The Sentient Machine

[anotherjim]

Just tried part of the scheme above - only the top carrier oscillator. Here's what I found.
To make sure it can do it, I went for a higher 50kHz as a target.
Made as I drew it, I got poor asymmetry and distortion of the triangle. I could correct symmetry with a bias trimmer (100k pot) across the power supply feeding to 4069 pin 1 via a 1M resistor.
R1 needed trimming for max amplitude clean triangle. I had 390k.
With C1 at 100pF, I trimmed R7+R3 to 47k total.
Triangle good reaching about 90% of supply volts.
Any change in one value, changes frequency - including bias correction.

[Freppo]

Just tried part of the scheme above - only the top carrier oscillator. Here's what I found.
To make sure it can do it, I went for a higher 50kHz as a target.
Made as I drew it, I got poor asymmetry and distortion of the triangle. I could correct symmetry with a bias trimmer (100k pot) across the power supply feeding to 4069 pin 1 via a 1M resistor.
R1 needed trimming for max amplitude clean triangle. I had 390k.
With C1 at 100pF, I trimmed R7+R3 to 47k total.
Triangle good reaching about 90% of supply volts.
Any change in one value, changes frequency - including bias correction.

Thanks Jim!  You always come with great input
Sorry about that slow reply. Too many other projects in the works at the moment.

I've not had time to play around with that schematic yet, but I will follow your noted and and how it goes! First thing that hit me is that I could have set two comparators with reversed inputs (like in the schem you posten) insted of using an inverter. Would have saved two resistors. I'll do that for a later revision.

I have been trying another CMOS variation (without comparators) before and I've pretty good results results using this:


But it require more components and the schmitt trigger chip needs to be powered from a regulated 5v output (VB) to get a stable operation
It's also necessary for the trimmer, or it would have to be readjusted for any small voltage change (like a change of supply or battery voltage drop)

> triangle wave is very low amplitude.

The 5.1K:100K on top-right device sets the peak of the triangle to 5% of the supply.

Change that 100K to 10K. This will also drop the frequency a lot, you want a smaller timing cap.

And I believe the wave will become exponential instead of nearly-triangle.

But for supersonic triangle of excellent waveshape, both the plan and the chip seem funky to me. I would not spend a lot of time on it.

Thanks. I'm glad you stopped me from wasting any more time with that.
Although I see the potential for using this chip as a VCO. But that's something else entirely

[anotherjim]

I had the whole thing going yesterday with 2 comparators. Works but getting a very jittery pwm.
Slap my own head time - high resistance values make it very sensitive to noise on the breadboard AND stray capacitance is significant at higher frequencies. All meaning the schmitt trigger outputs have slow/unstable edges causing asymmetry & jitter. I now remember the last time I made those CMOS oscillators was for 5volt supply. Open collector comparators means the thing can easily run at 5v while the 4066 switches can stay with 9v. A regulated supply is a good idea anyway to keep things stable, in fact it became much better with only the voltage reduction. Next step is see if I can have it working with fixed resistors except for LFO rate & depth and no need for bias trimmers.

[pinkjimiphoton]

Hi folks,
I'm releasing a new DIY project today - The Sentient Machine.

It's a modulated resonant lowpass filter with two voices, a standard wah sound and a vowel sound.
At slow speeds it makes a cool phaser'ish sweeping sound.

It's based around a variable state filter with PWM/CMOS switches as variable resistors.
The vowel setting is made out of two filters tuned differently that are swept in the opposite direction.

More info, PCB, schematic (in the build doc) avaliable in my blog at www.parasitstudio.se

I hope you like it!

cheers
/ Fredrik

wow, fred, i'm sold!! pcb ordered!!
time to get my build on again i think. this is perfect for me... vowels, phasing, and that lovely phase shift tremolo!!

[anotherjim]

Well this is working -  as far as scoping the outputs. The resistance values can probably be scaled up for a pcb build. Schmitt triggers of both oscillators could be x10. R9 & 10 pull-ups maybe 47k - but I got obvious slewing of the outputs on the BB until reduced to 10k. As they are, rise time is about 400ns which is a lot faster than most op-amps would do.
Apart from current more than double, performance not much different with 9v for the 4069 and 339 versus 5v.
Note the added depth control. It doesn't go to zero, but Pulse width out wobbles close about 50% with depth resistor minimum.

[Freppo]

Well this is working -  as far as scoping the outputs. The resistance values can probably be scaled up for a pcb build. Schmitt triggers of both oscillators could be x10. R9 & 10 pull-ups maybe 47k - but I got obvious slewing of the outputs on the BB until reduced to 10k. As they are, rise time is about 400ns which is a lot faster than most op-amps would do.
Apart from current more than double, performance not much different with 9v for the 4069 and 339 versus 5v.
Note the added depth control. It doesn't go to zero, but Pulse width out wobbles close about 50% with depth resistor minimum.

I have finally had some time to play around with your schem Jim. Been too busy with other stuff...
It works perfectly! Great work. I might use this in a future design, if I have your permission?
By up scaling the resistors, you mean the two schmitt trigger resistors right?

wow, fred, i'm sold!! pcb ordered!!
time to get my build on again i think. this is perfect for me... vowels, phasing, and that lovely phase shift tremolo!!

Thank you for ordering! I hope that you will like it.
Please write a build report when/if you build it.

Cheers
/ Fredrik

[anotherjim]

Sure you can use it Frederik. Good to know it worked for you.
Yes, I mean the schmitt trigger R's that might be larger on pcb, especially the LFO - but to be honest, I'm not sure there would be much power saving in doing so.