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Project Notes

#505 Rakit Baby8 Sequencer

Building the Rakit Baby8, an 8 step sequencer with CV and Gate outputs and a clock input.

Build

Here’s a quick demo..

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Notes

The Rakit Baby8 sequencer kit is a simple 8 step sequencer with CV and Gate outputs and a clock input.

Each step has an associated CV potentiometer, LED and switch. The CV potentiometers can be adjusted to emit anywhere between 0-5 Volts from the CV out jack when the step is active.

The Baby8 belongs to a rich tradition of CD4017-based sequencers. The design goes back to the 70’s and most people quote a column called “Captain’s Analog” that introduced a simple 10-step design called the Baby10 (I haven’t been abled to discover where this column was published or the author’s name beyond it being be a guy called Mark).

Parts

Component Qty Checked & Installed
PCB 1
Stand-offs and nuts 4
500k Potentiometer 1
10k Potentiometers 9
10u Electrolytic Capacitor 2
4u7 Electrolytic Capacitor 1
100n Ceramic Capacitor 3
Blue LEDs 9
SPDT Switch - right-angle connector 1
SPDT Switch 8 √ (missing 1 in kit)
Mono Jack 3
1k0 Resistors 4
4k7 Resistors 2
10k Resistors 4
33k Resistors 2
47k Resistor 1
100k Resistors 3
200k Resistors 8
22k Resistors 2
CD4017 1
CD4093 1
LM324N 1
Battery Snap 1
1N4148 Diodes 9
78L05 5V Regulator 1

kit_parts kit_pcb_front kit_pcb_rear

Construction

Rakit have a very clear assembly guide online. Recommended build sequence:

  • switches
  • resistors (except for 4093 bodge)
  • diodes
  • capacitors
  • ICs
  • LEDs
  • battery clip
  • potentiometers
  • mono jacks
  • power switch
  • 4093 bodge resistor
  • stand-offs

After an hour or two - the finished kit…

kit_finished_front

kit_finished_rear

How It Works

The core of the sequencer is the CD4017 decade counter. This is nothing earth-shattering however - it simply uses the CD4017 as a designed as a decade counter. Each output has a potentiometer to set a specific output level, and diodes are used to steer the outputs to a common CV output.

The Baby8 embellishes the idea with:

  • a switch on each output that will either cause the sequence to reset at that output, or skip the output (depending on a master reset/skip selector switch)
  • optional external clock source
  • 5v regulated power from a 9V+ external supply

A CD4093 Quad 2-Input NAND Schmitt Trigger is used for:

  • a NAND oscillator to provide built-in clock source (with adjustable frequency and duty cycle)
  • buffer the clock for a few different uses: driving a clock LED; triggering the Gate output

An LM324 low-power quad operational amplifieris used for

  • clock duty cycle control (as a comparator)
  • output buffering and amplification

Test: Sequencing the Rakit Drum Synth

Some tips published on the Rakit blog: Baby You Can Bang My Drum: linking the baby8 & drum synth

  • CV Out ⇨ Pitch - the CV out for each step is set with the corresponding pot. Feeding this into the pitch input will change the pitch at each step.
  • Gate ⇨ Trigger - the gate triggers the drum synth at each step.

Here’s a quick demo of the Baby8 driving the Rakit Drum Synth..

clip

Credits and References

About LEAP#505 AudioMusicSequencer
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.