ADC change the attenuation level to 11dB

[overlander]

Hi,
I'm using wipy 2.0 with the expansionboard that measures the battery voltage on P16.I want to detect whether the wipy is powered from external powersource or if its running on battery.
When I read the value i always get 4095,the highest value from 12 bit range.So I tried to change the attenuation level to 11db that allows 3,3V input voltage to get a lower reading.
When I do:
apin = adc.channel(pin='P16',attn='ADC.ATTN_11DB')
an Type Error: Cant convert string to INT appears!
Has somebody sucessfull changed the attenuation level on the adc? Can please somebody tell me how this right.

[overlander]

@robert-hh
thank you for your quick reply.I see it-the quotes are wrong :(

[robert-hh]

@overlander The error message is quite clear, the way of telling maybe confusing:

from machine import ADC
adc = ADC()
apin = adc.channel(pin='P16',attn=ADC.ATTN_11DB)

See: https://docs.pycom.io/chapter/firmwareapi/pycom/machine/ADC.html