NFC_temp - accurate passive thermometer in keychain format

What is it?

nfc_temp is a passive NFC tag based on the ATtiny series from Microchip and the dynamic NFC IC RF430CL330H + TMP117 thermometer from Texas Instruments. It measures ambient temperature with a twist; It does not have an independent power source, but is able to be powered by a NFC reader like your phone.

Hold it near the tag and the PCB will siphon some energy from the reader field to power itself and read the temperature from the 0.1 °C accuracy TMP117 thermometer. The ATtiny will compute the temperature value and send it to the NFC IC so the reader can read it in time before the time window for a single read closes.

Note that the PCB needs some time to provide an accurate reading. I advice to let it sit on a table for at least 2 mins.

What makes it special?

• passive design approach, have your phone at hand? read the temperature
• small form factor, similar to a popular 2FA Keyfob, ideal for your analog keychain
• completely open source build stack (KiCad, FreeCAD, Arduino IDE)
• design + production made in Germany

Notes

• Creating the video demo was difficult since the LED strips above are a big heat source so the temperature could not really settle in on the NFC_temp. I did however see very accurate results after letting my keys sit on a desk for a few minutes.