8000 ADC reading incorrectly when others are created in RP2 port · Issue #6833 · micropython/micropython · GitHub
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ADC reading incorrectly when others are created in RP2 port #6833

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benevpi opened this issue Feb 2, 2021 · 3 comments
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ADC reading incorrectly when others are created in RP2 port #6833

benevpi opened this issue Feb 2, 2021 · 3 comments
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port-rp2

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@benevpi
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benevpi commented Feb 2, 2021

In the below code, whether or not you created ADC3 affects the reading of ADC4. With the line commented out, I get a reading of about 17 degrees. With it there I get a reading of about 80.

import machine
import time

sensor_temp = machine.ADC(4)
blah = machine.ADC(3) # comment or uncomment this line to trigger / untrigger


conversion_factor = 3.3 / 65535

min_temp = 0
max_temp = 30

while True:
    reading = sensor_temp.read_u16() * conversion_factor
    temperature = 27 - (reading - 0.706)/0.001721
    print(temperature)
    time.sleep(0.5)
@benevpi benevpi mentioned this issue Feb 2, 2021
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@lurch
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lurch commented Feb 2, 2021

Just out of curiosity, I tried having a look at https://github.com/micropython/micropython/blob/master/ports/rp2/machine_adc.c but it seems to be using channel in confusing ways to refer to both the ADC channel and the GPIO number, so I couldn't really follow what it was doing 😕

dpgeorge added a commit to dpgeorge/micropython that referenced this issue Feb 3, 2021
@dpgeorge
rp2/machine_adc: Only initialise the ADC periph if not already running.
d4d82c7 
Otherwise it resets the ADC peripheral each time a new ADC object is
constructed, which can reset other state that has already been set up.

See issue micropython#6833.

Signed-off-by: Damien George <damien@micropython.org>
@dpgeorge dpgeorge mentioned this issue Feb 3, 2021
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@dpgeorge
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dpgeorge commented Feb 3, 2021

Thanks for the report, I can confirm the issue. It's because adc_init() is being called each time an ADC object is constructed, which turns off the temperature sensor switch.

Should be fixed by #6834.

@DWiskow DWiskow mentioned this issue Feb 3, 2021
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dpgeorge added a commit to dpgeorge/micropython that referenced this issue Feb 3, 2021
@dpgeorge
rp2/machine_adc: Only initialise the ADC periph if not already enabled.
7f7b4f2 
Otherwise it resets the ADC peripheral each time a new ADC object is
constructed, which can reset other state that has already been set up.

See issue micropython#6833.

Signed-off-by: Damien George <damien@micropython.org>
@dpgeorge
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dpgeorge commented Feb 4, 2021

Fixed by 7f7b4f2

@dpgeorge dpgeorge closed this as completed Feb 4, 2021
Wind-stormger pushed a commit to BPI-STEAM/micropython that referenced this issue Sep 8, 2022
@dhalbert
Merge pull request micropython#6833 from rshah713/main
e85cde0 
Fix typos and grammar in design_guide
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