HDC2021: HDC2021 not returning MSB of temperature

mike leggett

Part Number: HDC2021

I can correctly read the device ID from the HDC2021 with the MSB returned as 0x07 and the LSB returned as 0x0D, as well as the manufacture id as 0x5449

But the MSB of the temperature (address 0x01 returns a constant which varies. The LSB read returns data than moves and rolls over with temperature as expected.

A read of register x04 prior to reading the temperature returns data = 0x80 => data is ready.

I sent a soft reset to the device (addr 0x0E = 80) and and I got the same results.

The timing minimums exceed twice those in the data sheet. Clock speed is 189Khz.

The humidity sensor is returning reasonable data which varies with temperature changes which are likely changing the humidity, so I suspect it is operating.

over 2 years ago

0 Pavani Deepthi Tenneti over 2 years ago

TI__Expert 3270 points

Hi,

Could you share the code to read the temperature and humidity from the device? Could you also read register 0x0F and check if both the temperature and humidity measurement has been enabled?

Regards,
Pavani Tenneti

0 mike leggett over 2 years ago

Prodigy 80 points

Register 0x0F gets data = 0x01, which should start conversions on both the temperature and humidity. the zeros in bits 1 and 2 enable both the temperature sensor and humidity. You can see these bits in the wave forms I sent you.

Here are the bytes that are sent which match the wave forms I have sent you.

CONSTANT HDC_BYTE_1 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"80" ; -- HDC2021 DEVICE ADDRESS WRITE
CONSTANT HDC_BYTE_2 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"0F" ; -- HDC2021 START CONVERSION COMMAND ADDRESS
CONSTANT HDC_BYTE_3 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"01" ; -- HDC2021 START CONVERSION COMMAND (9 BIT AND START)

CONSTANT HDC_BYTE_4 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"80" ; -- HDC2021 DEVICE ADDRESS WRITE
CONSTANT HDC_BYTE_5 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"01" ; -- HDC2021 TEMPERATURE ADDRESS
CONSTANT HDC_BYTE_6 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"81" ; -- HDC2021 DEVICE ADDRESS READ
CONSTANT HDC_BYTE_7 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"FF" ; -- HDC2021 READ TEMPERATURE DATA. PULLUP SO DEVICE CAN DRIVE ZEROS

CONSTANT HDC_BYTE_8 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"80" ; -- HDC2021 DEVICE ADDRESS WRITE
CONSTANT HDC_BYTE_9 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"03" ; -- HDC2021 HMIDITY ADDRESS
CONSTANT HDC_BYTE_10 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"81" ; -- HDC2021 DEVICE ADDRESS READ
CONSTANT HDC_BYTE_11 : STD_LOGIC_VECTOR(7 DOWNTO 0) := X"FF" ; -- HDC2021 READ HMIDITY DATA. PULLUP SO DEVICE CAN DRIVE ZEROS

0 Josh Wyatt over 2 years ago in reply to mike leggett

TI__Guru* 91086 points

Mike -

Here, after starting a conversion and then waiting for ~1.3mSec, then reading 0x04 for 0x80, you can set pointer to 0x00 and read out all four bytes for temp and %RH at once - please see our FAQ on this topic and let us know if it helps you out.

https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/878721/faq-hdc2080-hdc2010---i-am-getting-incorrect-values-for-example--40c-or-0-rh-or-both-from-hdc-device-for-my-first-read-or-for-any-read-how-to-troubleshoot-the-problem?tisearch=e2e-sitesearch&keymatch=HDC2080#

0 mike leggett over 2 years ago in reply to Josh Wyatt

Prodigy 80 points

Josh,

I am waiting 1ms against a typical of 640us.. I will increase it but doubt its the problem. I was just looking for the MSB and had address 0x0F = 0xa1. changed it to 0x01 just to increase the visibility of what is going on. Yes I could just read all four bytes in a row and throw out the two LSB's.. about the same either way, right? I will try the auto increment.

0 Josh Wyatt over 2 years ago in reply to mike leggett

TI__Guru* 91086 points

Mike - in this case, if you are reading both temp and %RH, you have to add the conversion times, which for 14 bit result (which is default) is around 1.3mSec. You should not have to throw anything away. If not using the DRDY/INT line from the part to trigger read of register 0x04 I would wait around 1.5mSec, to cover over temp operation.

0 mike leggett over 2 years ago in reply to mike leggett

Prodigy 80 points

I increased the wait time to 2ms. still no MSB temp data. The present form of my reads works for your device ID and Mfg ID. Why wouldn't it work for the tempeature?