Let's Control It

Hi everyone,

before I start, let me tell you I love this project because of its simplicity to use.

Now I have been looking at building a BBQ thermometer with the ESP8266 since I got it, using MQTT to report. Options for temperature probes are a thermistor probe (using the ESP-Built-in ADC and doing some math using the Steinhart equation or use a table to look up the value) or a thermocouple probe using the MAX31855 I2C board or the 1-wire MAX31850 from adafruit (which will give me the tem directly without conversion, but special extended libraries from adafruit are needed).

Now my question before I elaborate: is there support in ESPEASY out of the box for any of these solutions ?

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Background:

Thermocouple or thermistor:

Thermistor:
popular BBQ thermometers seem to prefer thermistors like the ET-733 from Maverick. Measurement is done via a voltage divider, directly to the ADC with supposedly higher accuracy than thermocouples. As the change of resistance over temperature is not linear, they need some math to show the real temperature.

Thermocouple:
The more professional applications seem to use thermocouples like the ones from thermoworks( http://www.thermoworks.com), they are for more robust, have a wider temperature range, are more expensive but put out the real temperature directly. Also they need an ampifier board which does the magic to get the real temp values (e.g. https://learn.adafruit.com/adafruit-1-w ... k/overview). The amplifier boards exist in 2 different flavours, one as 1-wire, and the other as I2C. I2C does not allow for 2 boards withe the same address so if one wants 2 probes, a multiplexer circuit is needed or you need to use the 1-wire board (I think).

Use: I would ultimately want 2 probes, one for the air in the BBQ, and one for the meat. Both temps should be displayed locally by the oled display, and wirelessly sent to an MQTT server where an app on a mobile phone could have alarms etc. The accuracy in this use is probably not really needed, more the repeatability.

ESPEasy can only do some simple algorimic like single adding subtraction dividing or multiplication. So that will not be sufficient for a thermistor or thermocouple to get a accurate reading. The ADC in the ESP8266 is not highly accurate, voltage reference may vary from chip to chip between 1.05 and 1.1 Volt and on the low and the high end accuracy fails so the usable range is from .1 and 1.0 volt.

So the solution seems to be a I2C temperature probe , but it will be difficult to acquire a probe that can measure above 125 ℃. which you need to measure BBQ temperature.
Then the next best solution seems to use a interface board for a thermistor/thermocouple which will do the linearisation and has either a I2C output or a lineair voltage output. You suggested the MAX31855 but it is SPI bus and has no I2C bus.
Maybe a AD597 thermocouple interfaceboard will do the work for you.

costo wrote: Then the next best solution seems to use a interface board for a thermistor/thermocouple which will do the linearisation and has either a I2C output or a lineair voltage output. You suggested the MAX31855 but it is SPI bus and has no I2C bus.

You are absolutely rigth - its SPI. See https://www.adafruit.com/product/269
So the MAX31850K board from Adafruit remains: it has the 1-wire interface https://www.adafruit.com/products/1727

costo wrote: Maybe a AD597 thermocouple interfaceboard will do the work for you.

This seems to be a linearizing amplifier, so it has to use the ADC too.

For the MAX31850 you need a special plugin , for now that is not supported by ESPEasy.
If you use the AD597, this has a good linear response of 10mv/℃.
Power may be a single supply of 5 to 36 Volt.

Looking into the AD597 datasheet: Power supply needs to be 2 Volts higher than the max output, so with single Vcc of 5 Volt, maximum temperature can only be 300 ℃. Voltage output can be divided by 3 to stay within the ESP's ADC range. Accurate measurements can than be made between about 30 and 300 ℃.
If you need >300℃ temperature measurements you need a higher powersupply voltage for the AD597 and a greater division ratio for the ESP ADC.

Hi !

It´s an old thread, but I´ve added thermocouple support in the Playground:
https://github.com/ESP8266nu/ESPEasyPlu ... couple.ino

Dominik

Hi!

How do i add this to the 120 version?

Hi !

It´s an old thread, but I´ve added thermocouple support in the Playground:
https://github.com/ESP8266nu/ESPEasyPlu ... couple.ino

Dominik

Oyvindes wrote:Hi!

How do i add this to the 120 version?

Hi !

It´s an old thread, but I´ve added thermocouple support in the Playground:
https://github.com/ESP8266nu/ESPEasyPlu ... couple.ino

Dominik

hi there it seems the link is broken

regards

https://github.com/letscontrolit/ESPEas ... couple.ino

Nothing a little bit of phantasy and googling couldn't fix.

Hello,

i have a big Problem with my Thermocouples.
I added 5 max6675 Boards to the flashed NodeMCU. All Thermocouples show the same Temperature ( 26,5° ).
Any Idea whats wrong?

ESPeasy V 120
Max6675 Boards connected to GPIO-15, GPIO-16, GPIO-13, GPIO-10, GPIO-2

Im currently looking at doing the same thing as OP. I'm going to try 4x MAX31855 with 4x Type k probes from Auberins.com

Chamber x2 - http://www.auberins.com/index.php?main_ ... cts_id=327
Meat x2 - http://www.auberins.com/index.php?main_ ... cts_id=526

MAX31855 chips are from Aliexpress - I have one genuine Adafruit one, it seems to be an amplifier as well? No idea if the pure max31855 boards will be ok.

Has anyone gotten this type of setup working? I am actually wanting to use an ESP32 instead of my ESP8266-07 I have. Is there support for that chip yet?

Just posting to thread as I am going to be doing similar project. I have all parts needed, but have not yet got a chance to play so I will wait until I can post something worth while. Look forward to any update from other projects.