangle will be roughly half the frequency of the other waveforms...

Tom

[Kipper4]

Thanks guys
I put the q2 to reflect what's on the bb.
I'll try to take note for next time.

I don't actually need it it's just there to show the Lfo works while breading.

Yes the switch can be centre off. I think the line 4ms does same.

So now I can do pwm in a hacky way.
Is this the only? Best? Worst?

What can be done to improve it? Anything?

[ElectricDruid]

No, there's nothing hacky about that PWM. You'll find a ton of classic synthesisers use a circuit much like that for their PWM waveform. In fact, most of them just use an op-amp instead of a proper comparator, so you've gone one better.

T.

[Kipper4]

So now I have a pwm signal.
What to do with it?

[Kipper4]

Nice little Trigger addition.
Plaguerised from the paia envelope follower
Did someone mention envelopes???

[Kipper4]

I guess I can use the pwm volts to light an vactrol and make a tremolo.  Enveloped pwm for variable stutter
?
Use the trigger pulse to do same and make a q and d sweller
?
Looking for inspiration

[ElectricDruid]

I dunno! I thought you were designing an LFO here, not an envelope-triggering circuit? Not that you can't trigger an envelope from an LFO if you want to...of course, you can.

Tremolo is one definite application of a PWM LFO waveform. Filter effects can also sound really good if you feed a second LFO to the PWM input. So you get a filter that jumps between high and low, but the amount of time it spends at each changes over time, without changing in frequency. Hypnotic, man...

T.

[Kipper4]

I dunno either matey.

You know when you think this waveform is what I need it's gonna be great and It turns all wrong.
Thank you for making me try the super simple ramp (Wilson) lfo again. I could never get it going in previous attemps.
I've learn so much.

Comparator (first time ever trying those chips.) Pleased to see I can light an led with it.
Thats got me curious.

Trigger pulses.  That too will light an led. Changing the cap might be fun too. Minimal testing so far.

PWM I know how to do it. as above. I have a better understanding of these pulses are now too.

You see after my recent dub siren thread I learnt about using a bjt as an Mute or in my case Unmute.
Curious again.
If this pwm signal will turn a bjt on/off so to speak I could let the signal go down to Gnd by turning said bjt on off and form a rudimentary tremolo. It might work. I'm prepared to give it some breadboard time. I might learn some more. Even if its what not to do.

I was wondering about a vibe too.

Dont even get me started on the enveloped pwm with blinky leds and LDR things.

I dunno! I thought you were designing an LFO here, not an envelope-triggering circuit? Not that you can't trigger an envelope from an LFO if you want to...of course, you can.

Tremolo is one definite application of a PWM LFO waveform. Filter effects can also sound really good if you feed a second LFO to the PWM input. So you get a filter that jumps between high and low, but the amount of time it spends at each changes over time, without changing in frequency. Hypnotic, man...

T.

What's that you say.
You mean just feed the raw tri output of a second lfo to the comparator.
I'm liking this already.

Buckle up this could be a bumpy ride.

I mean it.
Thanks for helping me learn.