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BMC003 - CV Arpeggiator PCB | Barton Musical Circuits

BMC003 - CV Arpeggiator PCB | Barton Musical Circuits


A very cool little circuit for turning single notes into arpeggios in your modular synth. It features controls for range, note sets, and movement. It contains a built in clock with outputs for triggers and gates, and can also be controlled by external clocks. There is an expander PCB that allows for external control voltage to be used on any of the stages and adds more control on the note set. It works on 15V and 12V supplies with no modifications, the PCBs have PC mounted pots for easy wiring and has footprints for Eurorack and MOTM power connectors.

This is for a PCB (including programmed microcontroller) only suitable for multiple formats.

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Availability:In stock

Note Generator Functions.

The note generator portion of the chip is controlled via 2 events and 3 parameters. These parameters and events control the output of the PIC's PWM which when filtered through a low-pass filter result in Arpeggiated control voltages The two events which control the note generator are:

  • Clock Events - control when the note generator changes notes. These come from the internal clock/divider or an external clock. 
  • Reset Events - Reset events control when the note generator goes back to the root note of the arpeggio. These can only be inputted from an external source

The three parameters which control the note generator are:

  • Range - limits the number of octaves the note generator can use. 
  • Movement - controls how the note generator moves through the note set; whether to generate the top or bottom note of a note set after a reset event and how to react when reaching the bottom or top. It is also has a "random" function.
  • Note set - refers to the musical notes contained in the arpeggio. Unlike the range and movement parameters, which are controlled exclusively by voltages, note set can be controlled either by an voltage exclusively or a voltage and a pair of digital inputs. A third digital input on pin 6 is used to change between methods of controlling note set. Wiring pads for the digital inputs are on the expansion board.

Internal Clock/Divider Functions.

To generate clock events for the note generator an internal clock or divider is used. When Pin 15 is held at +5V the internal clock is used, when held at 0V the internal divider is used. The internal clock has three hardware outputs and two parameters. The three hardware outputs are

  • Trigger - outputs a+5V pulse on pin 11 lasting roughly 5ms whenever the clock generates a new note event.
  • Gate - outputs a +5V pulse on pin 12 whenever the clock generates a new note event, the duration of the pulse is dependent on the gate PWM parameter or gate length parameter.
  • Indicator LED - outputs a +5V pulse on pin 10 in unison with the Gate output.

The two parameters are:

  • Tempo - controls the rate at which note events are generated. A voltage on pin 19 controls the tempo.
  • Gate PWM controls the pulse width of the gate/LED

The internal divider shares the same outputs as the internal clock, but the 2 parameters are replaced and an event is added. The new parameters are:

  • Division - determines how many external clock events it takes to cause a clock event
  • Gate Length - determines the actual amount of time a gate pulse lasts. It is not dependent on any other parameters


Additional Information
More Information
Brand Barton Musical Instruments
Additional Resources Build Guide

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