Feedback on circuit design

[Marc Nostromo [M-.-n]]

Thanks  a lot for the in-depth explanations.. it pretty much what I thought.




| 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 :)


| If your current voltage brings the CV negative, then you'll need to
| use the virtual ground (or bias point), however you need to be VERY
| careful.. you must *NOT* connect any ground on your circuit to the
| 'real' 0v of the monotron, you must ensure that your ground connects
| to the virtual ground (or bias) only.

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.

| Only thing I'd add is, don't expect miracles from your DCO, the
| MCP4822 is a fine DAC, but to use both channels takes a lot of CPU
| cycles, you need to write 16 bits to change a value on a single
| channel, if you're planning on "bit banging" the pins on the Teensy3
| this will eat a lot of CPU time. if the Teensy3 has a hardware SPI,
|it's a lot less of a load, but still slower.
| i.e. don't expect a 96Khz sample rate on your DAC ;)

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.

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

Thanks Paul !