Envelope generator with rise and fall control, sustain AR and no-sustain AD modes, rise and fall modulation.
Documentation: modules — Envelope
Product page: microrack — Envelope
Cv inputs for rise and fall with the ability to to loop the evolope 
question is how fast can this thing go?! 
Also something like this would be a great teaching point. I remember the first time i came across “end of cycle trigger” didn’t have a clue for months what that was typically used for as id been accustomed to having a switch or button simply labelled “loop”. Then i quickly realised damn this isn’t just a fun new flexible modulation sorce but its also a whole new sound source as well! I think its things like this people miss out on
We have issue with time range right now, but the range can be fixed by tuning of the resistor values. I plan to implement rise/fall time from about 30 second up to 0.005 second (200 Hz), so you can use this module as LFO and even as signal oscillator
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Hooray, big description update!
Wow, this is a flexible module!
At first I didn’t think much of it: one of those simplified envelopes, where you need two of them to build an ADSR. But often a two-stage envelope ist sufficient, and this analog gate input opens up so many more uses!
Versatility of the modules is what distinguishes a modular system from a sawed-apart monosynth. 
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I was inspired by Buchla envelope, Makenoise Function and another same ad/ar envelopes
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Good news: envelope generator is ready!
Rise and fall time changes from 40 s to 10 ms, so you can use this module as envelope, as LFO, as slew limiter and as envelope follower.
I really like the result and I can’t wait for you to appreciate it too.
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The output does a small “jump” at the start of each flank, which goes unnoticed in most applications, but is very obvious when used to modulate delay time (trying to build a flanger). It does not do that in sustain mode (but then it will not work as an LFO of course).
I have no idea what causes this effect, but then the envelope is one of the more complex circuits.
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I will investigate source of this jump. Maybe this is because of not perfect match between charge and discharge transistor circuits
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I have talked to a real electrical engineer (instead of just a hobbyist like me) about the circuit and we’ve come to several conclusions:
- output voltage follows exactly the voltage at C1, so any jump in output voltage must come from a sudden pulse of current into or out of C1
- the current into C1 comes from a current mirror controlled by RISE (or FALL) and R4 (or R5).
- actually the current mirror is controlled by the difference between EG_IN and RISE
- U3.2 makes sure that RISE follows along when EG_IN changes
- U3.2 has (like every OP-AMP) a limited output slew rate, so if EG_IN changes too fast, there may be a glitch that sends a short pulse of current into C1
- in Sustain mode EG_IN is generated by U1.2, another OP-AMP (with a limited slew rate), so U3.2 can follow along just fine
- in Attack-Decay mode EG_IN comes from the digital output of U2 (a NE555, i believe), which may change too fast for U3.2 to follow.
Of course this is all just theory and needs to be checked with the datasheets and, ultimately, with an oscilloscope. But maybe a capacitor from pin 1 of SW1 to ground (forming a lowpass together with R32) would mitigate the problem already.
Edit: I did some homework: the LM358-datasheet gives a maximum slew rate of 0.5V/µs, so a 12V jump would take 24µs. The NE555-datasheet says: rise time is 300ns, but that is a digital signal, so 300ns is the time between 10% and 90% of the new output level; no word about the remaining 20%. But it should be done in unter 2µs, which means that it takes U3.2 about 22µs to catch up, and during this time an uncontrolled current is injected into C1, making the voltage jump.
Moving SW1 to the input of U1.2 instead of the output would solve the problem, but I’ll still try the capacitor as a feasible fix for the already existing modules.
Edit again: here is the 'scope screenshot I should have provided at the beginning. Output of the envelope module in A/D mode at the top of the curve. The jump (ca. 0.4V) happens wthin 25µs, as expected more or less.
The first part of the jump looks almost linear, ca. 300mV in 12µs, which amounts to 25mA at C1, five times more than expected for normal operation.
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