I need a humidity sensor that also works at a cable distance of 5m. I already tried DHT21, however, the humidity levels (inside a greenhouse) were too high, so it showed 99,9%. I also had a BME280 which showed a lower value that seemed more reasonable. However, BME280 is not made to be connected to cables as I've read.
So are there any alternatives for humidity sensors that work in humid environments and on 5m cable?
I need a humidity sensor that also works at a cable distance of 5m. I already tried DHT21, however, the humidity levels (inside a greenhouse) were too high, so it showed 99,9%.
How do you know that's not right - once below the dewpoint the relative humidity is by
definition 100%.
There is a problem with cheap relative humidity sensors - they don't recover from 100% relative
humidity for ages - so they cannot be used in this environment by the sounds of things, they will
not recover after night-time dew conditions fast enough.
A wey/dry bulb device is probably doable with a couple of DS18B20's in the metal encapsulation.
The ATtiny85 method sounds easier. I'm struggling to find anything on how to program it. What is the purpose of the ATtiny85 in this case? Does it alter the DATA signal of the BMP280, so that it is not lost by using a long cable?
The ATtiny would read the sensor over I2C which is a short range protocol, and then use a different communication method to relay this to the main Arduino using some kind of long range protocol. That can be wired or wireless, whatever works best for you.
You can of course also use a separate Arduino instead of the ATtiny. Easier to program, more bulk.
An ATtiny is programmed using the ISP protocol.