faster crystal?

  • I have the 40h kit.

    Would it be possible to swap out the cry16Mhz for something faster (without breaking anything)?

    Any potential side-effects?

    Does the firmware have any dependency on a particular speed?

    If the firmware needs to change, then that would defeat the exercise. I want to increase the clock in order to get around having to change the firmware. I'm finding the 16 bucket adc smoothing interferes with response in my application.

    So I figure the alternatives are to reduce the number of buckets or increase the clock speed.

    It would have been nice if kAdcFilterNumBuckets could be set at runtime using the monome serial protocol.

    thanks for any comments.

  • the crystal is maxed out, don't change it.

    you'll have to mod the code. it should be easy, but unfortunately requires a programmer.

  • oh well - tried not to go there...


    Will any jtag avr programmer do?

  • yes. i'd suggest the olimex. it's cheap.

  • Thanks for the prod.

    I ordered the olimex from Spark Fun:

    and installed the avr tools:

    The most difficult part of updating the firmware was getting my enclosure open again...

    The original adc smoothing/filtering was based on the averaging of 16 reads. Even with the 16 buckets I still had to do some filtering in my app. So I reduced the number of buckets in the firmware to 4 and increased the filter history in my app from the last 2 values received to 3. The firmware does smoothing (based on averaging the contents of the buckets) while my app does jitter filtering (based on hard compares to the last 3 values received).

    It's a night and day difference in response when doing fast full-off to full-on swings of the pedal (wah-wah style). Above a certain pedal speed, the 16 buckets meant that the extremes disappeared - the extremes were averaged away.

    in adc.h, changed:
    kAdcFilterNumBuckets from 16 to 4
    kAdcFilterRightShiftValue from 4 to 2

  • great to hear!

    i'm wondering how much could also be done on the circuit itself to reduce noise. a ferrite bead would help, on the incoming power line.

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  • okay...a cool thread too.