Core 2 and ADC Input

bschwahn

Greetings everyone,

First I have really had a lot of fun exploring the Core 2 (my first M5Stack product)! A lot of features for under $50! My joy ended a little when I discovered the less then capable ADC functions which after doing a little research on the internet (and searching this forum) this seems to be related to the ESP32 processor.

With that said has anyone explored using a passive or active low-pass filter? My hope is that someone may have a schematic that someone would be willing to share?

The end-goal is to use a LM34 Temperature Sensor with the Core 2 as a thermostat for the radiant floor heating in my home.

Thanks ahead time if anyone can assist-Brian

PS: My first post to this forum :)

Arno

You can find some informations on the following posts.
For my part I abandoned the LM35 to use the DS18B20 and it works perfectly with UIFLOW

https://community.m5stack.com/topic/3782/waterproof-temperature-probe

https://community.m5stack.com/topic/3801/reading-analog-temperature-from-lm35-sensor/5

bschwahn

Howdy Arno and thanks for providing the links...I did take a peek at those already!

I'll take a look at the DS18B20 but I already purchased the LM34s (Fahrenheit version). I think the LM34 has a bit better accuracy yet DS18B20 is the less "painful" alternative!

I plan to:

look into the whole atten as that controls the voltage range to the ADC
look into an active low pass filter using a single supply Op-Amp
look into adding a small gain from the Op-Amp to get the voltage from the LM34 into an acceptable range for the ADC

Will share my findings along with any schematics I come up with.

Thanks-Brian

bschwahn

Hi all,

Some insights to share! Well the Active Low Pass filter did help to a small degree. With that said I decided to connect my Oscilloscope to the input of the ADC0 using GP35 and I was surprised by the amount of noise!

Input of ADC0 on GP35:
There was over 200mV of noise that varied in frequency of anywhere from 18 to 78MHz!

Measuring "ground" (just as a reference)
There was less then 100mV of noise that was around 60Hz which would be expected here in North America as our AC Line Frequency is 60Hz.

I did order some other one-wire temperature sensors including the DS18B20 and have another temperature sensor with a +_ 0.25 accuracy just to experiment with.

Again I will keep this post updated.

Thanks-Brian

ckuehnel

Please have a look to my blog https://ckblog2016.net/2018/03/03/esp32-adc-dac/. Sorry for German language.

david-bethesda

@bschwahn I would think a digital sensor would be much more accurate and easy to use than an analog one. Once you figure out what library you need for the protocol e.g. this might help https://randomnerdtutorials.com/esp32-multiple-ds18b20-temperature-sensors/