MIKADO
Analog Sequencing
System
Introduction
Mikado is a configurable
analog sequencing system, optimized for controlling a small (2-4
voice) analog modular synthesizer.
Mikado was designed to meet the need for a flexible, non-traditional hardware sequencer. A primary design goal was to include several modules for creating and manipulating rhythms using dividers, logic, and manual input. Flexible voltage sequencing, quantizing, signal routing, and manual inputs were other necessities.
Mikado is a "semi-modular" sequencer ala the Fenix or Serge systems, rather than discrete modules as other systems are. This is in keeping with the goal of controlling a small system, and reflects the designer's needs. Mikado could also serve as the heart of a larger sequencer system by adding modules from other manufacturers. In the present design, banana jacks are used for patching, though other types of jacks could be used by changing the front panel drilling accordingly.
Mikado's module complement and front panel were designed and specified by Jim Johnson. Electronic design and PC board layout are by Jim Patchell. PC boards for this project will be made available, and a customizable front panel is also available. It should be noted that, while the remaining material on this page describes the sequencer's specified configuration, the circuit and PC boards will have some additional capabilities, such as extra LED drivers, some additional sequencer modes, etc.
Modules
Mikado's module complement is as follows:
A mockup of the front panel is shown below.
Individual modules are described in detail in the next sections.
Master Clock
The Master Clock section provides clock signals to drive the rest
of the system. The clock source may be either an external MIDI
clock, or an internal voltage-controlled clock. In either case,
the master clock signal drives a gated divider network which
provides outputs for the rest of the system. The Master Clock
module therefore consists of three subsystems: the MIDI sync
generator, the VC clock, and the divider network.
MIDI sync
The MIDI sync generator derives a 24 PPQN signal from a MIDI
clock stream. It also recognizes MIDI Start and Stop signals, and
sets the Run line accordingly.
Internal clock
The internal clock is a voltage controlled square wave
oscillator, with a frequency range of roughly 8 to 80 Hz under
manual control. The clock rate is set by the Frequency knob. The
VC input provides 1v/octave control over the clock's frequency.
Source selection and gating
The Source switch selects a source for the clock and run signals.
If in the MIDI position, the Clock and Run signal come from the
MIDI sync generator. In the Internal position, the clock comes
from the internal clock, and the Run signal comes from the
Run/Stop switch, located at the lower left edge of the front
panel.
The Clock and Run signals are AND'd together to drive the divider chain. This ensures that these outputs start in sync with the master MIDI clock, if this is used; or it allows the user to use the Run/Stop switch to control the entire instrument, if the internal clock is used.
Run Output
The Run output is high when the clock is running.
Divider Chain
The divider chain provides divided outputs from the gated 24 PPQN
signal. The following outputs are provided:
The quarter note output has an accompanying LED. All divided outputs are set to the high state when the Run line goes high.
Sequencers
The system contains
two identical sequencers. Each sequencer has 8 stages, with two
rows (A and B); independent pulse outs for each step; individual
and multiplexed row outputs, and reset and direction inputs.
Clock and Up/Down
The sequencer advances from one stage to the next each time a
rising edge appears at the Clock input. The sequencer will
normally step forward (left to right); if the Up/Down input is
high, it will step backward. The sequencer will wrap from step 8
to step 1, or from 1 to 8 if the Up/Down input is high.
Reset
The sequencer will reset to stage 1 when the Reset input goes
high.
Rows
The two rows consist of 8 pots. The voltage range for each
pot is dependent on the setting of the sequencer’s Range
switch. Pots have linear scaling.
Pulse Outputs
The Pulse outputs go high when their corresponding stage is
active. The width of the pulse is dependent on the setting of the
sequencer's Pulse Mode switch.
Trigger Bus
The Trigger bus consists of eight SPST switches and an output
jack. The Trigger output produces a pulse for each step whose
corresponding switch is up (on). The pulse width is dependent on
the setting of the sequencer's Pulse Mode switch. An LED shows
the state of the trigger bus output.
A and B Outputs
The A and B jacks are CV outputs for the A and B rows.
AB Output
The AB output is connected to the A or B rows, depending on the
logic level at the A/B input. When this is high, the AB output is
connected to the B row; otherwise, it is connected to the A row.
LEDs beside the A and B outputs show the state of this output.
Range and Pulse Mode
Each sequencer has a Range switch, which sets its output range to
either 0 ~ 5 V, or 0 ~ 2.5 V.
Each sequencer also has a Pulse Mode switch, which determines the duty cycle of the Trigger and Pulse outputs. In the up position, these outputs will only stay high for the duration of the clock cycle; in the down position, they stay high for the full length of the step.
The range and pulse mode switches are located at the bottom of the front panel.
Pattern
Generator
The Pattern generator is a 16-stage trigger bus, and is similar
to the trigger busses on the sequencers.
When a rising edge appears at the Clock input, the pattern generator advances to the next stage. If the switch for that stage is in the On position (up), the pattern generator’s Out jack goes high for the duration of the clock pulse, and the accompanying LED turns on. The pattern generator resets to stage 1 when the Reset input goes high.
The Pulse Mode switch, at the right end of the switches, determines the duty cycle of the output. In the up position, the output will only stay high for the duration of the clock cycle; in the down position, it will remain high for the duration of the step.
Quantizers
The system contains 2 identical quantizers, which limit a voltage
to a set of predefined values. The values that can appear at the
output are determined by the Quantizer Scale switches.
CV In
This is the quantizer input. The input range is 0 to 5 volts.
Input voltages outside this range are clipped to this range.
CV Out
This is the quantized output.
Gate In
The Gate In jack has two functions. Quantization of the input
voltage occurs on a rising edge at the gate input. The gate input
also determines how long the Gate Output remains high.
Gate Out
This output goes high as soon as quantization is complete,
and stays high until the Gate In goes low.
Quantizer Scale Switches
These switches determine which notes will be produced by the
quantizers. Both quantizers are controlled by the same set of
switches, which are located at the bottom of the front panel.
Musical intervals listed below are assumed to be relative to 0 volts. Scaling is one volt per octave.
All/Some
In the All position, the quantizers output all semitones, and the
settings of the other three switches are ignored. In the Some
position, the remaining switches determine the quantizer outputs
Major/Minor
This determines the tonality of the output. In the Major
position, a major scale or chord is output; in the minor
position, a minor chord d or scale.
Scale/Chord
This switch restricts the output to the first, third, and fifth
notes of the major or minor scale in the Chord position. In the
Scale position, all notes in the scale will be output.
7th
This switch is only active when the Scale/Chord switch is in the
Chord position. When it is on, the seventh degree of the scale
will be output by the quantizers.
Transposer
The Transposer is used to add two voltages, and then offset the
summed voltages by plus or minus 1 volt.
In
These two jacks are unity-gain, non-inverting inputs.
Octave
This jack is an octave transpose input. If the voltage at
this input is above 0.25 V, the output will be transposed up an
octave; if less athan -0.25V, it will transpose down an octave.
Binary Divider
The binary divider provides /2, /4, /8, and /16 subharmonics
of the input signal. The divider outputs are triggered by a
rising edge at the Clock input. The Reset input forces all
outputs to a high state.
Prime Divider
The prime divider provides /2, /3, /5, and /7 subharmonics of
the input signal. The divider outputs are triggered by a rising
edge at the Clock input. The Reset input forces all outputs to a
high state.
Divide by N
The Divide by N module divides the input signal by a factor
determined by the setting of a rotary switch. The divisor 'N' can
be any value from 2 to 16. The / 2N and / 4N jacks provide the
specified subharmonics of the /N signal. As with the other
dividers, the divided output goes high in phase with the Clock
input, and is reset to a high state when the Reset input goes
high.
Sequential
Switch
The Sequential Switch
is a 4 to 1 analog multiplexer. The ABCD jack is connected to the
A, B, C, and D jacks in turn each time a rising edge appears at
the Clock input. When a rising edge appears at the Reset input,
the ABCD jack will be connected to A. Four LEDs display the
current state of the switch.
Analog
Switches
The Analog Switches connects one of a pair of jacks (A and B) to
another jack (AB). AB is connected to the A jack normally, or to
the B jack when the A/B jack is high. An LED displays the status
of each switch; it is on when the A jack is connected (that is,
when the A/B input is low).
One-shot
The One-shot is a
variable length pulse stretcher. The output goes high for a fixed
period each time a rising edge appears at the input. The period
is determined by the knob, and is variable from 2 ms to 5 sec,
with a logarithmic scale. The one-shot is retriggerable. An LED
shows the status of the output.
Flip-Flop
The flip-flop is a
simple D-type flip-flop. When a rising edge appears at the Clock
input, the logic value at the Data jack is passed through to the
Q jack, and to the Q (bar) jack in inverted form. An LED
indicates the state of the Q output.
Logic
The logic modules are
used to perform basic combinational logic operations on trigger
and gate signals.
Dual input AND/OR/XOR
The two dual input logic gates perform simultaneous AND, OR,
and XOR operations on a pair of inputs. The status of each output
is indicated by an LED.
Quad input AND/OR
The four-input logic gate performs simultaneous AND and OR
operations on the four inputs.
Inverters
The three inverters invert the logic signals that appear at their
inputs
1 / 0
These two jacks are wired to 5 volts and ground, respectively.
Toggle
Switches
The three toggle
switches are simple SPDT switches, each wired to a trio of jacks.
The jacks are located at the top of the panel, and the switches
are at the bottom.
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Logic
Switches
The four logic
switches output a logical 1 or 0. The jacks are located at the
top of the panel, and the switches are at the bottom.
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The first two switches are momentary pushbuttons. These output a gate signal that stays high as long as the button is pressed, as well as a trigger signal that goes high momentarily when the button is pressed. The trigger and gate outputs from the momentary switches are debounced. The second pair of switches are simple SPDT switches that connect the output jack to 0 or 5 volts.
Front
Panel
Mikado will use
a custom front panel produced by Schaeffer Apparatebau KG, a German machine shop. Schaeffer has a unique
advantage for DIY synth projects, in that they provide free Windows software for designing front panels. The output
from this program is emailed to their facility, and a drilled and
engraved front panel is sent back to the customer a few days
later.
The panel layout for Mikado is here, in Schaeffer format. (You'll also need to download this font file; just copy it to the same directory as the other .shx files that the Schaeffer program uses.) The front panel will require 8 units of 19" rack space. This layout is designed for Johnson banana jacks. If desired, the file can be easily modified for use with 1/8" or 1/4" jacks.
Most controls, especially those most likely to be manipulated during a performance, are placed at the bottom of the panel, out of the tangle of patchcords.
The banana jack colors follow the Serge scheme in general, with the addition of yellow and green for switch commons and poles, respectively.
The LED color code is as flows:
Logic levels
All trigger and gate inputs and outputs use positive logic,
where 0v = 0, and 5v = 1. The threshold for all logic inputs is
between 1.8 and 3.5 volts, depending on technology used.
Fanout
All logic outputs shall be capable of driving a minimum of 5
inputs.
Clock and Reset inputs
All Clock inputs shall advance the module to its next state on a
rising edge.
All Reset inputs shall reset the associated module to its initial state on a rising edge.
Input protection
All inputs shall be protected against overvoltages in the range
of -10 to 10 volts.
Divider Phase and Duty
Cycle
All divider outputs will go to a high state when the Reset line
goes high. Each divider output has a 50% duty cycle.
Schematics
Schematics for
Mikado are posted here,
on Jim Patchell's Web site.
Status
3/30/02:
Currently circuit design for Mikado is nearly complete.
4/04/02: Added Pulse mode switches.
4/16/02: The first of three PC boards
has been laid out. The final project will have four PC boards -
two are duplicates - all of which are the same size and are
designed for stacking.
4/21/02: PC layout is complete!
5/31/02: Fortunately, Jim P. has been
more active in actually building the sequencer than Jim J. has
been in keeping the web site up to date. The first prototype is
nearing completion: three of the four boards are stuffed, the
prototype front panel is complete, and parts are being mounted on
the front panel. The prototype should be done in mid-June.
8/2/02: Much has been accomplished in
the last two months! Most exciting, Jim P. showed off the
prototype at the Pacific Northwest Synth-DIY get-together in
Renton, WA on 7/20/02. Some modules were not yet working, but
enough good stuff was functional as to prove the validity of the
concept and design. Pictures of the prototype are available on Jim's web site. Since the
Synth-DIY meet, Jim has fixed most of the problems that cropped
up in the first boards and is getting ready to do a new set. In
the meantime, the quantizer is still being tested, and is getting
a change of scales. The front-panel layout has been tweaked some,
though that is not reflected in the file on this site nor in the
graphics above. Stay tuned!
10/7/02: Another seemingly long break with much
progress. Jim P. has finished the prototype which is now in Jim
J.'s hands. See below for a picture of the prototype in its new
temporary home. Jim J. will be evaluating and debugging the
prototype over the next few weeks. The front panel layout has
undergone some changes, and we're in the process of trying to
squeeze in a few more features.
11/9/02: Jim J. has recorded a short demo using Mikado to control a Fenix and SH-101 in realtime. proto.Type() is the name of the song.
Audio
proto.Type()
is a short piece that was created with the Mikado prototype,
along with a Roland SH-101, Fenix Modular, Electrix Mo-FX, a Zoom
reverb, and Mackie 1402 mixer; recorded in realtime to two
tracks, with minimal editing in Cool Edit.