M41T62RTC+BMP280+M2402DFC+HTS221.v01z

2 layer board of 0.71x0.31 inches (17.91x7.75 mm).
Shared on April 13th, 2015 03:37.

ST Microelectronic’s ultra-low-power real time clock coupled with Bosch’s BMP280 pressure and temperature sensor and ST’s M2402DFC 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 temperature sensor allows the Teensy 3.1 microcontroller to make periodic calibration updates to the RTC calibration register so the clock remains temperature compensated for maximum (~2 ppm or 1 minute a year) accuracy. The clock outputs the usual date, days, hours, minutes, etc. but also outputs tenths of seconds as well as hundredths of a second.The on-board EEPROM is useful for data logging and storing alarm patterns (music) for output to a small speaker. With 2 Mbits (256 kBytes), lots of data can be logged and dozens of alarm sounds can be stored; one for every occasion! Added Taiyo Yuden PAS3225 2.6V 14 mF super capacitor and Comchip low forward voltage Schottky diode to 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. Added ST Microelectronics' HTS221 16-bit, ultra-low-power relative humidity sensor. The board is now a tiny weather logging station: pressure, temperature, and humidity can be logged once per minute for 15 days!

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