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I need two constant differential voltage signals in the range of [-10V,10V] as input for two galvanometer-mirrors and so far I have seen several possibilities (e.g. with SPI-connected DAC-breakout boards or using the audio output with hardware modification as described here: Using Pi's built-in audio as general-purpose DAC?)

I finally found the HifiBerry DAC+: https://www.hifiberry.com/dacplus/

I'm not sure if can use this shield to generate constant output voltages which I then scale up for the full -10V:10V-Range.

Has someone did this already?

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From the picture shown on Hifiberry's site we learn that it uses the PCM5122 Audio Stereo DAC with PCM Interface and Fixed Audio Processing. We also find a RC low pass connected between "something" (traces coming from under the PCM5122 itself) and the audio out RCA connectors. R6, C8 and R3, C7 form these low passes. So the external circuitry does not block DC signals. This circuit might very well be the recommended output filter shown in the datasheet, p. 42 and where we find that:

The PCM512x devices include a two-channel DAC, with single-ended outputs. The full-scale output voltage is 2.1V rms with ground center output. A dc-coupled load is supported in addition to an ac-coupled load, if the load resistance conforms to the specification.

The same document also reads in the feature list (p. 1):

No DC-Blocking Capacitors Required

and

The PCM512x provides 2.1-V RMS ground-centered outputs, allowing designers to eliminate DC-blocking capacitors on the output, [...]

The datasheet furthermore outlines that the numerous integrated filters have a pass band of 0 to 0.4 (or 0.45) times sampling frequency with zero explicitly included and clearly shown in the frequency vs. amplitude plots.

Bottom line: while I am not sure why one would want to dc couple the audio signal and from theoretical knowledge only (not owning such a DAC+ board) it would seem that this board can in fact output a DC voltage of up to 2.1 V.


Maybe this is more fitting to your needs: Open ILDA DAC board?

  • Likely this is not used for DC coupling audio signals, but used as a digital-analog converter. – Thomas Weller Sep 19 '18 at 7:40

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