Nano based Drone Modulator

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Freedj
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Nano based Drone Modulator

Post by Freedj »

I have been working on a Nano based envelope generator for some supersaw drones. It started out being inspired by Ochd and the Hagiwo quad LFO and has evolved from there.

It has 4 CV Outs that range from 0 - 5v for the drone envelopes. The envelopes are all start out as ratios of each other (1, .6, .4, .25) and they drift a bit each time they change direction. The max drift adjustment is %5 of the base rate, with each cycle only drifting a little bit.

It has three knobs:
  • Overall cycle speed - This scales the entire speed of the module
  • Ceiling - This limits the max voltage of the output CV
  • Floor - This limits the lower voltage of the output to a percentage of the ceiling
I've always been frustrated trying to have a cycling slow envelope that stops when the master clock stops. This requires a clock to enable the envelopes, and once a clock is received the drones fade up and stay up until the clock stops, at which point they fade back out. Currently it waits 2.5s for the next tick before starting to fade out, and if it receives a tick while fading out it will just reverse and fade back in. I will probably make this auto-detect the clock rate and start fading out after 105% of the current clock rate in the future.

The circuit has been spliced together from various schematics to get it working, but I'll need to refine it more. Its using fast PWM through large caps to get a fairly smooth output.

The demo track is the three slower envelopes controlling vcas on supersaw voices. I wiggle all the knobs in the demo. The fade in / out is the clock start and stop.
IMG_2097.jpeg

kaputtpanzer
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Re: Nano based Drone Modulator

Post by kaputtpanzer »

Well I don't understand exactly what it does but it sounds damn awesome :banana:
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Freedj
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Re: Nano based Drone Modulator

Post by Freedj »

Here is a quick clip showing the envelopes and how they are effected by the knobs.

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soggybag
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Re: Nano based Drone Modulator

Post by soggybag »

Is that PCB with some jacks and ground connections on a header? I have to build something like that for testing prototypes.
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Freedj
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Re: Nano based Drone Modulator

Post by Freedj »

https://modularaddict.com/format/deskto ... cb-6pc-set

It sure is! They are opinionated, but great. It gives you +12 on one side and -12 on the other, but once you wrap your head around the relabeled bus bars it’s great! I’ve got two sets now.
kaputtpanzer
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Re: Nano based Drone Modulator

Post by kaputtpanzer »

Freedj wrote: Fri Sep 16, 2022 2:45 pm Here is a quick clip showing the envelopes and how they are effected by the knobs.

Now I get it. This is going to be a very cool envelope generator!
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Freedj
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Trigger input Schematics for Arduino

Post by Freedj »

IMG_2111.jpeg
I am starting to work on refining the schematic for this module, and I took a look at four open source modules schematics for how they implement trigger detection and protect the Arduino.

Hagiwo Gate / Burst Delay
This was my jumping off point because I have all the components to build this, and it was easy to put on the breadboard. I do not understand how this protects the arduino. The LED path is nice feedback but not necessary to the input.

Mutable Branches
Branches is the simplest of the MMBT3904 circuits. It is likely using the internal pullup resistor and when there is a input on the transistor base it gets pulled to ground.

Mutable Grids
Grids looks like it evolved from branches and it adds a 1M resistor from the base to ground as well as a external 10k pullup resistor.

Ornament & Crime
Finally O_c is somewhere between grids and branches, using the internal pullup resistor and changing the 1M resistor to a 33k.

Based on this small sample it seems that people designing for production are choosing the MMBT3904 route. What is the purpose of the 1M or 33k resistor in this design? If I wanted visual feedback could an LED be inserted between the MMBT3904 and ground? I am planning to use a Arduino Nano, which does have internal pull up resistors. Is there an advantage to having the external pull up like grids?

Would a 2N2222A be a reasonable MMBT3904 substitute for breadboard testing?
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Freedj
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Re: Nano based Drone Modulator

Post by Freedj »

I put a bit of time into front panel layout for this project and 3d printed various iterations.
IMG_2118.jpeg
Possible panel features:
* Peak (large knob) - Sets the max range
* Valley (small knob) - sets the min of the range
* Rate (small knob) - sets the primary cycle rate
* Chaos (tiny knob) - sets the amount of random
* Spread (tiny knob) - sets the distance between cycle rates
* Enable LED - shows if the module is outputing
* Output LED x 4 - shows the current level for each output
* Clock In - Enables the module on a clock
* CV In - Adjusts a parameter, configurable

In the beginning I think I was trying to put too many controls on the panel and expose parts of the code that I doubt i'll want to tweak once its finished. As you can see I gravitated towards 3 knobs, a clock input and a single CV. This will mean removing the spread and chaos controls from the panel but it makes it significantly simpler. Once I made that choice I started exploring how to make the panel feel more spacious. The last 3 versions are very similar in three panel widths.

V7 is probably too cramped to wiggle but I do like the size on the secondary knobs.
V5 Is probably my current favorite with the larger primary and limited feature set.

Which design would you prefer?
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Re: Trigger input Schematics for Arduino

Post by Synthiq »

Freedj wrote: Mon Sep 19, 2022 6:47 pm Based on this small sample it seems that people designing for production are choosing the MMBT3904 route. What is the purpose of the 1M or 33k resistor in this design? If I wanted visual feedback could an LED be inserted between the MMBT3904 and ground? I am planning to use a Arduino Nano, which does have internal pull up resistors. Is there an advantage to having the external pull up like grids?

Would a 2N2222A be a reasonable MMBT3904 substitute for breadboard testing?
The 1Mohm resistor pulls the base to ground when nothing is connected and may possibly give somewhat better noise immunity but I wouldn't go this route. The 33kohm resistor does the same but with better results due to the lower resistance. But it is also part of a voltage divider together with the 100kohm input resistor so the input voltage is divided by a factor 4 at the base. Since the base needs 0.6-0.7V to turn on, it means that the input has to be 4 times higher or 2.5-3.0V to trigger the input. It is generally a good idea to place the input threshold voltage in the middle between the low and high input voltage to maximize the noise immunity even if it probably isn't super critical here. Another advantage with dividing the input signal is that a -20V signal can be applied to the input without violating the -5V specified maximum base-emitter voltage so any regular modular voltage would be safe. How critical this is spec is I can't say, but transistors are used as noise sources when operating with breakdown in the base-emitter diode with no obvious ill effect so probably not.

The only reason to use external pull up resistor I can think of is if you want to use a different resistance value than the internal resistor.

If I LED on the input is desired, I would place it and the current limiting resistor between the collector and the positive supply and effectively in parallel with the pull up resistor.

The 2N2222 has lower current gain than the 2N3904 but will work as well (and so will most small signal npn transistors.) With lower gain the base current will be higher so there will be a larger drop across the 100kohm input resistor so the threshold will be slightly higher but can be adjusted by changing the 33kohm resistor to get the desired input threshold voltage.
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