humidity sensor for 5m cable and high humidity

Hey,

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?

Use a second microcontroller and e.g. Serial protocol for the 5 meter. An ATtiny85 will do this job easily.

wvmarle:
Use a second microcontroller and e.g. Serial protocol for the 5 meter. An ATtiny85 will do this job easily.

The ATtiny85 would be betwen the BME280 and the 5m cable or the Arduino and the 5m cable?

BME280 and ATtiny would be close together, then the long cable to the Arduino. Or you could go wireless for that link of course. Whatever you prefer.

phytopia: Hey,

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.

MarkT: How do you know that's not right

Because a BME280 sensor right next to it showed a much lower value.

A wey/dry bulb device is probably doable with a couple of DS18B20's in the metal encapsulation.

Is there something available for Arduino? I didn't find any product.

That's because you'd probably have to make the thing. Google wet/dry bulb hygrometer (or psychrometer apparently - new one for me)

Its just two temperature sensors, one wet, one dry.

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.