ESP32 Forum

Posted: **Mon Feb 01, 2021 1:26 pm**

Hello,

I'm using an ESP32 Dev Module with Visual Studio Code, PlatformIO and Arduino framework.

I'm using all of the GPIOs from the the board in this configuration. 10 Anolog inputs to read a signal from external hallsensors.
And 10 Digital Output channels with PWM Signal on 200-400Hz.
And GPIO15 is used as 25KHz PWM Output for fan control.
GPIO15 is also connected to GND over a 10K resistor to prevent the ESP sending startup information.
The PWM Outputs are not connected to anything at the moment.

Code: Select all

//--------------------------------------------------------
// ADC Inputs
//--------------------------------------------------------
#define PIN_HALL_K0         36  //GPIO36 / ADC1 CH0
#define PIN_HALL_K1         39  //GPIO39 / ADC1 CH3
#define PIN_HALL_K2         34  //GPIO34 / ADC1 CH6
#define PIN_HALL_K3         35  //GPIO35 / ADC1 CH7
#define PIN_HALL_K4         32  //GPIO32 / ADC1 CH4
#define PIN_HALL_K5         33  //GPIO33 / ADC1 CH5
#define PIN_HALL_K6         25  //GPIO25 / ADC2 CH8
#define PIN_HALL_K7         26  //GPIO26 / ADC2 CH9
#define PIN_HALL_K8         27  //GPIO27 / ADC2 CH7
#define PIN_HALL_K9         14  //GPIO14 / ADC2 CH6

//---------------------------------------------------------
// PWM Outputs
//---------------------------------------------------------
#define PWM_K0              12  //GPIO12
#define PWM_K1              13  //GPIO13
#define PWM_K2              2   //GPIO2
#define PWM_K3              4   //GPIO4 / ADC2 CH0
#define PWM_K4              16  //GPIO16 / RX2
#define PWM_K5              17  //GPIO17 / TX2
#define PWM_K6              5   //GPIO5
#define PWM_K7              18  //GPIO18
#define PWM_K8              19  //GPIO19
#define PWM_K9              23  //GPIO23

#define FAN_PWM_OUT         15  //GPIO15

Also connected is a I2C LCD and an MCP23017 I2C portExtender, which are handled in Core0 to keep the cycletime of Core1 clean.

Now my problem is, everything is working fine, but the values which I get from the ADCs are not useable.

I connected all of the 10 analog inputs except GPIO25 and 26 to a 2V Voltage which generated with a 1M potentiometer out of the 3.3V pin.

Then I get this result:
564 656 683 695 701 705 0 0 714 711

Ok, this is a huge difference between 564 and 711, however, not calibrated.
But as soon as I connect GPIO25 or 26, everything gets messed up and I get something like this:

44 0 0 0 0 0 342 537 622 668

So as soon as I connect these pins to the same voltage, the values of the other inputs are messed up.
I'm monitoring the voltage on an oscilloscope and its constant at 2V.

So what's going on there?
Any ideas how I can get correct values on all 10 Channels?

I'm reading every 5ms at the moment.

I'm reading all 10 Inputs in a loop:

Code: Select all

ADCValue = analogRead( PinNr );

and I configured it once at startup:

Code: Select all

analogReadResolution(10);  //Set 10-bit resolution
analogSetAttenuation(ADC_11db);

What I'm doing wrong?

Posted: **Wed Feb 03, 2021 3:07 am**

Have you read this through.

https://docs.espressif.com/projects/esp ... s/adc.html

Posted: **Wed Feb 03, 2021 10:25 am**

username wrote: ↑
Wed Feb 03, 2021 3:07 am
Have you read this through.

https://docs.espressif.com/projects/esp ... s/adc.html

Yes sure, but this wasn't very helpful in this case.
Anyway, I solved the problem in between.
I replaced the 1MOhm Potentiometer with an external Power supply and then everythings works fine.
It seems like the ADC need some more current on the Input pins, which was too less with 1MOhm.
Is this specified anywhere?

ESP32 Forum

Behaviour when reading 10 ADC Channels

Behaviour when reading 10 ADC Channels

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