Power ESP32 with Vin pin while using ADC with a relative ground

Using Arduino Project Guidance
1

I have made a circuit for measuring temperature with a PT100 RTD and a ESP32 following this guide. I want to power all my project with a single supply (12 V - 1 A), so i have used this buffer amplifier as shown in the guide.

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For measuring temperature, i connected the output of the amplifier circuit to a pin and the "Virtual" ground to the ESP ground. In that way, if i connect the ESP by USB and power the amplifier circuit with my supply i can measure the right voltage.

Now i want to use only the supply, but i don't know how to use correctly the Vin pin for powering the ESP without affecting the ADC measure. I've tried to do a 12 to 5 volts converter but i am having several problems with the connections I've tried (converter ground to supply ground, converter ground to virtual ground, ESP ground connected to virtual AND supply ground).

Any ideas of how i can power the circuit with only the supply?

Thanks.

2

I just hook a 5V supply to Vin, works every time. What happens when you just use some 5V supply? Obviously the whole creating a power supply with a virtual ground is not working. And the ESP32 wants nothing to do with -6V.

Put the 12V into a 5V regulator and send that to the ESP32.

3

I'm already using a LM7805 as a 12 to 5 V regulator, but i have some problems. Where should i connect the regulator ground, virtual ground or supply ground? If i connect it to the supply ground, the output for the ESP32 measures -1 V, but if i connect to the virtual ground i measure ~4.7 V, but it's very unstable and drops to 2 or 3 volts and that's not enough for powering the board.

I think that last behavior is caused by the op amp used for creating the virtual ground, i suppose it can't stand the current of the others op amps and the ESP32, but i don't know what should i do to avoid it.

4

Stop with the op-amp already.

1 Like
5

stop with the virtual ground and the op amp already.

6

I've done this, but this affect my measurement

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7

It all began with an article in Destructables.
(Who'd have thought.)

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May you give me some help to make a circuit for using PT100 with an ESP32 and a 12V power supply?

9

Feeling Lucky??
Max31865 Spi Pt100/pt1000 Rtd-to-digital Converter Board Temperature Thermocouple Sensor Amplifier Module For Arduino 3.3v/5v - Integrated Circuits - AliExpress

Look for a MAX31865 library (that you feel you can understand) before you order that.

PE - PT100 range from 0 - 50C is like 100 - 120ohms.

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I don't think the author of that Destructables article understood that the results of his circuit not only depend on temperature but also on bridge supply and Arduino supply.
Get a digital PT100 chip, assuming you need one for the temp range you're measuring.
For room/body temps a DS18B20 is more suitable.
Leo..

1 Like
11

Adafruit has the Board ($15).
And a library.
Adafruit PT100 RTD Temperature Sensor Amplifier - MAX31865 : ID 3328 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits

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