These are chat archives for esp8266/Arduino

11th
Nov 2017
bobcroft
@bobcroft
Nov 11 2017 12:10
@brutzler Hi I think the probes are probably NTC thermistors. I work with gas boilers and values on thermistors used on boilers are commonly 15K at 70°C. An external I2C ADC would give you more scope since it would give you a wider input range of say 0-5 V whereas the internal ADC on the ESP8266 is only 0-1 V. You could either use a resistive divider or a capacitor charge / discharge circuit depending on your required range and accuracy requirement. I am sure a Google search will yield some helpful information.
Regarding calibrating your probe that is fairly easy if you have something like an existing digital thermometer to compare it to. Otherwise you need the data sheet to get the beta (B) value for the particular thermistor.
brutzler
@brutzler
Nov 11 2017 12:23
@bobcroft Yes, in the meanwhile I figured out, that it is a NTC 100K (also known as 104AT).
I am just struggling with the I2C-ADC. The considered part (ADS1115) can measure 2-5V (Why starting at 2V??). Even more than the ADC of the ESP. But if I would find one with 0-5V it would be a better resolution. Even if I supply the whole stuff only with 3,3V.
Resistance divider is what i thought of. Charge/discharge unit never used before. Will have a look on this too.
bobcroft
@bobcroft
Nov 11 2017 14:05
@brutzler 2 to 5 volt is the power supply range it can measure from 0 to 3.3 volt if 3.3 is what you power it with. Adafruit do a nice write up on their version of the ADS1115.
brutzler
@brutzler
Nov 11 2017 15:25
@bobcroft hey you are right. its measuring from 0 to VCC. There was some info, I missunderstood.
OK nw its easy. Some voltage divider, some calculating, comparing with a reference.... all done (hopefully)
thx!