ADS1115 and PT100 - EL skills needed

[Lukeq]

Hello community

You may know BBQ. You also may know the company Weber. They build Grills for way to much money. So far, so well known.
I recently reverse engineered the Weber iGrill 3, which is in fact a pretty stupid Bluetooth thermometer with >>10m range for ~180€. So far, so well known.

Now, I want to create the same thing and improve. With ESPeasy, PT100 (they use 200k NTCs) and MQTT.
Therefore I added an ADS1115 with a sample PT100 (2wire for the beginning). I managed it, to measure the analog 3.3V thru henry's article.
Unfortunately I'm to stupid to calculate the Steinhart-Hart PT100 equation. Can someone help me with a correct T= formula please?

love, peace and ice cream

Lukas

PS: why can I add only 40chars in the formula input box?

[HomeJCL]

How do you wire the Pt100 ?

Do you have a 2 wire Temperature transmitter or is it a 2-wire Pt100 ?
With 2-wire TX it is fairly easy google 4-20mA on Arduino.

If you want to connect a Pt100 directly check this https://www.instructables.com/id/Readin ... g-Arduino/ haven’t read it but seems to address your question.

Although you can forego linearisation and extrapolate on the fairly linear behaviour and go for 0,385 Ohms/°C
Or you extrapolate a function in the most used curve part for your needs.

I use 2-wire TX.

[Lukeq]

PT100 directly, as I thought, the ADC can do the job.

In all samples I've seen, they use a voltage divider, which is as far as I know, not needed here. Or, can someone explain me, why I need this?
I have a reference voltage of the ADC and a resistor.