Analogue-sequencer

> will the daughterboard your doing change any of the 
> functuality of the 303 or is it just tapping in to the ins 
> and outs of the sequencer 
> This would be of intrest to me as i use the tb's sequencer on 
> other analog synths but it would be fun to use it on the odd 
> digital as well

The functionality is unchanged aside from the addition of midi.

The TB303 CPU has 9 output pins that send control signals to the synth
section.
There is a 6 bit note number, a DAC strobe that also activates the slide
circuit, an accent control and a gate control.
The 6 bit note number is written to a 4174 latch by a positive edge on the
strobe line. If the note is to be slid, this line stays high - which
activates the slide circuit.
At the same time as the latch is written, the accent line is clocked into a
D-type flip flop.
The gate line drives the envelope generators.

My daughterboard replaces the 4174 latch, giving it access to the note and
slide signals. It also intercepts the accent and gate signals, and takes
control of the slide circuit via 5 extra wires which solder in place of 3
resistors - there is no track cutting involved, and the board can be removed
invisibly.
Then when the 303 CPU 'writes' a note to the synth section, it is really
triggering an interrupt routine on the PIC, which captures the output from
the 303 CPU then passes it on exactly to the synth section within a few
microseconds. It also generates midi output data for the note.
If the PIC receives incoming midi data, it can write the note to the synth
section itself, independently of the 303 CPU.
Since this is all done at the digital signal level, the generation of the
note CV with the proper slide curve is identical to the standard 303.
To test it out, I captured a 303 pattern into my P3 (with the 303 synced to
the DIN output of the P3). I recorded it (at a low tempo so I could verify
note lengths etc) played by the 303 CPU, then by the P3 via the new midi
input.
I've put the original recording in one channel, and the P3 driven pattern in
the other:
http://www.colinfraser.com/misc/midibass303.mp3

I've used it so far to back up all my 303 patterns into a P3 dump. It's also
nice to be able to create patterns on the 303, then see what it was you
actually did ;-)

Cheers,
Colin f