pkg dhtxx: reports wrong temperature value if cold (T

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#pkg dhtxx: reports wrong temperature value if cold (T < 0°C)

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kaxori 12/28/2024 06:21 PM

if temperature gets negative it returns wrong values:
T: 0.00, H: 64.60
T: 3276.90, H: 64.60

reason might be here:

parse_temperature_ data/ByteArray -> float:
    return (BIG_ENDIAN.uint16 data driver.Driver.TEMPERATURE_INTEGRAL_PART_) / 10.0

=> it works, but I think could be done nicer:

parse_temperature_ data/ByteArray -> float:
    return not (driver.Driver.TEMPERATURE_INTEGRAL_PART_ & 0x8000) ? 
      (BIG_ENDIAN.uint16 data driver.Driver.TEMPERATURE_INTEGRAL_PART_) / 10.0 :  
      -((BIG_ENDIAN.uint16 data driver.Driver.TEMPERATURE_INTEGRAL_PART_) & 0x7ff) / 10.0

(edited)

OPkaxori

if temperature gets negative it returns wrong values: T: 0.00, H: 64.60 T: 3276.90, H: 64.60 reason might be here: ``` parsetemperature data/ByteArray -> float: return (BIG_...(edited)

floitsch 12/28/2024 07:33 PM

So the first bit is a sign bit?

kaxori 12/28/2024 07:34 PM

yes, but I still struggle with correct boolean expression

floitsch 12/28/2024 07:35 PM

I will fix the package when I'm back from vacation. Please post a few values you get from the sensor so I can verify that the new code will work

kaxori 12/28/2024 08:15 PM

DHT data: #[0x02, 0x61, 0x00, 0x01, 0x64]
333: T: 0.10, H: 60.90
DHT data: #[0x02, 0x61, 0x00, 0x00, 0x63]
334: T: 0.00, H: 60.90
DHT data: #[0x02, 0x62, 0x00, 0x00, 0x64]
335: T: 0.00, H: 61.00
DHT data: #[0x02, 0x63, 0x00, 0x00, 0x65]
336: T: 0.00, H: 61.10
DHT data: #[0x02, 0x64, 0x00, 0x00, 0x66]
337: T: 0.00, H: 61.20
DHT data: #[0x02, 0x65, 0x00, 0x00, 0x67]
338: T: 0.00, H: 61.30
DHT data: #[0x02, 0x64, 0x80, 0x01, 0xe7]
339: T: -0.10, H: 61.20
DHT data: #[0x02, 0x64, 0x80, 0x01, 0xe7]
340: T: -0.10, H: 61.20
DHT data: #[0x02, 0x63, 0x80, 0x01, 0xe6]
341: T: -0.10, H: 61.10
DHT data: #[0x02, 0x61, 0x80, 0x01, 0xe4]
342: T: -0.10, H: 60.90
DHT data: #[0x02, 0x60, 0x80, 0x02, 0xe4]
343: T: -0.20, H: 60.80

kaxori 12/28/2024 08:17 PM

Hope you have cold enough temperatures then.
enjoy your vacation.

kaxori 01/02/2025 07:45 PM

you changed only the import

import io show BIG_ENDIAN

I do not understand why this change removes the error. Could you please help me .

floitsch 01/02/2025 07:46 PM

The PR with the fix hasn't been committed yet: https://github.com/toitware/toit-dhtxx/pull/12(edited)

Fix negative temperatures by floitsch · Pull Request #12 · toitware...

The DHT22 supports negative temperatures which weren't read correctly.
Fixes #10.

kaxori 01/02/2025 07:47 PM

floitsch 01/06/2025 11:15 AM

A new version of the package has been published.

10 messages in total