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Microcontroller<\/h2>\n\n\n\n
An FRAM-based microcontroller was chosen for its low power consumption and low-cost-per-unit. It also a has a free Eclipse-based IDE<\/a>.<\/p>\n\n\n\n 24 MHz 16-bit MCU <\/p>\n\n\n\n 32KB Non-volatile FRAM<\/a><\/p>\n\n\n\n 4KB SRAM<\/p>\n\n\n\n 420 nA in LPM3.5 (deep sleep mode) with LFXO<\/a><\/p>\n<\/div><\/div><\/div><\/div><\/div>\n\n\n\n MSP430FR2155TDBT<\/a><\/p>\n<\/div><\/div><\/div><\/div><\/div>\n\n\n\n <\/p>\n<\/div><\/div><\/div><\/div><\/div>\n<\/div><\/div><\/div><\/div>\n\n\n\n It is vital that the microcontroller records samples at an accurate time interval<\/a>. This adds fidelity to sample timestamps calculated by the decoder<\/a>. The RC oscillator in the microcontroller is too unstable. This justifies a 32.768 kHz watch crystal, which also reduces power consumption<\/a>.<\/p>\n\n\n\n <\/p>\n<\/div><\/div><\/div><\/div><\/div>\n\n\n\n <\/p>\n<\/div><\/div><\/div><\/div><\/div>\n<\/div><\/div><\/div><\/div>\n\n\n\n The load switch splits cuplTag into 2 power domains:<\/p>\n\n\n\n The cuplTag spends most of its time in sleep mode. It wakes up for a few milliseconds each minute. Current consumption in sleep mode dominates the average, so it must be minimised. The microcontroller is designed to draw ~1.5 \u00b5A in sleep. By contrast, the NFC EEPROM has a very high current, including 10 \u00b5A of leakage through its I2<\/sup>C pins. The load switch fixes this; VMEM is only powered on when the microcontroller is active. Functionality is not compromised: a phone can read or write the EEPROM at all times (it is powered from the field). <\/p>\n\n\n\n <\/a>SIP32431DR3-T1GE3<\/a><\/p>\n<\/div><\/div><\/div><\/div><\/div>\n\n\n\n <\/p>\n<\/div><\/div><\/div><\/div><\/div>\n<\/div><\/div><\/div><\/div>\n\n\n\n Accurate<\/span><\/span> Wide supply voltage range Low peak current<\/span> Factory-installed cover<\/span> <\/a><\/a>HDC2022DEBR<\/a><\/p>\n<\/div><\/div><\/div><\/div><\/div>\n\n\n\n <\/p>\n<\/div><\/div><\/div><\/div><\/div>\n<\/div><\/div><\/div><\/div>\n\n\n\n The EEPROM has two interfaces: <\/p>\n\n\n\n
\n\n\n\nLow Frequency Crystal Oscillator<\/h2>\n\n\n\n
\n\n\n\nLoad Switch<\/h2>\n\n\n\n
\n\n\n\nHumidity Sensor<\/h2>\n\n\n\n
Temperature \u00b10.2\u00b0C (typical) Humidity \u00b12% (typical)<\/p>\n\n\n\n
<\/span>1.62V to 3.6V<\/p>\n\n\n\n
< 1mA<\/p>\n\n\n\n
Protects humidity sensor from ingress<\/p>\n<\/div><\/div><\/div><\/div><\/div>\n\n\n\n
\n\n\n\nNFC + I2<\/sup>C EEPROM<\/h2>\n\n\n\n
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