Update 'Future Modules'
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@ -4,28 +4,48 @@ What we build next?
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Pretty confident we do these in this order next.
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## Sequencer
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#### MK's 5-step sequencer, expanded to baby 8
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Something to generate CV, in particular for controlling VCO notes. The classic is called a "Baby 8", so called because it's a simple circuit that generates a sequence of 8 voltages controllable by individual knobs.
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#### MK's 5-step sequencer, expanded to 8 (or 10?)
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* Breadboard MK's 5-note sequencer.
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* Compare to online 8-note sequencers (baby 8)
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* Either build online 8-note schematic, or extend MK's 5-note to 8-note.
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* padding MK's out to 8 notes means roughly $16-20 in parts, depending on PCB choice
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* could also go to 10 steps, but no more (uses a decade counter)
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* expanding out to 8 notes means ~$16-20 in parts, depending on PCB choices
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* could also go to 10 steps, but limited by decade counter
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#### Bergman's 10-step sequencer (up to 10)
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* https://www.eddybergman.com/2022/04/8-step-sequencer-v2.html
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* can do up to 10 steps with the hardware to support it
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* 10-step mode is ~$16 in parts, depending on which are actually needed
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* big board, requiring one 8-pin, one 14-pin and one 16-pin IC
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* maybe more stable than MK's? test this
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* includes weird 8V linear regulator for the hex inverter - maybe save a bunch of effort and pins by using a single tl074, with two as needed and one as schmitt trigger?
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* very similar core to MK's, but using fewer diodes (substituting LEDs in many places)
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* might be more stable than MK's, but it's unclear what that means and whether it is true.
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* weird usage of a hex inverter, maybe for stability?
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* 10-step mode is ~$16-20 in parts, depending on which are actually needed
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* big board, requiring one 8-pin, one 14-pin and one 16-pin IC. But 3 panel-mounted UI elements for every step (plus some others), so plenty of room for a big board behind it.
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* includes weird 8V linear regulator for the hex inverter; if this can be replaced by an op amp in schmidt inverter mode, maybe both 7808 and hex inverter trigger are unnecessary?
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### Alternative: Midi -> CV
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We could generate CV some other way for now, such as:
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* build a keyboard using one of the two keybeds in storage; decipher key matrix, work out either MC or dumb resistor array to output correct volts for each key.
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* build a MIDI->CV module
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** [Hagiwo's cheap arduino version](https://www.youtube.com/watch?v=bHiZhLAntNI) and https://github.com/elkayem/midi2cv which it is based on
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** https://www.instructables.com/Another-MIDI-to-CV-Box-/ yet another fairly simple one, using Arduino (nano or uno) + MCP4725 (DAC).
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** https://hkadesign.org.uk/monotronkb.html for yet another version
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### Alternative: CV from something else
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* use a [raspberry pi running a DAW](https://old.reddit.com/r/synthdiy/comments/vbaj43/my_opensource_synthsamplersequencerdawinabox_the/) with a DAC and just use python to send CV; could also do midi-over-usb
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* buy a Korg SQ-1, which is what MK uses (and runs about $100 on ebay); Korg lists Trade-Up Music as a vendor?
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## VCF
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#### MK's Diode Ladder VCF
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* ~$8 in parts, two tl074 op amps and otherwise a bunch of diodes and support
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#### Kassutronic's KS-20
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* https://kassu2000.blogspot.com/2019/07/ks-20-filter.html
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** uses an LM13700 OTA (operational transconductance amplifier) (~$1.50, uncommon, and DIP marked obsolete) and NE5532 (uncommon, 80¢)
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* based on https://www.schmitzbits.de/ms20.html which is an attempted clone of a Korg MS-20.
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** that one uses a CA3080 OTA, an expensive and rare chip these days ($3/ea on amazon, maybe fakes)
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## VCA
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#### MK's VCA
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@ -58,7 +78,7 @@ Something to take CV in, round it to the nearest 1/12th of a volt (or whatever,
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* uses an arduino nano (other options probably fine), two 74HC595 shift registers (accidentally a pile in my collection) and the MCP4922 DAC (others may work).
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* Probably can build our own based on this and/or Hagiwo's quantizer, if going digital
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** https://www.quinie.nl/hagiwo-quantizer-how-does-it-work-a-bit-of-background/
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** https://note.com/solder_state/n/nde97a0516f03
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** https://note.com/solder_state/n/nde97a0516f03 and https://www.youtube.com/watch?v=op_DhPr2goc
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** arduino nano clone (atmega 328p), 12-bit dac (mcp4726) and small amounts of supporting hardware
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#### Microcontroller and smoothed PWM
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@ -134,6 +154,12 @@ Everybody needs several VCFs with different behaviors.
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** CA3080 High-Performance Operational Transconductance Amplifiers - not a jellybean, so $3/ea for sketchy NOS on amazon
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** CA3080 design is ancient; maybe an updated one exists with current ICs?
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#### Scrat
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* https://modularaddict.com/scrat-configurable-vcf-neutral-labs
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* plug in your own components to hear what they do
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* J175 jfet (~50¢) and H11F1M ($5!) optocoupler, otherwise basic jellybeans
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** can a cheaper optocoupler work? what's it even for?
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## CV Generators
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#### [Ornament & Crime](https://ornament-and-cri.me/) a highly recommenced "polymorphic CV generator"
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