[sdiy] Paralleling lots of ADC inputs

[Tom Wiltshire]

Thanks all.

Perhaps Brian is right, and I should just use a single ADC input at the master uP and then send the data via the comms link. After all, vibrato isn’t that fast, so it wouldn’t imply a super-fast sampling frequency. It seems like software might be a better answer than hardware for this one.

Thanks,
Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 30 Apr 2018, at 20:49, ASSI <Stromeko at nexgo.de> wrote:
> 
> On Monday, April 30, 2018 5:14:51 PM CEST Tom Wiltshire wrote:
>> So - I need to tie together several ADC inputs. Can I just tie them
>> together? Should I drive the tied-together-inputs with an op-amp follower
>> or something to make sure I’ve got a nice low impedance output? Or do the
>> inputs themselves need buffers in front of them (e.g. tied-together-signal
>> -> opamp buffer -> ADC input). Has anyone tried anything like this?
> 
> The datasheet should have some details what kind of signal conditioning the 
> particular ADC is expecting, but it's usually a bad idea to just tie together 
> multiple ADC inputs unless you can make sure they don't sample at the same 
> time.  Most ADC inputs present a time-dependent impedance that can be quite 
> low at the sampling point.  Also if capacitive sampling is used (very likely 
> these days), the paralleled input capacitances will influence each other and 
> degrade the ADC performance significantly.  At the minimum and only if your 
> actual source is already reasonably low-impedance I'd put an isolation network 
> in front of each input (RC lowpass is the most simple one).  An actual buffer 
> amplifier is better, but you might need an auto-zero buffer for your 
> application to get rid of offset voltages.
> 
> 
> Regards,
> Achim.
> -- 
> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
> 
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> 
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