[Back to top]

Chrutil Modular MU Sequencer

This is a work-in-progress Arduino-based 32 note analog style sequencer compatible with Synthesizers.com modular synthesizers.

For questions and comments - please refer to this thread on Muffwiggler.

There is more stuff coming here in the weeks to come - please forgive the lack of details, I just wanted to get started describing the project, but I'll be posting all technical details about this eventually.

Here is a demo of the current state of the project (near complete):
"Third Demo - Part 1"
"Third Demo - Part 2"
"Third Demo - Part 3"

Here is an earlier demo of build in progress:
"Second Demo - Sorry for the very shaky camera here"

Here is the very first time I tried out the original prototype - humble beginnings
"First test"

Here is a picture of the full 8MU module mounted in the cabinet:

Here are the populated PCB's:

I attached the various PCB's to a plate that is then mounted on the pack of the panel.
I made the brackets using some flat metal that I bent with a hammered and an anvil and then drilled a few holes.
On the panel side it is attached by two of the pots.
The mount is much deeper than it could be - but I have plenty of space in my rack and wanted some space to work.

The schematics and PCB's were designed and fabricated with http://123d.circuits.io/
This is a very nice free web based collaborative schematics/pcb design tool, just sign up, grab my stuff, modify/improve them and order PCB's or download the gerber files.

Here is a description and link to schematics and pcb designs:

Reading 32 pots using four 4051 analog MUX: http://123d.circuits.io/circuits/38576-32analogreadermux
I haven't had any issues with this PCB other than it is very tight - or and the mounding holes are too small.
It is using three pin MTA-100 connectors to connect every pot using three wires.
They simply connect to the three pins on a potentiometer. (a cheap 100k alpha pot for example)
The middle row of connectors are very close together and you'll have to bend the cables in order to make it fit.
Before ordering a set of these I suggest making some adjustments to the PCB to make the MTA-100 connectors a little farther apart
If I were to remake this pcb I'd place the connectors are little differently and also change the mounting holes location and size.

Controlling 40 LED's with a Maxim 7219 LED Driver: http://123d.circuits.io/circuits/33885-max7219-breakout-board
Again, very tight fit with the MTA-100 connectors. I'd put each row another 100 mils apart if I'd to it again.
Also, you might look over the resistor value if you are tweaking the software and plan to have a lot of LED's lit at the same time for a long time.

Reading switches using six MCP23017: http://123d.circuits.io/circuits/52111-mcp23017-breakout
Each PCB breaks out three MCP23017 (you need two PCB's of this one) with individual address pins that you need to set jumpers for.
The layout is using three pin MTA-100 connectors again. The middle pin is ground and the outer pins connect to the top and bottom pins on an on-off-on three state switch.
For the four on-off switches I'm just using two pins.

MIDI I/O: http://123d.circuits.io/circuits/240363-new-midi-io
This is a simple MIDI in/out circuit.
This is wired to the serial port of the Arduino Mega - so once this is connected you can't upload programs to the Arduino anymore.
To simplify development there are two jumpers on the board that need to be installed for the circuit to work.
During development I hooked these up to a DPDT switch so that I can disable the MIDI serial I/O whenever I want to upload a program update to the Arduino.

Arduino Mega 2560 shield: http://123d.circuits.io/circuits/125147-arduino-mega-2560-sequencer-interface
This is the arduino shield that connects all the daughter boards to the arduino.

AD5668 16 bit 8 channel DAC board for Gate and CV outputs: http://123d.circuits.io/circuits/168953-dac-board-layout-2
DON'T FAB THIS PCB - It doesn't work. This is the DAC board that has the AD5668 DAC (SMD mounted on a Schmartboard) with CV follwer buffers.
Unforunately something is wrong here - and I'm not sure what yet. It should be a DAC and straight unity gain opamp CV followers, but the buffers don't work and regardless of what the DAC sends out, the buffers output 15V straight out so please don't use this board.
I will try to figure out what's wrong and update this soon.
For now I bypassed the buffers and have the DAC directly connected to the CV/Gate out which works well until I have fixed the problem.

Still to be done:
The output buffers on the DAC board does not work. Don't fab this board - it's a waste of money - the buffers will output 15V straight through regardless of the CV level sent by the DAC.
In my current prototype I am still using this baord, but I bypassed the buffers so I'm sending the DAC output straight out.
There are no input buffers or protection for the shift/reset analog inputs yet.
This is still to be done, but I need to understand op-amps a little better first.

Software:
The source code for the sequencer is currently designed to be used on an Arduino Mega 2560 with the Arduino IDE 1.0.5
The following third party Arduino libraries are used:
If you are interested - you can download the Arduino source code drop 1 (work in progress - some features missing, and things not terribly well tested)

The front panel is designed in AutoCAD with different layers for drill holes and screen print (or laser cut) graphics.

After etching the panel I taped the front to protect it during drilling (mandatory). I would highly recommend a drill press -
mine's a cheap one but it works well, in particular the laser aim works well once you calibrate it.
Also, don't forget to clamp the panel for every hole - the drill *can* bite, and the holes are more accurate if you do.
Drilling all those holes took a few days, but they turned out pretty well. There are something like 138 drilled holes of various diameters on this panel,
but you want to stay accurate so it is very important to take it easy and don't do it all in one sitting.
If you screw up drilling you might have to buy another panel and etch it - which could turn expensive.


Download the Front Panel AutoCAD DWG
Download the Front Panel PDF. This is a PDF generated from the DWG File. There are layers for drill holes and graphics as well.
Please validate the panel graphics before you spend money cutting/drilling/printing it - These are slightly different from the one I originally made so they are not validated.

Components Front Panel:
Note that there is nothing special about any of these, you can freely replace knobs, pots, jacks, etc. with different versions for a different look, feel and price. If you are cost sensitive you should price the full project before you start, this can get expensive and may not save you any money in the end - but cost aside you will have a blast building it!

Panel:
1 x 8 Unit Blank Panel Q134 from http://www.synthesizers.com
Pots:
34 x Alpha 100K Linear Potentiometer A-1958 from http://www.taydaelectronics.com
1 x Alpha Rotary Switch 2 Pole 5 Position
Switches:
40 x Mountain SPDT 3 Pin Flat 1055-TA2135B-EVX from https://www.mouser.com/
4 x Mountain SPST 2 Pin Flat 1055-TA2120B-EVX from https://www.mouser.com/
LEDs:
32 x Red 5mm LED's from http://www.taydaelectronics.com
1 x Red 5mm LED clear from http://www.taydaelectronics.com
LED Bezel:
33 x 5mm Chrome Metal LED Bezel from ebay
Knobs:
33 x 1" Cosmo knob from http://www.bridechamber.com/
1 x 1.1" Cosmo Chickenhead pointer knob from http://www.synthesizers.com
1 x 1.25" Cosmo knob (for the larger Tempo knob) from http://www.synthesizers.com (only available as part of the minimoog kit)
Jacks:
17 x Switchcraft RN112BPC Phone jack (because I got them super cheap). Easier with solderlugs version.
2 x Switchcraft 5 pin DIN MIDI female from https://www.mouser.com/
Pushbuttons:
2 x Switchcraft Red 502-903X from https://www.mouser.com/
1 x Switchcraft Black 502-913X from https://www.mouser.com/

Components back:
Wire:
#24 Pre-Bond tinned wire. Red/black/Grey/Whatever. About 300' of this. No kidding. from https://www.smallbearelec.com/
Wire Connectors:
MTA-100 2 Pin Lots of these
MTA-100 3 Pin Lots of these

Tools: Just for the curious, use what you have, but I liked having all these around.

Weller WESD51 Temperature controlled soldering station
Kester 331 and 245 solder
Craftsman hollow shaft hex drivers (doesn't scratch the panels at all)
Craftsman set of pliers, wire cutters, etc.
Rigol DS1102E Oscilloscope
Mastech HY3005F-3 Bench Power Supply
Vise-Grip wire stripper (saved my fingers)
Pana-Vise 350
AMP Handle 58074-1. Pistol grip MTA-100 connector crimp tool with 58246-1 terminating head. I started with the 59803-1 hand crimper, but after I drew blood three times in an evening I got the pistol grip.
Ryobi 10" Drill Press


I'm lucky to have access to this awesome place at work:
Epilog Laser Cutter/Etcher 120W Legend EXT
This is the laser etcher I used to etch the front panel. Contact me if you have access to one and want some advice on how to get the best results for etching anodized aluminum panels. It takes some tricks to get a good etching.

Suggested modifications:
LED Bezels. I sourced the chrome 5mm bezels from ebay, but would probably not use these again. They are difficult to mount without scratching the panel, and I actually prefer the look of the thin black plastic LED bezels used by Synthesizers.com. If I only knew where to source them..
Cosmo knobs. I got original Cosmo knobs from Scott @ bridechamber and Roger @ Sythesizers.com, but will probably use the knockoffs from https://www.smallbearelec.com/ in the future. They have both large and small knobs and chickenhead pointer knobs that looks great for a 25%-30% of the price of the real deal.

Electronics:
As stated above, the brain in this project is an Arduino Mega 2560.
There is no way to connect all the stuff on the font panel to the arduino directly so some circuitry is required to extent the inputs.
This is what I used:
4 x 4051 Analog Mux - For reading pots
6 x MCP23017 IO Expanders - For reading the switches
1 x Maxim 7219 LED driver - For driving the LED's
1 x AD5668 16 bit 8 channel DAC - this unit is surface mount, which is not my strength, so I also used a Schmartboard 0.65mm pitch 'soic to dip adapter' for easier mounting.
1 x 7812 Voltage Regulator

More to come here - schematics, etc.

As soon as I have gathered more details I will start a thread in the DIY section on the MuffWiggler forum, but until then feel free to send an email to me directly at: chrutil@hotmail.com
This account gets a lot of spam, so if you don't hear back in a few days, don't hesitate to resend!

Counter