Can this sensor be added SHT30 TEMPERATURE AND HUMIDITY S

gloomyandy

@moth4017 What problem would this solve? What issues are you seeing with the existing sensors that are supported?

Adding support for a new sensor will increase memory usage and add to the support burden going forwards so there really needs to be a good reason for doing it. In this case the sensor is also i2c only, on the STM port at least we do not currently support any i2c sensor in the main firmware so this would add an additional burden.

moth4017

@gloomyandy Hi, with the current sensors they are limited to there working temperature , im using them in a dry box/drying box which can get over there operating temperature
:-
STM21 125C max
DHT 80C max
DHT21 80C max
DHT11 50C max
BME280 85C max

gloomyandy

@moth4017 What sensor is the STM21?

I'd be very careful with using any sensor at anything close to the max rating. From the data sheet of the SHT3X:

Stress levels beyond those listed in Table 6 may cause permanent damage to the device or affect the reliability of the
sensor. These are stress ratings only and functional operation of the device at these conditions is not guaranteed. Ratings
are only tested each at a time.

Also from the datasheet:

The sensor shows best performance when operated within recommended normal temperature and humidity range of 5 °C
– 60 °C

and

Prolonged exposure to extreme conditions may accelerate ageing.

Not sure how well that sensor will actually work outside of the specified "normal" range.

What operating temperature do you actually have in this box?

moth4017

@gloomyandy
i have found another sensor but its RS485 , i did see that DC42 had mentioned that some RS485 had been implemented.
But i think the sensor uses the same SHT31 this sensor is rated at 90C ,

gloomyandy

@moth4017 I don't think anything has been done yet for RS485, it is on the the "todo" list. In your previous post you listed a "STM21" sensor, was that a typo?

90C is only 5C more than the existing BME280 so not a very big gain.

Just to be clear, this is just my take on all of this. I don't speak for the Duet3D folks. They may be interested in supporting additional sensors.

oliof

why not use a normal thermistor going above 80-90C? Seems cheaper.

moth4017

@oliof temperature measurement is not the issue its the humidity sensor which does not like being stressed by high temperature, i have found some other capacitive sensors rated at 180C but not found and dev boards that they have been used on, the other option is a humidity sensor from a domestic steam oven need to do more research on these .

moth4017

Seems like all the humidity sensors that can cope with temperatures around the 130C are capacitive type typically around 200pf and need measurement frequency range of 10 kHz, ideally there would need to be a dev PCB to convert to DC 0 to 3.3V or CAN for Duet , i will carry on the search.

@gloomyandy could SPI bus be an option ?

gloomyandy

@moth4017 SPI is the preferred option for sensors attached to a main board (for both Duet boards and the STM32 ones).

deckingman

@moth4017 I'm curious as to why you are trying to measure relative humidity at these elevated temperatures. Given that RH is inversely proportional to temperature, the reading is likely to be at, or very close to, zero in any case. Absolute humidity would be a better indication and it can be calculated from RH but you need pressure and volume as well. Even then, if my memory serves me correctly, the formula for the calculation is only valid for a range of between 5.5 to 12.2 gms H2O/Kg dry air so it's unlikely to yield usable data at very low values.

moth4017

@deckingman Hi im not trying to measure the RH at the HT but i need the sensor to survive the higher temperature , when drying filament at high temperatures the humidity sensor is in the same enclosure . also use it to dry desiccant.