Operate a Sensor with ADC over NFC using ST25DV64KC without Microcontroller?

[MERSI]

Hi everyone,

I'm working on a low-cost, batteryless NFC-based sensor node and would appreciate your input.

My goal is to measure an analog signal using a basic op-amp + ADC circuit (e.g., voltage, temperature), digitize the signal via I²C-compatible ADC, and store or transmit the data using an ST25DV64KC dynamic NFC tag. The NFC reader (e.g., smartphone) should power the system via the tag’s energy harvesting output (V_EH) and read the data wirelessly.

To minimize cost and complexity, I would like to avoid using a microcontroller. So the intended setup would include:

• analog frontend (op-amp),

• I²C-based ADC,

• ST25DV64KC.

In addition, I would like the same system to read a second passive NFC tag, such as an ST25TV02KC, to get its UID or basic data.

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My key questions:

1. Is it feasible to build this system without a microcontroller, using only ADC + ST25DV64KC?

2. Since both ST25DV and most ADCs are I²C slaves, is there any way to operate them without an I²C master?

3. Would a microcontroller still be required to control the ADC and handle the ST25DV interface?

4. Is the harvested power from the NFC field (V_EH) sufficient to run such a setup for short bursts?

5. Is it possible for the system to read another NFC tag (like ST25TV02KC)? If yes, how?

6. Are there microcontrollers with integrated NFC reader capabilities (ISO15693)?

7. If not, what would be a recommended minimal and cost-effective configuration (MCU + dynamic tag or NFC frontend)?

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Any advice or experience with similar setups would be highly appreciated. Thanks in advance!

[Peter BENSCH · Accepted solution]

To your questions:

1. An ADC must always use an MCU to transfer data to an NFC tag.

2. As correctly recognised, both devices are slaves and therefore require a master, usually an MCU.

3. Yes, see 1. and 2.

4. The harvested energy is a few milliwatts and can therefore be sufficient for your setup - if all devices, i.e. the opamp and ADC as well as the MCU, are energy-efficient enough.

5. No, a ST25DV cannot read a ST25TV, an NFC reader would be necessary for this, which in turn does not contain an EEPROM and whose energy requirement is significantly higher than the amount of energy that can be harvested.

6. No, there are currently no MCUs from STMicroelectronics with NFC reader functionality.

7. Only ultra-low power MCUs such as STM32L0, STM32L4, STM32U0 or STM32U3 are suitable for operation with the harvestet energy from an ST25DV.

Hope that helps?

Regards
/Peter