Tue Nov 23 12:51:48 EST 2010
uC controlled analog circuits
The goal is to build something that can control an analog circuit
through a PIC uC. The path I'd like to take is some SVF filter with
variable feedback, using a digital resistor as the control signal D/A
It doesn't seem to be so simple to get OTA ICs these days to build
VCA, VCF circuits which have variable gain, so let's list some
- transconductance-based VCA (transistor or OTA)
- VCA circuits
- digital resistors
The problem is resolution. If the control envelopes are also
generated using analog circuitry that's not such a problem, but it
then does require a proper VCA.
Ok, let's try the digi pot. I have DS1807 and DS1801. Looks
like the DS1801 is more appropriate as I don't need the addressing.
It has a cool feature: zero crossing detection with a 50ms delay.
- Which PIC to use (18F1320)
- How fast does the 1801 switch?
- Use a filter IC or opamps?
- Max voltages on resistor terminals?
Switch frequency: the serial clock can go up to 10MHz (bit = 100ns),
there are 16 bits to transfer and the latch time is 200ns, so max rate
is 555kHz. That should be enough to do any kind of interpolation
PWM/SD modulation. The question with modulation is: how do glitches
behave? For use as input current feedback resistors
Using the PIC's HW shift register limits the debug interface.