Sampling Rate for ADC is extremely low

[pshanesmith]

As currently written, it appears you can only do about 93 SPS. It looks like if there is a shorter delay introduced on analog_read, it drastically increases the sampling rate and it seems to be running stable.

`
def analog_read(self, pin):
"""Read the value of an analog pin by number"""
buf = bytearray(2)
if pin not in self.pin_mapping.analog_pins:
raise ValueError("Invalid ADC pin")

    self.read(
        _ADC_BASE,
        _ADC_CHANNEL_OFFSET + self.pin_mapping.analog_pins.index(pin),
        buf,
        .0001,
    )
    ret = struct.unpack(">H", buf)[0]
    time.sleep(0.001)
    return ret

`

[caternuson]

That's probably there to enforce the underlying requirement of the seesaw firmware:
https://learn.adafruit.com/adafruit-seesaw-atsamd09-breakout/analog-to-digital-converter

Allow a delay of at least 1ms in between sequential ADC reads on different channels.

[pshanesmith]

Thanks Cater. In this case, the 1ms delay is being used between reads from the ADC on the same channel with no reads on other channels. I was able to update that number to a much shorter delay and it could run stable. I suppose there would need to be some detection for a channel swap I order to honor thale required delay while supporting faster reading on a single channel.

[todbot]

To address this somewhat, in PR #90 I allow you to specify the delay in seesaw.analog_read() that's then passed along to seesaw.read(). So if you know your application can support faster reads, you can tune down the delay at least.