ST25 ST32 Energy Harvesting + FTM Usage

isaacseeto · ‎2024-09-20

Hi,

I am currently programming a custom PCB with a similar design to the SMARTAG1.

I believe I have correctly enabled FTM and EH_MODE. I have populated the FTM with a test message and checked by reading it back via I2C. EH_MODE has been set to 0.

When I tap my phone, however, NDEF is empty but I was expecting this to have my test message.

Could I please get some clarification on what I am doing incorrectly?

Also, I am assuming the ST25 would output whatever energy it harvests to V_EH and then execute my program. Please correct me if I am wrong.

Thanks.

JL. Lebon · ‎2024-09-22

Hello,

FTM is not used to write NDEF messages.
The usage of FTM is to transfer data between the reader and the microcontroller through the ST25DV. Actually, FTM s using a volatile memory (256 Byte buffer) to store the message that has to be read by I2C. When power is removed (No VCC, no RF field), the content of the FTM buffer (mailbox) is erased.

If you want to store a NDEF message, it has to be put into the EEPROM memory of the ST25DV. This memory is not volatile, and content is preserved over reboot. For this, you don't use the FTM, but simply write into the user memory.

Concerning EH, if you set EH_MODE=0, the ST25DV will output energy on the V_EH pin as soon as it gets energy on the antenna. But RF field must be strong enough to power both the ST25DV and all the devices connected on the V_EH pin. You can check the power on the V_EH pin when the reader is present in front if the antenna to be sure if the RF field allows the output voltage to be high enough to power your microcontroller and other devices.

Best regards.

View solution in original post

JL. Lebon · ‎2024-09-22

Hello,

FTM is not used to write NDEF messages.
The usage of FTM is to transfer data between the reader and the microcontroller through the ST25DV. Actually, FTM s using a volatile memory (256 Byte buffer) to store the message that has to be read by I2C. When power is removed (No VCC, no RF field), the content of the FTM buffer (mailbox) is erased.

If you want to store a NDEF message, it has to be put into the EEPROM memory of the ST25DV. This memory is not volatile, and content is preserved over reboot. For this, you don't use the FTM, but simply write into the user memory.

Concerning EH, if you set EH_MODE=0, the ST25DV will output energy on the V_EH pin as soon as it gets energy on the antenna. But RF field must be strong enough to power both the ST25DV and all the devices connected on the V_EH pin. You can check the power on the V_EH pin when the reader is present in front if the antenna to be sure if the RF field allows the output voltage to be high enough to power your microcontroller and other devices.

Best regards.