Inaccurate analog readings when ESP32 is connected to 3.3v on DUE

Other Hardware Sensors
1

Hi, I am reading a thermistor value at A0 which is a split signal from 5V to GND.
The arduino's 5V goes to resistor, then the signal is split into A0 and the thermistor which goes to GND.
This works fine and is very stable until I try to plug in an ESP32 to the 3.3v output on the Arduino to a separate GND pin from the thermistor's GND.

Is this due to a voltage dropoff, or something like a loss of amp?
Would a capacitor fix this issue, or do I need to plug my ESP32 to it's own dedicated power supply to get a stable analog reading?

2

Absolutely.

You need it to run the ESP32 at all.

3

Do you have 5v going to a DUE 3.3v pin?

4

The ESP32 runs fine with 3.3v off the Arduino's 3.3v. It's connected to the wifi and sending correct "internet" values over Serial2 to the Arduino.
Though that being said, the other analog components connected to the Arduino are being affected by the power draw to the ESP32 instead.

5

If you know better, go ahead.

6

No. I tried 5v from Due to 5v on 5v on ESP32, that wasn't enough for the wifi initialization on the ESP32.
Currently it's 3.3v pin on the DUE to 3.3v pin on the ESP32.

7

That's not what I asked. Good luck not frying your board.

8

I don't have any 5v going to any 3.3v line.

The 3.3v is only going from the DUE to the ESP32 and back to GND.
The 5v only goes to A0 and its own separate GND as I wrote in my post.

@Whandall Pardon me for interpreting "You need it to run the ESP32 at all" as a literal statement as if the ESP32 wouldn't work what so ever if it was powered from something like the DUE.

9

A0 is only 3.3v tolerant

10

@apf1979
I've only connected 5v to the analog pins on the DUE using the 680k resistor and 350k~ thermistor, which at least using the multimeter seems to drop 5v down to about 3.3v.
This should be fine for the analog pins on the DUE, no?

11

Theoretically yes.

12

The ESP32 will work only with a 3.3V source rated for the required current. The DUE is pretty unusual, in that it has the NX1117CE33Z regulator, which is rated for more than that.

So, "something like the DUE" would have to have such a regulator. The Arduino Uno, Mega, etc. do not.

The arduino's 5V goes to resistor, then the signal is split into A0 and the thermistor which goes to GND.

If you use the "arduino's 5V" as the ADC reference, then the voltage drop due to the large ESP32 current draw won't affect the ratiometric ADC readings.

13

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