Temperature and humidity sensors for weather data.

Community Projects
1

Hi

I would like to set up temperature and humidity sensors for weather stations that I plan to set up for many people to enable more online data where it is currently not recorded. I want the sensors to output a voltage range of between 0 and 5 volts to log the voltage on the computer and then use Microsoft Excel to calculate the temperature and humidity. Is there a simple low cost circuit board made up where the sensors can be connected to enable this output and can you find a specific circuit board for me? I would like to set -10°C as 0 volts and 50°C at 5 volts and have a linear range in between.

For humidity, I would like to set the lowest humidity the sensor can measure as 0V and 100% as 5 volts. I would like to get a humidity sensor that can go down to at least 10%. I am also wondering how accurate humidity sensors are and if there are any more accurate low cost ones than what I link below. I plan to order from https://www.auselectronicsdirect.com.au for another product so it may be best to order from them. I could get the sensors on the below links. The last link suggests a few temperature sensors and I wonder which is most suitable.

https://www.auselectronicsdirect.com.au … ture-probe

https://www.auselectronicsdirect.com.au … z5EALw_wcB

https://www.auselectronicsdirect.com.au … ure+sensor

Regards Richard.

2

For temperature, the DS18B20 (your first link) is a good sensor. There are many articles on the internet for that and it uses a onewire interface.

For humidity: there are different ways to measure humidity: resistance or capacity. Many use the BME280 which is using capacity. If that is exposed for a long time to high humidity it will provide incorrect information for some time after. (see an earlier post on: viewtopic.php?f=74&t=59039) It looks better to use EFS-10 or another thermistor device where the resistance changes based on humidity. A nice article (+ reference to a circuit & sketch) is on: https://forum.arduino.cc/t/advice-on-ho … r/133464/6. There they used an LM335 for temperature measurement.

3

Hi

I should have also mentioned that I am currently using the LM335Z temperature sensors and they work quite well. However, they are not waterproof and I had trouble with water entering them even if they have been sealed in heat shrink. I can still use them in many places so I would like a circuit board suitable for them as well. There is more information on them at https://pdf.datasheetcatalog.com/datash … LM335Z.pdf

Do you think they are similar to the DS18B20 water proof temperature probe at https://www.auselectronicsdirect.com.au … ture-probe regarding the wiring and linear output so that hopefully they will work on a similar circuit board?

Do you think there is a good chance I may find a low cost circuit board to simply connect to the sensor so it would set -10°C as 0 volts and 50°C at 5 volts and have a linear range in between? Please let me know if you find a circuit board for this.

A problem is the EFS-10 humidity sensor only measures between 20 and 95 %. My humidity can range from 10 to 100. Are there any accurate sensors that can measure that range?

Regards Richard.

4

The DS18B20 is a good sensor. It is waterproof so it can be used in wet environments, but I would not put it under water. not sure it is IP67. There are good descriptions of the onewire interface. There is also a good chip from Sensirion (they make good products) with an SHT-30. It does BOTH temperature and humidity. e.g. look at https://wiki.dfrobot.com/Digital_Temper … U_SEN0148_ but there are many others that use this chip. The communication is I2C.

5

I want the sensors to output a voltage range of between 0 and 5 volts

This is going to be a challenge as most sensors these days are digital and don’t provide an analog output. Even if you can find an analog sensor, chances are good it doesn’t put out a 0-5 volt signal and it probably won’t be zero to VCC between the setpoints you’re looking for.

What you’re probably going to need to do is connect your digital sensor of choice to an Arduino and have that manage reading temperature from the sensor then doing a bit of math to that reading to determine what voltage you’re wanting to output. Then, you can attach a DAC (digital to analog) converter to your Arduino and instruct that to output the analog voltage you’re desiring. That would maintain compatibility with your current setup but if you were able to go full digital, you could just log the data coming right out of the sensor by printing it and then using something to log your output.

If you’re interested, the tutorial below might help get you started.

https://randomnerdtutorials.com/guide-f … h-arduino/

6

Hi

The LM335Z temperature sensors connect to a simple circuit that a man made up for me so they do what I want which is -10°C at 0 volts and 50°C at 5 volts and have a linear range in between. Are you suggesting that most other temperature sensors are different and would be more complicated and time consuming to set up to do what I want or require a more expensive circuit? I wonder if they would include the DS18B20 water proof temperature sensor?

Regards Richard.

7

I never mentioned it being more expensive or more time consuming, but other than that, yes. New sensors are almost always digital rather than analog. You might consider using them digitally rather than trying to make them produce an analog output. (Which would be more complex but it is doable)

8

Are the LM335Z temperature sensors digital or are they analogue? I could not find any info about this on another file at https://www.jaycar.com.au/medias/sys_ma … etMain.pdf .

Regards Richard.

9

They are analog.

10

Are the DS18B20 water proof temperature sensors digital or are they analogue?

11

From the [datasheet:

General Description

The DS18B20 digital thermometer provides 9-bit to

12-bit Celsius temperature measurements and has an

alarm function with nonvolatile user-programmable upper

and lower trigger points. The DS18B20 communicates

over a 1-Wire bus that by definition requires only one

data line (and ground) for communication with a central

microprocessor. In addition, the DS18B20 can derive

power directly from the data line (“parasite power”),

eliminating the need for an external power supply.

Each DS18B20 has a unique 64-bit serial code, which

allows multiple DS18B20s to function on the same 1-Wire

bus. Thus, it is simple to use one microprocessor to

control many DS18B20s distributed over a large area.

Applications that can benefit from this feature include

HVAC environmental controls, temperature monitoring

systems inside buildings, equipment, or machinery, and

process monitoring and control systems.

Applications

● Thermostatic Controls

● Industrial Systems

● Consumer Products

● Thermometers

● Thermally Sensitive Systems](https://www.analog.com/media/en/technical-documentation/data-sheets/DS18B20.pdf)

12

Do you think it would probably be better to stick with the LM335Z temperature sensor based on my requirements which is -10°C at 0 volts and 50°C at 5 volts and have a linear range in between? I am hoping to find a simple circuit made up to output the voltage range. The man that made the circuits for me is not able to make any more. It would be good if we could find one for sale made up that would do what I want with only maybe small adjustments. Is that likely?

Alternatively I wonder if there is a simple circuit sold made up to make a digital sensor like the DS18B20 do what which is -10°C at 0 volts and 50°C at 5 volts and have a linear range in between.

Regards Richard.