K-Type thermocouple analog detect when 30+ degrees change

[Prasad]

I'm developing an application where i transmit K-Type thermocouple temperature to a mobile phone over BLE. For that i'm using ESP32 with MAX6675. And all works fine.

Now my problem is, this is a battery operated application and i need to put on sleep my main processor when the temperature is not rising (say below 70 degrees celsius, the device will be in deep sleep to preserve the battery power). When this device is functioning my heater element temperature goes up to 400 degrees celsius. I'm using ESP32 deep sleep feature and need to wakeup whenever temperature rises, say 30+ degrees celsius above from the room temperature. For that i can use ESP32 ULP coreprocessor to compare an analog input if there is a 30+ C temperature change. But unfortunately MAX6675 only provides digital output over SPI protocol. Which is not possible to read since the main processor is already in sleep and SPI protocol not supported on ULP coreprocessor.

What i'm looking for is somehow to interpret/amplify thermocouple input(Without MAX6675) to read an analog change of the temperature(No need to be precise at all, just to trigger the interrupt) to wakeup the main processor. Perhaps a possible circuit which uses simple set of components to amplify the thermocouple input?

For the op-amps i have only LM358 and i know it might not work as its low input offset voltage is 2mV.

Any suggestion/input are very welcome.

PS: Not to mention, i'm looking for an optimal power consumption.

[Deouss]

You most likely use wrong sleep mode. Maybe read more about it in documentation but basically some code must check your temperature periodically without waking up the whole system. I think it is possible to power up only small rtc domains during sleep.

[WiFive]

There is a built in LNA but it is not documented or supported in the driver yet. There is a ulp 1-wire driver you could use max31850.

Actually there is spi too https://github.com/espressif/esp-iot-so ... es/ulp_spi

[Prasad]

Thank you very much @WiFive i'll try this out and let you know the results.

[Prasad]

There is a built in LNA but it is not documented or supported in the driver yet. There is a ulp 1-wire driver you could use max31850.

Actually there is spi too https://github.com/espressif/esp-iot-so ... es/ulp_spi

Hi @WiFive, I've been working on ULP SPI example lately. Would you mind helping me out with this?

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