[sdiy] CV/Gate delay project..

Didier Leplae didierleplae at yahoo.com
Sun Jan 31 03:06:59 CET 2021


Out of curiosity, if you were to use the PIC for this, would you also need a DAC? In my experience it seems most of the PICs have very low resolution DACs. I have found a couple that have 10bit but most are lower.

> On Jan 30, 2021, at 4:38 PM, Brian Willoughby <brianw at audiobanshee.com> wrote:
> 
> $1.44 Microchip MCP3221A 12-bit SAR
> $2.02 Microchip MCP3465R 16-bit delta-sigma (not recommended)
> $3.76 Cirrus Logic WM8196SCDS/V 16-bit 12Msps AFE
> $3.98 Texas Instruments ADS7054 14-bit 1Msps SAR
> 
> The last one is part of a family of pin-compatible chips that range from 8-bit to 14-bit, 1 Msps to 2.5 Msps, and some are differential (which you won't need for CV). Chips are available in a couple of packages, but they're not through-hole.
> 
> I'm getting the impression that through-hole is in low demand, and thus is high cost. Personally, I just pay an assembly shop to handle the surface mount, and I don't worry about it.
> 
> You can use a quality analog multiplexer in front to share one high-speed ADC across multiple CV inputs. Some ADC have this mux built in.
> 
> The key is to have the analog signals separated from the digital signals, so that the ADC does pick up the noise from the microprocessor.
> 
> Brian Willoughby
> 
> 
>> On Jan 29, 2021, at 13:04, Jean-Pierre Desrochers wrote:
>> You are right Tom..
>> I'm looking now for at least 14bits ADC.. 16 bits will probably be.
>> 12 bits DAC's should be fine.
>> Maxim MX7705EPE+ 16 bits ADC could do (I think).
>> 
>> As a note here:
>> I saw that synthesizers.com has a quantizer module Q171
>> that uses ADC/DAC process on incoming CV’s.
>> Here are the specs:
>> 
>> Specifications:
>> Panel Size: Single width 2.125"w x 8.75"h.
>> Quantization Method: Processor controlled ADC/DAC.
>> ADC Inputs: 10-bit with precision buffer/scaler.
>> DAC Outputs: 12-bit with precision buffer/scaler.
>> Gate Inputs: 0-5V minimum, rising edge.
>> Gate Outputs: 0-5V, 5ms on, 2ms minimum off.
>> Power: +15V at 30ma, -15V at 30ma, +5V at 50ma.
>> https://www.synthesizers.com/products/q171/q171data.pdf
>> 
>> The CV inputs are fed to precision opamps OPA4277
>> then routed to a micro MEGA644P’s  internal 10 bits ADC.
>> The CV outputs are from 12bits DAC’s LTC1448.
>> 
>> So… I’ve not tried this module but assumes it works correctly
>> using a micro’s internal 10bits ADC and an external 12bits DAC.. ??
>> 
>> Hmmm.
>> 
> 
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