Seq2 txt2

[tomg]

Or, What ever happened to tomg anyway?

This is a long one, which is appropriate because it took me a
long time.......

The Seq2 has been a reasonably good time. I could have stopped a
long time ago and wanted to but then we wouldn't have this Seq2
and that would be too bad. There were times I just wanted to stop
all together. "Damm it all, let 'em build the Seq1 or Henry's Super
seq just free me from this." It seems I can't do that. I have spent
the last 8 weeks thinking of nothing but the Seq2. Even while I did
the vcf2 stuff and on vacation I couldn't get it out of my head. I guess
the only real fix for me is to complete something. Just goes to show
you should never ever, give up on anything.

While I was doing this my focus became very narrow. I can already
feel the self-imposed weight lifting.

When we last saw the Seq2 things looked bleak for our hero. The
mean, evil, dastardly and all around bad guy CMOS gotchas' were 
whipping his butt. The real problem was me. I have this terrible habit
of getting a 5lb bag and then trying to put 10lbs of crap in it....

So the first thing was to lower my expectations a tad. Most of the
features I wanted are there. I lost a few goodies but gained a few in 
the bargain.

It works by making a clock from pair of 4001 inverters (any inverter 
will do). This clock can be a master clock for several sequencers 
so we need a panel jack to connect it to other units. Because any
sequencer may be a master or slave unit we also need a "clock in"
jack and a way to remove it from the circuit so a "clock on/off" is
also needed. The clock pulse can be entered manually by pressing
the "step" switch. 

While we are talking about the "step" switch lets talk about the 
actual momentary switches used. These need to have a very 
positive action to avoid multiple triggering. I like to use those 
large area calculator switches with a rubber foot glued to the 
switch surface. It works great and looks good too. Just avoid
those crap r/s momentary things. R/S did start getting them 
from a new supplier and they are better now...but just say no
and find something else.

The clock is sent off to the 4516 binary up/dn counter we are
using to drive the 4514 4-bit latch/decoder. Each incoming
clock advances the 4514 one output forming the basis of the
sequencer.

To give us a way to start and stop I used inverters to from a
logic switch that goes high on the first pulse then low on the
next. You can start the seq manually, use the "carry-out"
from another seq or any high going pulse. The output from 
this switch is used to control an or-gate made from another
pair or 4001 nor-gates. The switch holds one input high to
keep the output to the 4514s inhibit high. When the switch goes 
low the 4514s inhibit-pin is clocked at the same frequency as
the 4516 this causes the 4514s outputs to pulse with the master
clock frequency. Turning each output off before turning the next
output on.

These 16 outputs are sent to 2 16-diode pairs and 16 pots/leds.
The first set of diode are used to send pules to the gate the next
pulses to the slide/glide circuits. For fun these can also be used
to supply trigger outs. More on that later.

I didn't want to pulse the outputs thats why the last version used
two 4514s. Pulsing the outputs makes slide,gate and trigger for
each note available but puts a crimp in the idea of using it to 
generate bazaar waveforms it still works but not as well as it did.
I changed it because I was more interested in the sequencer
functions working correctly and it solves a few problems I ran
into.

The outputs are tapped to send every other output to a select
switch connected to a 4001 S/R flip-flop. The first note sets
the FF high advancing the 4017 repetition counter one. The notes
are fired in sequence until it reaches the "last note" set. This
resets the FF causing the 4017 to advance again this is the
first 4017 output that we use calling it one-repetition. Last note
also goes to an inverter/cap that resets the 4516 so we can 
count from 1 again. This continues until the 4017 reaches it's
last-rep when this happens the 4017 resets itself, the start-stop
switch and the 4516, stopping everything but the clock.

This way you can set the number or reps and the number of
notes played. There needs to be a infinite setting on the 
rep-counter but I keep forgetting to add one. It's just an open 
going nowhere so the 4017 never times out.

The last-note can also be used to reverse the sequence or
up/dn mode. Each time the FF changes state the u/d pin
of the 4516 is toggled. The circuit is always in u/d mode and
the 4514s outputs would reverse except that we are resetting
the 4516 everytime we get there. When the up/down switch
is toggled the 4516s reset pin is isolated from the last-note
position and the 4017s clock-in is disabled. This causes the
seq to run up/dn until the u/d switch is reset. Then the 4017
resumes it's count until it's done. 

Note that pressing the u/d button adds 1 to the count. So if
you want 4 reps with a u/d part you will need to set the rep-
counter to 5.

The pots are connected to each 4514 out and then summed
before going through a s&h circuit built from a pair of buffers
and a couple of 4066 analog switches.

The sample and hold section is controlled by the gate and
slide diode-selectors. There are twin pulse-width controllers
one for gate/note on-off and another for slide/trigger outs.
These may be set from a fast spike for each note to several
notes in length. So notes can be selected and slide to the
next note adjusted. At the last minute I added a 4013 DD 
FF and changed the slide circuit to accommodate glide functions.
This works by turning on glide at the first note set and leaving
it on until the next. Turning glide on/off as the sequence is
played. The 4013 is reset along with everything else so it
works the same for every repetition.

-tg