[sdiy] dsPIC Stuff

[Scott Gravenhorst]

Oh my - the wall wart is not 10000 mA.  It's 1000 mA.  Sorry...  :)


music.maker at gte.net wrote:
>
>Robin Whittle <rw at firstpr.com.au> wrote:
>>Hi Scott,
>>
>>Thanks for these swinging, delicate little electronic music-box pieces!
>> I assume these are straight, without reverb.  The lower notes have a
>>somewhat resonant quality so it sounds rather physical.
>
>These are, in fact, completely bone dry.  Karplus-Strong is a digital waveguide model of
>a tight string.
>
>>Its great to hear what you have been able to do with three very small
>>and inexpensive pieces of *digital* silicon, DIP packages, protoboard,
>>hand-soldering and some serious firmware.  Did you write in C or Assembler?
>
>100% Assembly language for both the voice engines and the MIDI controller.
>
>>What do you think about the audio quality of the DACs?  
>
>Qualifier: I'm no audiophile - I think it sounds pretty good.
>
>>Did you go to any great trouble with power supplies, sheilding or op-amps to get the
>>desired audio quality?
>
>That's an interesting question - The power supplies - 9VAC 10000 mA wallwart powers the
>whole thing.  3 half wave rectifier power supplies with 3.3v 5A reg, 8v 1A reg and -8 1A
>reg.  Raw DC feeds to the regs: 3.3V has 3300uF, +8 has 470 uF and -8 has 470 uF.  No
>shielding at all, bypass caps are what is recommended by Microchip.  Very short wires. 
>Mixer/buffer opamp is a TL074.
>
>>Can you tell us the sample rate you chose?
>
>The DAC sample rate is 56.818 kHz.  The voice engines process the strings at 4 times
>oversampling.
>
>>For those not up to speed on the dsPICs with dual audio quality DACs,
>>they are in various packages, including 28 pin DIP:
>>
>>  http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=8192&mid=14
>>
>>This table used to list the dual channel 16 bit audio DAC as something
>>like "1-D/A 2x16-bit @ 100(ksps)", but I can't see this information now.
>> An example of the DIP devices with this DAC is the dsPIC33FJ128GP802:
>>
>>  http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en532298
>>
>>  - Robin
>
>Yeah, the part I used is the dsPIC33FJ128GP802, 28 pin DIP.  DAC is capable of up to 100
>ksps.  Maximum rate depends on how the DAC is clocked and if clocked from the system
>clock, what that clock speed is.  With 40 MIPS from a 20 MHz xtal using the system clock
>as the source, 89 kHz or so is possible.  I chose 56.818 because the math worked out to
>more in-tune strings tuned to concert pitch. The design emulates 
>a 50 string harp in range. 
>
>-- ScottG
>________________________________________________________________________
>-- Scott Gravenhorst
>-- FPGA MIDI Synth Info: jovianpyx.dyndns.org:8080/public/FPGA_synth/
>-- FatMan Mods Etc.: jovianpyx.dyndns.org:8080/public/fatman/
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>-- When the going gets tough, the tough use the command line.
>
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-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- FPGA MIDI Synth Info: jovianpyx.dyndns.org:8080/public/FPGA_synth/
-- FatMan Mods Etc.: jovianpyx.dyndns.org:8080/public/fatman/
-- Some Random Electronics Bits: jovianpyx.dyndns.org:8080/public/electronics/
-- When the going gets tough, the tough use the command line.