"Baby8" CV Step Sequencer – Part 4 – In Use

By Kevin on September 1, 2024

These are the usage notes for my "Baby 8" style sequencer based on the ideas presented in "Baby8" CV Step Sequencer – Part 1 and using the PCB I've described in part 2 and part 3.

The video shows it connected up to my Educational DIY Synth Thing.

Warning! I strongly recommend using old or second hand equipment for your experiments. I am not responsible for any damage to expensive instruments!

If you are new to electronics, see the Getting Started pages.

Basic Single Use

The jumpers must be set as follows for single-use:

The key controls and principles of operation are as follows:

Tempo is set by the central potentiometer.
The number of steps is set using the rotary switch to between 1 and 8.
The pitch of each step is set by each of the 8 potentiometers to between 0V (off) and almost the power level of the supply (3V3 or 5V).
Each step can be skipped, but this only skips generating the GATE and TRIGGER signals. The CVs are still updated.
The TRIGGER signal has a pulse width that matches the current clock, so will be longer for slower tempos.
If all steps are active then the GATE signal will be on constantly.
CVs are constantly generated for all steps regardless of the use of TRIGGER or GATE.
The "run" switch can be used to pause the clock.

The following trace shows the interactions between the TRIGGER (yellow), reset signal (blue), clock (magenta) and GATE (darker blue) for a switch pattern where steps 2, 5, and 6 are being skipped.

Note that pattern has just started to repeat with the next step 1 and the skipped step 2 just on the screen.

Cascading Units - Untested!

There are two 8-way headers on the boards with pins as follows:

This means that it should be possible to plug the boards directly into each other, change the jumper settings and have the boards work in a cascade mode.

The final E_RST_OUT must be routed back to the first E_RST_IN. This can be done with a long jumper wire connecting the two "EXT" pins.

But there is also a "RTN" header pin which has no other purpose than to provide an internal return path back through each board, so one only has to jumper these two signals together at each end to make the return link, as shown below.

The "RST" jumper must be removed to enable cascade mode (note: this is labelled "INT RST" on V1 of the board, but "EXT RST INT" on V2).

Photo on the right shows the jumper set for external cascade operation. Photo on the left shows the jumper set for internal operation.

Cascading Clocks

When cascading the sequencers, all but one should have their clocks disabled. This means removing the "INT CLK" jumper. The board that retains its jumper will be the master clock for all the boards.

External Clocks

In principle it would be possible to disable the clock on all modules and have then driven by a completely external clock signal via the external IN CLK signal. Similarly in principle it would be possible to hook up the CLK signal of the external OUT header to another device.

Warning: This is not recommended as there is no protection circuitry for completely external signal inputs such as a clock or to drive completely external devices.

Use with the EduModSynthThing

A key reason for building this was to be able to use it with my Educational DIY Synth Thing. The following diagram shows how to do that for a module in single mode.

The key connections are:

GND and 3V3 to the Baby 8 GND/3V3 power input.
Baby 8 CV OUT to one of the VCO pitch inputs.
Then there are some options:
- Ignore TRIGGER and GATE on the Baby 8 and just connect 3V3 to the VCO CV.
- Connect TRIGGER and GATE on the Baby 8 to one of the EGs.
- Connect GATE on the Baby 8 to one of the EGs and then patch TRIGGER and GATE together.
- Connect TRIGGER on the Baby 8 to one of the EGs and then patch TRIGGER and GATE together.

TRIGGER will determine when the envelope generator starts (or restarts) the envelope. GATE determines when the release phase will start - i.e. when the GATE is released.

Just using the GATE as both gate and trigger means that a new sound will only be triggered after a skipped step. Just using the TRIGGER as both gate and trigger will mean that each note lasts half as long as the clock as each.

A key consideration is that the Baby 8 GATE will never be off if no steps are skipped, so the envelope will never start a release phase.

Another consideration is that if the release takes longer than each step, then subsequent steps, even if skipped, will still sound as the CVs are continually generated.

Closing Thoughts

It takes a bit of thinking about to realise how the GATE and TRIGGER signals interact with the envelope generator of the synth. But that is kind of the point - it is meant to allow simple experimentation to help understand what is going on.

In short, I'm really pleased with how this has come out.

Note: I'm waiting for V2 of the boards to return before I build several units to try the cascading, so whilst that is documented, at present it is untested.

Kevin