Friday, June 29, 2007

Simple sequencer

Feeling all inspired-like from the gig last night, i made a cute little sequencer this morning. I like the fact that it is so very simple to make and so cheap, yet the whole thing can be extended significantly further. It uses digital logic with analog components and can be powered from 3V to 12V.

Yeah, the whole thing is very basic, and is really made up of three parts controlled by a single pot.

The 40106 provides an oscillator for control and an oscillator for sound output. The output of two of the inverters are fed back into the input of each stage, creating flip-flop type oscillators.

The 4040 creates multiple pulse streams of the control oscillator at binary divisions of its fundamental frequency. The Q1 pin outputs a pulse that is half the frequency of the input clock. Each consecutive Q pin outputs a frequency that is half that of the one before it. So, if Clock = 1, then:

Q1 = 1 / 2
Q2 = 1 / 4
Q3 = 1 / 8
Q4 = 1 / 16

and so on and on. There are a total of twelve output pins.

The 4051 provides a switching mechanism through which various points along a resistance ladder (the 22kΩ resistors) are selected to set the frequency of the oscillator for sound output. Three address pins (A, B and C) control which of the eight address connections are connected to the common pin.

The pot changes the fundamental frequency of the control oscillator. At higher frequencies, interesting effects seem to occur between the three ICs.

Audio Example
Simple Sequencer Example (MP3, 520kb)

Beware: the audio compression compromises the nice sound of wave! For true results, please construct one in physical form.

In the example, different sequences are achieved by connecting the address pins A,B and C of the 4051 to various outputs of the 4040. To be specific, four configurations are used as follows. It should be noted that the configuration in section 1 (A,B,C to Q1,Q2,Q3) has been represented by the logic diagrams and tables and the schematic and breadboard.
Section   Address Pin A       Pin B       Pin C
1 Q1 Q2 Q3
2 Q6 Q7 Q5
3 Q5 Q2 Q6
4 Q12 Q11 Q5
Here you can see the waveform of the oscillator.

1 x 4051 8 to 1 mux - demux
1 x 4040 12 stage binary counter
1 x 40106 hex inverter
8 x 22kΩ resistors
1 x 1MΩ potentiometer
1 x 0.1uF capacitor
1 x 33uF capacitor

So the total cost might be about $6.

Schematic and Breadboard


CK -_-_-_-_-_-_-_-_

Q1 --__--__--__--__ -> A (LSB)

Q2 ----____----____ -> B

Q3 --------________ -> C (MSB)

T: 1 2 3 4 5 6 7 8


T Q3 Q2 Q1 CD4051 Address
1 1 1 1 7
2 1 1 0 6
3 1 0 1 5
4 1 0 0 4
5 0 1 1 3
6 0 1 0 2
7 0 0 1 1
8 0 0 0 0


lucio.matema said...


I made a experiment with your schematic simple sequencer, very nice!!
I improve it with a CI386 and a pot to control the volume.



lucio.matema said...


Very nice experiment!

I made your schematic simple sequencer...
I improve it with a little amp - CI386 and 100uF capacitor...

thanks for the documentation,


Sebastian Tomczak said...

Thanks for your comment!

Anonymous said...

Cool article as for me. I'd like to read more about that matter. The only thing I would like to see here is a few pics of any gizmos.
Jeff Trider
Phone Blocker

Anonymous said...

So, if I understand this circuit well, you can add another 4051 (and another section of the 40106) and make a 16 step sequencer.

Or, add 3 4051s (and other 3 sections of the 40106) and make a 32 step sequencer!

It would be nice having a manual step button and a reset button.

Also, it would be an improvement to have a rotary switch to reset on step 1, 2, 4, 8, 16 and 32.

Obviously, each step (switchable on/off) drives a potentiometer (and a led) that will go to the CV out (to go inside the synthesizer's CV in).

That's what step sequencers are normally used for.