EnvironmentalDataLogger.v05

4 layer board of 0.71x0.31 inches (17.91x7.75 mm).
Shared on October 3rd, 2015 07:15.

ST Microelectronic’s M41T62 ultra-low-power real time clock coupled with Bosch’s BME280 pressure, humidity, and temperature sensor and ST’s M2402DRC 2Mbit EEPROM in an appallingly small add-on board for Teensy 3.1. Power is supplied via digital write to general GPIO pins since the total power requirement never exceeds 2 mA. Communication is via I2C and there are 4K7 pullup resistors on board. The 512 Hz square-wave output allows the Teensy 3.1 microcontroller to make periodic calibration updates to the RTC calibration register so the clock is continuously compensated for maximum (~2 ppm or 1 minute a year) accuracy. The Taiyo Yuden PAS3225 2.6V 14 mF super capacitor and 1N4148 diode provide power to the RTC time keeper even when disconnected from the microcontroller. The PAS3225 5 microAhour super cap can run the RTC (which needs ~330 nA at 2.6 V) for about 18 hours. The board is now a tiny weather logging station: pressure, temperature, and humidity can be logged once per minute for 15 days! Went back to standard 1N4148 diode.

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