MicroPython Forum (Archive)

ADC.read_uv()¶

This method uses the known characteristics of the ADC and per-package eFuse values - set during manufacture - to return a calibrated input voltage (before attenuation) in microvolts. The returned value has only millivolt resolution (i.e., will always be a multiple of 1000 microvolts).

The calibration is only valid across the linear range of the ADC. In particular, an input tied to ground will read as a value above 0 microvolts. Within the linear range, however, more accurate and consistent results will be obtained than using read_u16() and scaling the result with a constant.

KJM wrote: ↑

Mon Feb 21, 2022 7:41 am

I've wound up the voltage at the analog inputs of several ESP32s set to ATTN_11DB over the years. I found the max 4095 count is reached at around 3.13v on my Fluke87.

liudr wrote: ↑

Mon Feb 21, 2022 4:00 am

So this ADC.read_uv(), it doesn't exist in 1.17 firmware. I tried 1.18. It's not there either. i wonder if this is just an issue with the document maybe copy-pasted from pyboard. The call class ADC(pin, *, atten) also doesn't work. It only takes 1 parameter. So under the current scenario, is there any way to read voltages more accurately? Thanks.

from machine import ADC, Pin
import os

print(os.uname())
a=ADC(Pin(33))
a.atten(ADC.ATTN_11DB)
print(a.read_uv()/1e6)

(sysname='esp32', nodename='esp32', release='1.18.0', version='v1.18 on 2022-02-22', machine='ESP32 module with ESP32')
0.142

scruss wrote: ↑

Tue Feb 22, 2022 4:59 am

liudr wrote: ↑

Mon Feb 21, 2022 4:00 am

So this ADC.read_uv(), it doesn't exist in 1.17 firmware. I tried 1.18. It's not there either. i wonder if this is just an issue with the document maybe copy-pasted from pyboard. The call class ADC(pin, *, atten) also doesn't work. It only takes 1 parameter. So under the current scenario, is there any way to read voltages more accurately? Thanks.

It came out after 1.18, so is in the nightlies:

Code: Select all

from machine import ADC, Pin
import os

print(os.uname())
a=ADC(Pin(33))
a.atten(ADC.ATTN_11DB)
print(a.read_uv()/1e6)

which gives:

Code: Select all

(sysname='esp32', nodename='esp32', release='1.18.0', version='v1.18 on 2022-02-22', machine='ESP32 module with ESP32')
0.142