PyGamer DACs limited to 2.5V - 2.6V ?
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PyGamer DACs limited to 2.5V - 2.6V ?

by kevinjwalters on Wed Jul 03, 2019 4:45 pm

The PyGamer DACs appear to be limited in their output to somewhere between 2.5V and 2.6V which occurs with a value of around 53000. Is this cap expected? I'm measuring this from GND/A0/A1 on the feather wing header connector on the back. Code from REPL session below, behaviour same on 4.0.1 and 4.1.0-beta.1, example shows just A0 but A1 and A0 + A1 together do this:

Code: Select all | TOGGLE FULL SIZE
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Adafruit CircuitPython 4.1.0-beta.1 on 2019-06-28; Adafruit PyGamer with samd51j19
>>> import board
>>> board.DISPLAY.brightness = 0.0
>>> import analogio
>>> aout0 = analogio.AnalogOut(board.A0)
>>> aout0.value = aout1.value = 0
>>> aout0.value = 0
>>> aout0.value = 32768
>>> aout0.value = 53000  ## about 2.5V
>>> aout0.value = 65535
>>> aout0.value = 0

I discussed this briefly on Discord and @danhalbert had a quick look at schematic and noticed A0/A1 are driving the headphones via some components which include 100+100 ohms to GND. I have nothing connected to 3.5mm socket. I do have the recommend small (mono) speaker attached to the amplified side of things via standard connector.

If this is a limit then are all the PyGamer audio functions coded to stay in the range 0-53000 or 12536-53000 (symmetric around 32768) for CircuitPython and MakeCode?

I tried same code on a Feather M4 running 4.1.0-beta.0 and that was ok reaching 3.27V at 65535.

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Please be positive and constructive with your questions and comments.