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I. Overview/Features

This module is a keyboard, only mounted with your other modules in your modular synthesizer 
rather than in a separate housing.  It does this by using a small number of push-buttosn instead of 
traditional keys.  This can be used like a traditional keyboard to play melodies, or it can be used a 
precision voltage reference for voltage controlled parameters in other modules.

CONTROLS

-Pitch select buttons.  There are 12 buttons corresponding to a chromatic scale.  They are arranged 
like a typical keyboard with sharp/flat notes in a seperate row.  Whenever two buttons are pressed at
the same time, the lower in pitch of the two will be output.  
-Octave select knob.  This knob selects which of five octaves the keyboard will output.  There are 4 
LEDs above the knob which give visual feedback for which octave is active.
-Slew knob.  This knob adjusts the rate of slew/glide/glissando between notes.  Fully 
counterclockwise is no slew at all.

OUTPUTS

-CV output.  This output goes from 0 to 5VDC in 1/12

th

 volt intervals to corresond to the 1v/octave 

standard commonly used in synthesizer modules.
-Trigger output.  This is a short pulse output whenever a pitch select button is pressed. It alternates 
between 0 and 5VDC
-Gate output.  This pulses up whenever a pitch select button is pressed and remains high (5V) until 
the button is depressed.

II. Schematic.

The schematic is on the next page.  I'll briefly describe the different parts of the circuit to 

help people understand the module.  At the top center is the 16F689 PIC microcontroller (the PCB 
has it labeled as a 16F685, this is a typo and should be ignored) which is the heart of the module.  

On the far left, we see the octave display LEDs.  Pin2 of the PIC is connected to the 

cathodes of the red LEDs and the anodes of the green LEDs, so this allows it to control which set of
LEDs are active, by either being a current sink for the reds or source for the greens.  Pin 13 controls
the anode of the first red LED and the cathode of the first green, and Pin 3 does this for the second 
set.  This allows us to control 4 LEDs with only 3 pins.

To the right of these, we see the switch matrix.  Pins 14 through 16 are the outputs. And pins

4-7 are the inputs.  When a single output pin is turned on, if any of the four switches that it is 
connected to through the diodes is closed, then the corresponding input pin will read this.  This 
allows us to get 12 switches from only 7 pins.

Below the switch matrix to the left are the two potentiometers.  Each is connected to +5V 

and ground on it's outer lugs and it's wiper is connected to a pin on the microcontroller.  The wipers 
are also filtered by a .01uf capacitor. Slew is connected to pin 19 and Octave is connected to pin 18.

To the right of the switch matrix we see the gate and trigger outputs.  Each of these consist 

of a section of the TL074 op-amp wired as a unity gain buffer, the output of which goes through a 
1K resistor to the corresponding output jack and a 1K current limiting resistor to an LED.  The 
trigger output comes from pin 10 and gate comes from pin 12.

Above these outputs we see the DAC and CV output circuitry.  The 4921 is a serial digital-

to-analog converter (DAC).  It receives data from the microcontroller on pins 2, 3 and 4 and then 
outputs a corresponding voltage on pin 8.  This voltage is then connected to a pair of inverting 
amplifiers in series.  The first has a trimpot in it's feedback path to fine-tune the output voltage.

Finally on the bottom we see the power supply connections.  There are eurorack and MOTM

power connecter footprints, these are connected to a low pass filter of a 10 ohm resistor and 10uf 
capacitor.  The power rails go to the TL074 and a 7805 voltage regulator.

Содержание BMC038

Страница 1: ...ated 11 16 2015 If you have any questions or need help trouble shooting please e mail Michael Bartonmusicalcircuits com I Overview Features II Schematic III Construction A Parts List B The Board C Calibration D Photos Final Thoughts ...

Страница 2: ...d LEDs and the anodes of the green LEDs so this allows it to control which set of LEDs are active by either being a current sink for the reds or source for the greens Pin 13 controls the anode of the first red LED and the cathode of the first green and Pin 3 does this for the second set This allows us to control 4 LEDs with only 3 pins To the right of these we see the switch matrix Pins 14 through...

Страница 3: ......

Страница 4: ...4W metal film through hole 8 2K 1 1 4W metal film through hole 10K 1 1 4W metal film through hole 100K 6 1 4W metal film through hole B100K Potentiometer 2 9mm Right angle PCB mount Like this 5K Cermet Potentiometer 1 3296W packaging Capacitors Name Value Quantity Notes 01uf 6 Cheap ceramic disc 10uf 2 2 5mm lead spacing 5mm width Other Name Value Quantity Notes Power connecter 1 Eurorack or MOTM ...

Страница 5: ...it to the panel This allows for more give to the parts making it easier to mount and also puts less stress on the PCB during the mounting process After everything is securely fastened resolder these connections then solder in the rest of the connections C Calibration 1 Set up a volt meter with the black lead to ground and the red lead to the CV output jack 2 Turn the octave knob so that only LED R...

Страница 6: ...t I just used the clipped off leads from the resistors this saves wire and saves time stripping wires I used bulk two row header clipped off instead of a shrouded header for my power connecter Here s a side view of the completed unit I did not use the washers that come with the pushbuttons if you decide to use them you may need to add washers for the pots as well ...

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