Pulling schematics from Nicolas Collins books Handmade Electronic Music and reading the helpful tutorial from Sebastian Tomczak's site, I decided I wanted to build a sequencer. The first sequencer I built was using the hex inverter 40106, binary counter 4051, and the multiplexer/demultiplexer 4040 chips. Essentially what the device is doing is taking the two initial oscillations from the hex inverter, one oscillator is controlling the timing of the sequencer, and the other is setting the initial tone to be sequenced. The hex inverter oscillates a frequency that is dependent on the resistor across the input/output and the capacitor to ground. By playing around with different values you can create different pitches (or timings). The 40106 hex inverter has six NOT gate. A NOT gate is logic circuit that reverses the signal being applied to it's input. So if a HIGH signal is sent to it's input a LOW signal is at it's output. If you connect it's output to it's input it will constantly shift HIGH/LOW/HIGH/LOW. The capacitor connected to ground it stores some signal for a period of time which in turn helps 'tune' the oscillations. Without the resistor the capacitor would not charge properly.
Once the oscillations are tuned to your desired frequency (or timing) the signal is sent to the 4040 binary counter. The frequency sets the timing of the counter in the chip and sends out a the first three signals to the address pins of multiplexer/demultiplexer. The different timings sent from the chip determine the which gate will be used on the 4051 (multi/demulti). As the counter cycles through the gates of resistance ladder. Different gates allow for different resistances. Those resistances on the resistance ladder go across the input/output of second oscillator, or the tone oscillator. Thus it creates a counter and multiplexor create a simple sequencer, based on the the oscillations of the hex inverter. Below is the schematic I used was from Sebastian Tomczak's site, and he probably explains what's going a little better. Plus there are some other schematics to try out.
SEQUENCER WITH AMPLITUDE EVNELOPE
The second sequencer was also based on Nicolas Collins book with help from Tomczak's page. It's a variation on the sequence above. The same basic principles are occuring, in that the oscillations from the inverter are defining the pitch and sequence tone, but now we added an amplitude envelope generator. So no only is the counter determining the sequence it is also sending signals to determine the amplitude of the frequency. Plus there is a volume and tempo adjustment. The schematic is below.
My first attempt at building the sequencer didn't go so well. I was getting some amplitude adjustments, but my initial frequency was really low and not really sequencing. I checked over the schematics and it seemed like I did things right, so I filmed it. Below is the the video.
I then realized that the capacitor for one of the oscillators wasn't connected to ground properly. Whoops. Since that oscillator controlled the sequencer that is why it didn't sound right. I attached the capacitor to ground, and then realized that I wanted I different initial note, so I changed it out. I also used a 50k linear potentiometer for the volume then the 100k logarithmic pot, cause it sounded nicer. Otherwise it's the same as before.