ADC2 Channel cannot be used when WiFi is in use

[bestpika]

When WiFi.begin(...), I can't read all ADC2's channel.
All value is incorrect.

[prices]

I was just tracking this. I set up a simple circuit with a pot from VCC to GND with the wiper connected to IO34 and IO25. IO34 is ADC1, IO25 is ADC2. I used the following code in the Arduino IDE v1.8.1:

#include "WiFi.h"

unsigned long previousMillis;        // will store last temp was read
uint32_t delayMS;


void setup() {
  Serial.begin(115200);
  // put your setup code here, to run once:
    pinMode(34, ANALOG);
    pinMode(25, ANALOG);
    delayMS = 1000;
    previousMillis = 0;
    WiFi.begin("test", "testpassword");  // Comment this line out and it works.

}

void loop() {
  // put your main code here, to run repeatedly:
    unsigned long currentMillis = millis();
    if (currentMillis - previousMillis >= delayMS) {
        previousMillis = currentMillis;
        Serial.print("ADC1: ");
        Serial.println(analogRead(34));
        Serial.print("ADC2: ");
        Serial.println(analogRead(25));
    }
}

Results with WiFi.begin() in the code (binary size 507808 bytes):

ADC1: 608^M$
ADC2: 4095^M$
ADC1: 610^M$
ADC2: 4095^M$
ADC1: 608^M$
ADC2: 4095^M$
ADC1: 608^M$
ADC2: 4095^M$

Results with WiFi.begin() commented out (binary size 299472 bytes):

ADC1: 609^M$
ADC2: 893^M$
ADC1: 612^M$
ADC2: 894^M$
ADC1: 612^M$
ADC2: 892^M$
ADC1: 608^M$
ADC2: 896^M$

Before testing I completely wiped the flash on the device using

esptool.py --port /dev/ttyUSB0 erase_flash

Let me know if there is any more information you need.

[prices]

I found some information here:

#102

The comment is from igrr saying:
"This happens because ADC2 pins can not be used when WiFi is used."

I have yet to find confirmation of this in the data sheets, but I am still looking.

[prices]

Seems now I have confirmation that this is not a software bug. It is the chip itself. This will not get fixed in software.

[prices]

It seems that ADC2 is used with WiFi and maybe BlueTooth. That is why it is unavailable. So this might be fixed, but won't be fixed in this software. It will get fixed in the SDK.

https://www.esp32.com/viewtopic.php?t=1822#p10097

[copercini]

Let's concentrate ADC2 conflict with wifi here: #440
to keep the things organized =)

[prices]

I am just curious that you said we should concentrate the discussion in this bug, then closed this bug. Did you mean to point to a different bug?

[copercini]

Oh, I linked the wrong issue, this is the correct one (which I think is the same discussion): #102
Sorry =)

[danielcolchete]

For the record, resetting registers SENS_SAR_START_FORCE_REG and SENS_SAR_READ_CTRL2_REG to the old values they had before WiFi was turned seem to be a work around for this issue. And will allow you to use ADC2 again after you stop and deinitialize WiFI.

An algorithm here would be something like:
old1 <- SENS_SAR_START_FORCE_REG
old2 <- SENS_SAR_READ_CTRL2_REG
InitWifi
StartWifiAndConnect
(Do your wifi thing here)
StopWifiAndDisconnect
DeinitWifi
SENS_SAR_START_FORCE_REG <- old1
SENS_SAR_READ_CTRL2_REG <- old1

[danielcolchete]

I forgot to include the SENS_SAR_MEAS_START2_REG register. This one is important too.

[Hetric]

I forgot to include the SENS_SAR_MEAS_START2_REG register. This one is important too.

@danielcolchete, do you have the Arduino code to fix the ADC2 problem by any chance? I'm trying to use Bluetooth to send analog values from ADC2. I have no luck so far.