[Wizza]

As I gather information and experience with various sensors and cables, and further information comes in below in this thread, I'll continue to update this first post, thereby forming a single place to look for this very relevant information. Do make sure to read through the entire thread below, as you will gather more information regarding cable 'types' and properties, which may also influence your cable choices when building your weather station. I know when starting out on this project, it can all be very confusing and a lot to take in, so hopefully we can address the cable length questions here in one spot.


I2C Sensors - You need to be careful with the length of the SDA, SCL lines, and cable capacitance. The I2C cable between the sensor and the TX board must be very short, with a very good cable 1 meter max. I've read of people having good experience with Cat5 and Cat6 'stranded' cable.

Rain Sensor - I've been testing with a medium duty 14x0.20 figure eight cable with a length of approx 16m and no issues.

Wind Sensor - I'm using a Davis 6410 anemometer, and the factor fitted cable is approx 10m. I spliced on a short 20cm piece of 'flat-4' phone cable at the TX end and crimped on a RJ12 connector, and have had no issues. Note that you need to change the factor fitted RJ12 connector for operation with WeatherDuino PRO2.

Temp/Humidity Sensor - SHT1x / DHT22 - I'm currently running a SHT11 for the external temp/hum sensor. I've used a stranded Cat5e cable (patch lead cable) and currently operation at about 2m length with no issue. I am going to extend this cable to appox 6m, and this should be fine as it does not us the SDA, SCL lines.

Temp/Humidity Sensor - SHT2x - As the SHT2x series of sensors use the SDA, SCL lines, you will be limited to approx 1m cable length.

Solar / UV Sensor - The Solar / UV connector on the TX board does have SDA/SCL lines however they are not used. The Solar / UV interface use only analogue signals. Being an analog signal, we will have to watch cable length and attenuation. A shielded cable, grounded at one end only can also help with analog signals, and is advised. For now I'll start with a short cable or around 2m, and will use a shielded 6-core serial cable with 14x0.20 wires. Will report back with my experience and info.

Regards,

Mark R

[Wizza]

So to focus on the wind sensors, it seems that if you had a FO or similar, with reed switches, then you could run up to 10m or so..????? The Davis 6410 sensor uses a potentiometer type direction sensor, and it comes with about 12m cable, so I guess this kinda confirms that longer cables, up to 10 or 12m should be ok with wind sensors. Does that sound correct...?

[JT118]

It does. Anemometer and vane can run long lengths. It seems, and perhaps Allycat would best to answer this, that sensors with I2C connections are more susceptible to loss than analog sensors and that the simpler the signal (ie rain gauge reed switch on/off) the longer the cable run can be.

nice layout here;

http://mea.com.au/soil-plants-climate/we...r-stations

[AllyCat]

Hi,

Yes, it's generally recommended to limit an I2C bus to about 1 metre, but sometimes it can be pushed further if necessary. Firstly, use twisted pair(s) cable (e.g. CAT5 network cable) not screened/coaxial, to keep the capacitance lower. Pullup resistors (on SDA and SCL) somewhat lower than the normal 4k7 may help; also the software may be able to run the I2C bus in "Slow" mode and/or I believe that bus extender chips are available.

The Rain sensor and Anemometer indeed use simple reed switches, so that long cables (again preferably twisted pair) should not be a problem. However, extending the cables of a "normal" Fine Offset station can cause difficulties, because the transmitter uses a high pullup resistance (to each reed) to save battery power. In this case even a small amount of water (rain) in the cable/connectors can effectively "short out" the switch.

Similarly, the FO Vane uses high value resistances to indicate certain directions so some care may be needed to avoid water ingress. But the "precision" of the FO Vane is such that you probably wouldn't notice anyway.

The Weatherduino Solar sensor uses quite low (analogue) voltages, so the cables should be kept moderately short to avoid "pickup". In this case a coaxial cable might be preferable. If you have to use a long(er) cable, then putting just the PV panel and its load resistor at the far end might be best, because this is a low impedance interface.

Cheers, Alan.

[Wizza]

Ok, been doing a heap of reading, and looks like keep the solar sensor cable to about 1m - 1.2m length.

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Currently testing TX with DHT22 temp/hum sensor. Data sheet seems to indicate a digital output, and I'm reading of people using it up to 20 and 25m on a good cat5 or cat6 cable. So I guess 10 or 12m should be ok..??? And experiences out there..?

[JT118]

Ok, been doing a heap of reading, and looks like keep the solar sensor cable to about 1m - 1.2m length.

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Currently testing TX with DHT22 temp/hum sensor. Data sheet seems to indicate a digital output, and I'm reading of people using it up to 20 and 25m on a good cat5 or cat6 cable. So I guess 10 or 12m should be ok..??? And experiences out there..?

Yes but; Ideally your TX board will be adjacent to your radiation shield so no need to have a long cable. I expect you intend to use an SHT11 or better SHT15. The DHT22 will have a short life span outside particularly where humidity is high.

[werk_ag]

Ok, been doing a heap of reading, and looks like keep the solar sensor cable to about 1m - 1.2m length.

---

Currently testing TX with DHT22 temp/hum sensor. Data sheet seems to indicate a digital output, and I'm reading of people using it up to 20 and 25m on a good cat5 or cat6 cable. So I guess 10 or 12m should be ok..??? And experiences out there..?

10 meters or even more will be ok for an DHT22 or for a SHT1x, but not for a SHT2x.

JT118 already said it on the post above, I'm just reaffirming it:
The DHT22 isn't suitable for long term use for outside readings. Go for an SHT1x or SHT2x depending the cable length you will need.

[Wizza]

As new information comes to hand, or is posted below, I'll keep updating the first post in this thread, forming a single place to look for this information.

Mark R