avsa242 / htu21d-spin

Parallax P8X32A/Propeller, P2X8C4M64P/Propeller 2 driver object for the Measurement Specialties HTU21D Temp/RH sensor

htu21d-spin

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This is a P8X32A/Propeller, P2X8C4M64P/Propeller 2 driver object for the HTU21D Temperature/RH sensor.

IMPORTANT: This software is meant to be used with the spin-standard-library (P8X32A) or p2-spin-standard-library (P2X8C4M64P). Please install the applicable library first before attempting to use this code, otherwise you will be missing several files required to build the project.

Salient Features

• I2C connection at up to ~30kHz (P1: SPIN I2C), 400kHz (P1: PASM I2C, P2)
• Read temperature (hundredths of a degree), humidity (hundredths of a percent)
• Enable optional CRC checking of data - read flags indicating last acquired data was valid
• Set sensor resolution
• Enable on-chip heater (intended for diagnosis only - 0.5-1.5C temperature increase)
• Read low-battery status

Requirements

P1/SPIN1:

• spin-standard-library
• 1 extra core/cog for the PASM I2C engine (none if SPIN I2C engine is used)
• sensor.temp_rh.common.spinh (source: spin-standard-library)

P2/SPIN2:

• p2-spin-standard-library
• sensor.temp_rh.common.spin2h (source: p2-spin-standard-library)

Compiler Compatibility

Processor	Language	Compiler	Backend	Status
P1	SPIN1	FlexSpin (5.9.23-beta)	Bytecode	OK
P1	SPIN1	FlexSpin (5.9.23-beta)	Native code	OK
P1	SPIN1	OpenSpin (1.00.81)	Bytecode	Untested (deprecated)
P2	SPIN2	FlexSpin (5.9.23-beta)	NuCode	FTBFS
P2	SPIN2	FlexSpin (5.9.23-beta)	Native code	OK
P1	SPIN1	Brad's Spin Tool (any)	Bytecode	Unsupported
P1, P2	SPIN1, 2	Propeller Tool (any)	Bytecode	Unsupported
P1, P2	SPIN1, 2	PNut (any)	Bytecode	Unsupported

Limitations

• Very early in development - may malfunction, or outright fail to build
• Low battery status flag unverified
• P2 demo has incorrect output when built with FlexSpin 5.9.13-beta or older: see FlexSpin issue #289.

htu21d-spin's Issues

Support compile-time selection of I2C engine (P1)

For applications where data acquisition speed isn't as critical, but memory usage is, support for the SPIN I2C engine should be added.