hi @giuliomoro et al
so Ive noticed Ive got a slight high pitched noise coming thru...
(didnt notice previously, as i had a LP filter following it )
in the following plots,
the top one is belamini generating a 440hz sine connected to the scope. (powered via usb, or gpio i see the same)
the bottom, I disconnected belamini and instead generated the sine from the wavegenerator (so testing my circuit, in isolation to bela)
(Im using an analog discovery 2, so it can provide power/wave generator and scoping - nice device )
the noise looks similar, but you can see some repeating peaks, a ~3khz intervals,
which im guessing is what i can hear. even though it looks pretty quiet (-60db) in the plots, compare to the main signal ~0db), but given nothing else on FFT, its all I can think it is.
is this some kind of switching noise?
I disabled the LEDs, as mentioned in another but made no difference.
I was very tight on space on the protoboard, so left off capacitors to see if it 'would do', so half expected this
just wondering if there is a simple solution?
im wondering in particular is it some kind of noise coming from powering the op-amp from the same supply as bela?
Ive sometimes seen a capacitor put in between the supply (5v) to ground, would this help? what kind of value?
note: (for completeness, and in case its part of the issue)
i used 3.3k / 4.7kohm resistors for the opamp, to get the gain i need (1+3.3k/4.7k) as its what I had, that were close enough ... without using a series of resistors, which ... you guess it, i didnt have space for