LFOs

[theinmans at mindspring.com]

> I would actually be interested in buying such a midi synced lfo module
> if it came with source code.
> 
> fTom.
> (who some day will sync his vortex to midi clock which should be much easier)

This may be fairly straightforward.

1)  Get a MIDI to Sequencer Interface Chip from Blacet ($16
programmed).  
    This will read MIDI and give you a clock.

2)  a) Use a 555 Timer configured as an ADSR (see TomG's site for
examples). 
       Also see Barry Klein's book for examples of this chip used as
ADSR.
       Control the speed using a 4040 CMOS divider chip between the MIDI
to
       SEQ and 555.  A simple 1 to 12 rotary switch would work.  The
ADSR
       configuration would give you a great deal of control over the
shape 
       of your LFO.  OR
    b) Use the PWM idea Harry has been describing for voltage control.  
       Use the MIDI to SEQ chip to drive a one-shot 555 timer, using a
pot 
       to control the 555 pulse width of the "square" wave out.  Use
this 
       "square" wave trigger to drive any LFO circuit (one of the simple 
       transistor / relaxation circuits that provide a sawtooth; 
       a function generator or oscillator chip like the 8038(?) [see
current 
       Nuts and Volts] or 566 [see old Nuts and Volts for T. Henry's use
of 
       this as a voltage controlled oscillator]; or any of the many 741 
       circuits you could find in anything from a Delton Horn / Forrest
Mims 
       / Graf Circuit cookbooks.  For a couple of very nice voltage
controlled 
       LFO circuits, see Barry Klein's book.
    c) Skip the 555 timer for pulse width and go straight from the MIDI
to 
       SEQ to the LFO circuit through the two diode / one pot pulse
width 
       controller to trigger your LFO.  See Barry Klein's book for an
example 
       (p. 71 symmetry control). 

To the extent that this is a good idea, I am sure that it is either 
a) obvious or b) already described completely by another list member a 
year ago and I have just forgotten who.  :-)  [Probably all from Barry 
Klein's book].

Elliot (who is counting on better minds to correct me where I am wrong,
        lest I lead another astray)