For those of us who use Temperature/Humidity sensors outside during the winter in non-desert environments, a high relative humidity is >90%; 50% is pleasantly dry! It matters, because it is stability in the >90% range (and, though to a somewhat lesser extent, below 10%) that 'separates the men from the boys' in the humidity sensor stakes. Do you need stability in near-condensing environments?cdenney wrote: ↑Mon Feb 11, 2019 5:40 pmI'm looking for recommendations for sensors that are high accuracy, fast response (preferably on the order of seconds), and will be reliable over the course of weeks when used in high humidity (>50%) conditions. The accuracy and response rate of the temperature sensor is more important the humidity sensor. The humidty sensor can be anything +/-5% and a response time on the order of minutes would be ok, as long as it is similarly reliable.
True 1-wire is pretty reliable on the Pi.Joel_Mckay wrote: ↑Fri Feb 15, 2019 6:08 amWe found devices with 1-wire are often terrible on anything with dynamic CPU clocking like the Pi. I am constantly surprised how many people don't understand why a polling busy-loop for 1-wire i/o is so wasteful. Such operations can even pin the CPU every-time a DHT style sensor needs power-cycled to recover from hanging every few thousand reads... failures/corruption seems rather random, so people always seem to think... "aha, I solved it this time"... but no... give it a few weeks and you will see the issues again.
True, the example DHT polling libs are usually more likely to have timing issues being invoked from user-space... but its still a hard pass for bit-banging GPIO4 with the kernel 1-wire module (please correct my assumption if something was improved recently)...
Nope, sorry. Been running a number of DS18B20s for years on my Pis now. Occasionally get a bad reading and have code to allow for that and retry. No need for overcomplicating things with extra circuitry.Joel_Mckay wrote: ↑Fri Feb 15, 2019 11:41 amIf you have to go 1-wire, than at least have a look at a protocol converter like the $1.20 DS2482 bridge ( https://www.maximintegrated.com/en/prod ... 2-100.html )... matching 2 successive reads within given precision bounds is also a good idea.
The DHTxx don't mention the 1-wire bus protocol because they don't use it. They use a so called 1 wire interface (ground, power, data line) but it is not a bus based interface and is in no way compatible with the Dallas 1-wire bus.JohnsUPS wrote: ↑Sun Feb 17, 2019 3:17 amI have also found the DS18B20's reliable. I'm also using the OWFS file system and a DS2482 (for driving long distance and to protect the Pi) for reading the sensors, and it works great. No overhead problems. For short runs I'd probably use a GPIO pin (buffered, of course).
The DHT sensor data sheets don't mention the 1-wire protocol because it is proprietary to Maxim/Dallas.