Guitar input into Arduino-compatible ADC

[heuermh]

I have something working with the Arduino-compatible Teensy 3.1 and its built-in ADC and DAC pins.  The signal range on these pins is 0 to 1.2V and the docs say to avoid high source impedance.

https://www.pjrc.com/teensy/teensy31.html

There is also a separate audio board available that provides line in/out and mic input pins.

https://www.pjrc.com/store/teensy3_audio.html


I have a combo passive re-amp + SHO pedal that will handle line-level output signal back to unbalanced guitar level.  I am curious what people think about the different input options.

[heuermh]

Sorry, to complete my thought from yesterday, options such as

 - external active DI
 - adapt active DI circuit to 9V (or even 5V if possible) and include in enclosure
 - external passive transformer DI
 - external or internal preamp
 - built-in ADC vs. line-in on audio board vs. mic-in on audio board

[Ciaran Haslett]

Not sure if this answers your question.....but if it asks for a low z input then maybe a simple buffer is all that's required?  Thats the whole point of them after all.

And you could probably fit a 78l05 5V regulator somewhere to power the arduino whlie the regular 9V powers the buffer.

Didn't look too hard into this so sorry if it's way off base.

[heuermh]

Ah thank you, I may have been missing something in the terminology.  I didn't realize a buffer affected the impedance; looks like at least some of them do.  Might you know what the typical voltage swing would be coming out of a buffer?

[Ciaran Haslett]

Buffers are unity gain, meaning they do not amplify or attenuate their input signal.  Their job is to de-couple the guitar pickups load from the next circuits load, therefore retaining more frequency content from the pickups by reducing capacitance loss and therefore drive the guitar signal "cleaner" and "further."

But its the load change you're interested in.  And being that buffers don't amplify, the output voltage will be the same as the input voltage...whatever your pickups output.  Anything from 200mV to 3V peak to peak.

[heuermh]

Thank you.  Sorry if I'm being thick here.  :)

Turns out I have a unity gain buffer in my Paramix pedal, and I'd typically be using the Arduino pedal in the effect loop, so I'm good with impedance that way.

Then I suppose I'll want some way of attenuating the signal (100K pot?) and of boosting if necessary (a preamp/boost? what is the difference exactly?) before it hits the ADC or line in.

edit:  found this; has a built-in preamp (nice) and active mixer stage (which I don't need)
http://guitar-fx-layouts.42897.x6.nabble.com/Arduino-Guitar-Pedal-Verolayout-td7745.html