SEKU is a two-channel 16-step analog sequencer. Schematics of one channel are here.

Video-demo of SEKU controlling Korg MS10 and Roland S100M.

Heart of SEKU is CMOS 4520 dual synchronous divide-by-16 counter. RESET-in-jack must be normalised to ground when not used (16-step mode). Length of the sequence can be set to N by patching PULSE OUT from N+1 step to RESET IN jack. When no clock is connected to CLK IN sequencer can be manually stepped from STEP button.

CMOS 4067 1-of-16 analog switch is used for GATE, CV and PULSE outputs. Inhibit-pin of GATE OUT 4067-switch is clocked at the same frequency as the 4520 with 4001 nor-gate turning each GATE OUT off before turning the next GATE on. You can mute any one of the 1-16 steps with the STEP MUTE switch.

I have used slider potentiometers for STEP CV adjusting so that it is easier to draw waveforms when SEKU is used as an oscillator. I havent buffered the CV and GATE outputs with op amps in order to keep the power supply simple, just +5V to ground. I have also an adjustable power supply so I can adjust the octave range of SEKU by adjusting the supply voltage (+3 to +5 V or from 3 to 5 octaves in 1V/oct systems).