Reading K-Type Thermocouple with nRF52840 on Coin Cell (2.3V to 3V)

[Luqman Naseer]

I’m using an nRF52840 powered by a coin cell (3V nominal, dropping to 2.3V) and need to read a K-type thermocouple. The challenge is finding an amplifier that:

1. Operates reliably from 2.3V to 3V.

2. Provides an output compatible with the nRF52840’s ADC range (0V to 2.8V).

3. Includes cold junction compensation (CJC).

4. Consumes minimal power.

Challenges

1. Most thermocouple amplifiers (e.g., MAX31855, AD8495) require ≥2.7V, which may not work at 2.3V.

2. Level shifting adds complexity and power consumption.

3. Integrating CJC while keeping the design simple and low-power.

1. Are there amplifiers that work down to 2.3V?

2. What’s the best way to implement CJC in a low-power design?

3. How can I ensure the output signal is within the nRF52840’s ADC range?

4. Any tips for minimizing power consumption?