ADC accuracy

[dvarrel]

Hi,
I tried to work with adc value, but i can't reach accurate measurements.
what's wrong with my code ?

  import machine, esp32, time, os
  from machine import Pin, Timer, ADC, DAC
  
  led2 = Pin(2, Pin.OUT)    # create output pin on GPIO2
  adcPin = 36
  dacPin = 25
  adc = ADC(Pin(adcPin))        # create an ADC object acting on a pin
  adc.atten(ADC.ATTN_11DB) #max adc 2.6V
  dac = DAC(Pin(dacPin))
  Udac_max = 3.17 #max DAC voltage mesured
  N = int(1.0/Udac_max*255)
  dac.write(N)
  
  
  def timer(led):
      if led.value():
          led.value(0)# set pin to "off" (low) level
      else:
          led.value(1) # set pin to "on" (high) level
      print("read_uv():{:.2f}V".format(adc.read_uv()/1e6))
      N = adc.read_u16()
      print("readu16():{} U:{:.2f}V".format(N,(1.1/(2**16-1))*N))
      N = adc.read()
      print("read():{} U:{:.2f}V".format(N, (3.3/(2**12-1))*N))
      
          
  def start():
      print(os.uname())
      print(machine.freq()//10**6,"Mhz")
      print("hall sensor:",esp32.hall_sensor())     # read the internal hall sensor
      print("cpu:{:.1f}°C".format((esp32.raw_temperature()-32)*5/9)) # read the internal temperature of the MCU, in Fahrenheit
  
      t0 = Timer(0)
      t0.init(period=2000, mode=Timer.PERIODIC, callback=lambda x:timer(led2))
      
  if __name__=="__main__":
      start()

out:

read_uv():3.07V
readu16():61438 U:1.03V
read():3837 U:3.09V

[robert-hh]

A few comments:

• at an ATTEN value of 11 dB, the range is 0 to ~3.3V. The documentation is wrong, as can easy be calculated by 10**(ATTEN/20).
• In the printout for read_u16, you use 1.1V as reference instead of ~3.3. If you multiply the 1.03 by 3, you'll be at 3.09 then.

So I think the 3.07 or 3.09 readings are consistent. The DAC value you set has to be checked with a voltmeter.

[robert-hh]

Checking back at the espressif docs and my selection of boards, there is an interesting difference between boards:

• the old ESP32 have an initial range of 0-1.1V, and 0-3.3V at 11db attenuation, and a 12 bit resolution
• a ESP32S2 board has an base range of 0-0,85V, and 0-2.5V at 11db attenuation
• a ESP32C3 has a base range of 0-0,88 V

Interestingly, the espressif documentation makes no difference between mcu types, but an Arduino doc does, but even that one does not mention the older ESP32 models. https://docs.espressif.com/projects/arduino-esp32/en/latest/api/adc.html

[dvarrel]

Thank you, yes i measure 1.02v with my voltmeter at dac out Le 12 mars 2023 08:23:38 GMT+01:00, Robert Hammelrath ***@***.***> a écrit :

…

A few comments: - at an ATTEN value of 11 dB, the range is 0 to ~3.3V. The documentation is wrong, as can easy be calculated by 10**(ATTEN/20). - In the printout for read_u16, you use 1.1V as reference instead of ~3.3 So I think the 3.07 or 3.09 readings are consistent. The DAC value you set has to be checked with a voltmeter. -- Reply to this email directly or view it on GitHub: #11013 (comment) You are receiving this because you authored the thread. Message ID: ***@***.***>

[dvarrel]

Thé micropython doc said read_UV() returns directly voltage with calibration use of fuse Le 12 mars 2023 08:47:13 GMT+01:00, Robert Hammelrath ***@***.***> a écrit :

…

Checking back at the espressif docs and my selection of boards, there is an interesting difference: - the old ESP32 have an initial range of 0-1.1V, and 0-3.3V at 11db attenuation, and a 12 bit resolution - the new boards (Like S2) have an range of 0-0,85v, and 0-2.5V at 11db attenuation -- Reply to this email directly or view it on GitHub: #11013 (reply in thread) You are receiving this because you authored the thread. Message ID: ***@***.***>

[davefes]

The other note I have is:
'GPIO34-39 can only be set as input mode and do not have software pullup or pulldown functions.'
Seems to suggest that seeing as they have brought it out that you should be able to use that pin.
I see that it is a modified image, so unless they give you the details of the modifications then we are missing useful information.

Seems someone else had an issue with pin36
https://forum.micropython.org/viewtopic.php?f=18&t=4487&p=25968&hilit=pin36#p25968

[dvarrel]

on my other card, analog pin are shown like this : wemos d1 R32
can i MUX GPIO with micropython ? because ADC2 cause problems with WIFI

[davefes]

That is my understanding about ADC2.

can i MUX GPIO with micropython ?

Do you mean change between GPIO input and output? I hope so! I change from Pin to Pin hold and back again in some watering timers.

Or change from ADC to GPIO in or out?
I think you would have to deinit the ADC block
https://forum.micropython.org/viewtopic.php?f=18&t=10243
Good luck!

[dvarrel]

i mean IO_MUX changing
IO_MUX and GPIO Matrix (GPIO, IO_MUX)

[davefes]

Sorry, I haven't been down to that level on the ESP32.