Monday, August 21, 2017

Modular Sequencing: 04 - And Gate Sequence

By combining short sequences with an and logic gate, complex and controlled rhythms can be created. Three interrelated patterns are created - the first sequence, the second sequence, and the points where both intersect against time and repetition.

With the assumption that both sequences are of different lengths, the resulting and logic will yield a rhythmic pattern that is longer than either. For example, take a rhythm that is eight steps long versus one that is only seven steps long. Fifty-six beats are required before the and logic rhythm will perform a perfect repetition.

A 40106-based oscillator is used to drive two 4022 counters. One counter has a loop length of the default eight counts. The other has a loop length of seven counts, which is achieved by connecting the Q7 output to the RES input. Selected Q output pins on the counters are connected via LEDs to the inputs of a 4081 and gate. The Q outputs that are selected form the rhythm of each loop. The selected outputs from the first counter are connected to the the first input of the 4081 gate. The selected outputs from the second counter are connected to the the second input of the 4081 gate. The resulting and logic will produce a rhythm formed from both counters. Three gate / trigger outputs are sent to the modular system - one output for the rhythm from the first counter, one output from the rhythm for the second counter, and the and logic rhythm.

Note that in this case, the LEDs are forming the rhythm, as there are no switches. By connecting the LEDs to different Q outputs on the counters, or by removing LEDs, the rhythm can be changed. By connecting the RES input to different Q outputs, rhythms of varying lengths from 2 - 7 beats can be achieved.

In this video example, the kick drum is from the first counter, the hi hat is from the second counter, and the tom is from the and logic.

Modular Sequencing: 03 - And Gate LFOs

LFOs with different frequencies can be used in conjunction with one or more logic gates to produce rhythmic patterns. These patterns are the result of the phase and frequency difference between the LFOs as well as the gate function, and can be used as a modular gate / trigger signal.

Two 40106-based LFO square wave oscillators are used to drive the two inputs of a 4081 quad, 2-input and gate. An and gate will only go high when all of the inputs are also high. The resulting signal from the 4081 and gate is then divided and output as a gate / trigger signal.

Each 40106 chip can be used to make up to 6 LFOs, and each 4081 contains 4 and gates. Multiple and gates can be connected in serial.

Similar functions that could be worthwhile exploring are or and xor gates.

Modular Sequencing: 02 - Eight Step Sequence

A rhythmic, eight step gate sequence can be a fruitful starting point for generating more complex patterns.

A 4022 octal counter is driven by a 40106 oscillator. Each counter increment is sequentially sent to one of eight outputs. A set of 8 on / off switches represents the rhythm, visually displayed in sequence using LEDs. The gate output is after the junction of the eight LEDs.

Note that LEDs with built-in current limiting resistors are used to make breadboarding easier. A rhythm loop of less than eight steps can be created by connecting one of the outputs Q1 to Q7 back to the RES pin, as opposed to connecting the RES pin to ground.

Modular Sequencing: 01 - LFO Gate

A simple LFO can be a useful source for generating a gate signal.

A 40106 hex inverter is used in conjunction with a capacitor and a potentiometer to generate a low frequency square wave. The voltage level is divided in half for a 6V gate signal. The output connection is then protected using a diode and a resistor. An LED displays the output signal.

The supply of the modular case is used as a power source for the circuit. Only the 12V and ground connections are used. 12V can be used directly with the 40106. A 10 pin socket to 10 pin socket modular power cable can be used to wire the power supply bus of the circuit.

The potentiometer and the capacitor can be replaced with different values to change the frequency of the square wave. One 40106 hex inverter can be used to make up to 6 LFOs.

The ratio of the lower 10k resistor compared to the upper 10k resistor determines the output voltage in relation to the supply voltage. If a different supply is used or if a different gate voltage is desired, adjust the voltgae division accordingly.

For example, if the supply voltage is 12V and a gate output of 9V is desired, the upper resistor could be changed to approximately 3k and the lower resistor to approximately 9k, yielding a division of 3k / (3k + 9k).

The two 10k resistors can be omitted if using a 5V supply.

Monday, August 14, 2017

64-Step Logic-Based Gate Sequencer

64-Step Gate Sequencer, created using a set of multiplexers, an inverter, a counter and an and gate. The LEDs and resistors could be replaced with switches.