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To create Arduino based device to compare data for as much many t/RH sensors as possible (without manual sensor switch), optionally with data logging for further analysis.

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Use of the same sensor on i2c usually limited by 1 or 2 (using ALT i2c address) of the same type. And SHT20, SHT21, SHT25, HTU21 is actually the same type, so to be able to compare measurement there is a need to use i2c multiplexer. In the case of 8 line multiplexer, there is a possibility to have 8-16 sensor of at the same time to be connected with Arduino.

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Sensor	address	alt address	spec	Vmin-Vmax	Vtyp	1.8v	3.3v	5v**
AOSONG AHT10	0x38 (62)	0x39 (63)	*pdf	1.8-3.6v	3.3v
AOSONG AHT15	0x38 (62)		*pdf	1.8-3.6v	3.3v
Senserion SHT2x	0x40 (64)	0x41 (65)	20,21,25	2.1-3.6v	3v
Senserion SHT3x	0x44 (68)	0x45 (69)	SHT3x	2.15-5.5v	3.3v
Senserion SHT8x	0x44 (68)		SHT85	2.15-5.5v	3.3v
Meas(1) HTU21D	0x40 (64)		HTU21D	1.5v-3.6v	3v
Silicon Labs Si7021	0x40 (64)		pdf	1.9v-3.6v	-
Bosch(2) BMEx80	0x76 (118)	0x77 (119)	680	1.71v-3.6v	1.8v
Bosch(2) BME280	0x76 (118)	0x77 (119)	280	1.71v-3.6v	1.8v
Ti(3) HDC1080	0x40 (64)		pdf	2.7v-5.5v	3v
Ti(3) HDC2080	0x40 (64)	0x41 (65)	pdf	1.62v-3.6v	-
AOSONG DHT12	0x5C (92)		*pdf	2.7-5.5v	5v
AOSONG AM2320	0x5C (92)		*pdf	3.1-5.5v	5v

¹ TE Connectivity Measurement Specialties

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• AHT15 sensors (AHT10 code reuse)
• HDC2080 sensors and code
• connect and enable mux #6

v7 -

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unstable

• stable operation
• hardware RTC clock
• SD files with correct timestamps

v8 - unstable

• Updated Power circuit
• i2c voltage converter board and new wiring
• SHTC1 and SHTC3 sensors added
• mux #1 address changed (to solve i2c address conflict)
• 2x BME680 removed (to solve i2c address conflict)
• 1x BME280 removed (to solve i2c address conflict)
• DHT12 sensors added instead of three BMEx80 (8a)
• ChipCap Sensor added instead of DHT12 (8b)

v9 - current

• AHT20 instead of AHT10
• two HIH7120 added (code reused from CC2D33)
• 3 fan added

v10 - abandoned

• code optimization
• trend visualization
• hardware controls
• menu options (like format SD card)
• got some kind of home-made "calibration" tests with resolutions
• fan
publish final electric scheme, sketch, results

v10-AHT

• New small density sensor boar
• AHT10, AHT20, AHT21, AHT25 sensors only
• exclude voltage conversion (that is why AHT15 is missing)
• a single sensor on one i2c multiplexer lane
• Single read for temperature and humidity data for AHT
• simplified code to support only AHT type of sensors