Feedback on circuit design

[Paul Maddox]

Marc,

> | nope, if you hook into where it says "cutoff" and goes into pin 6 of
> | IC4B (LM324) you'll be fine. You'll need an input resistor (10K like
> | the output of the LFO has) between your cutoff CV and that point.
>
> So that's R4 right ?
> What is the reason for that one exactly ? I got it 'working' but I'm
> still not sure why :)

Opamps are complex beasties, here's a good video that covers the
basics - http://www.youtube.com/watch?v=Q3RMFpGGcZM
basically each "input" needs a resistor, if you decrease the value of
the resistor that input has more affect on the output, increase the
resistor and it has less affect on the output :)

> In the very end, I would like to power the monotron directly from the
> teensy's GND & 5v. So I don't need to have battery for the monotron. I
> guess I'll deal with the negative CV. It's just a little more
> complicated to tune since the monotron pot's (including the pitch) are
> still enabled. I'll see where I got from there.

Well, you could "cheat" :)
The problem is the offset voltage, you could "add in" and "offset"
voltage, using another resistor and a variable resistor. This would
compensate for your output not being at the same level as the monotron
internals.
Or you could just make sure your software starts half way leaving you
11bits of DAC to play with rather than 12 (i.e. keep the MSB of that
output always high).

> As far as I know, the SPI is hardware. Also, I've been happy earlier
> with a full basic osc/filter inside the arduino that ran at 16Mhz. The
> teensy can be overclocked at 96Mhz so that should be all fine to do
> some nasty 8 bit set of oscillators. I've found some code to measure
> exactly the cpu cycles between two points in time. I'll use it to
> compute the cpu load and go from there.

96Mhz?
What chip is it?
SPI normally runs at upto 10Mhz, so watch that if you're planning to
overclock it.

> Exciting ! Next one will be the same setup except to control the
> mutable instruments filter board which should be even easier since it
> expects pwm as input and the circuit should end up being even simpler
> than this one.
>
> I'm going to grow my array of home made monosynths :D

Good for you :)

> Thanks Paul !

my pleasure,best of luck with it.

Paul