I’d like to use a bunch of these to monitor temperature and humidity around the house. Are the any guidelines or restrictions on cable length or characteristics? Longest I’d need would be around 40 meters.
For distance over two meters I would highly recommend that you use a controller to read and transmit the data. Since these sensors communicate via pulse width modulation you could see performance issues at great distances. My recommendation is that you pick up a couple of Versalino’s (you should be okay to get them without the Versalino ports to save a but a piece), and BT2S Slaves.
That would let you monitor anywhere you can get power within 60m – 80m. You can give a direct read method a try, but the nice thing about making a wireless sensor network is you can move the sensors at will, and well… it’s wireless.
Let me know if you need any more info on how to put a wireless sensor network together.
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So here is the break-down of my experience in these areas:
X-10.) This technology transmits low frequency communication signals
over your AC power lines. Though this technology works trying to
integrate it usually requires a proprietary system that takes some of
the control out of your hands, and then there is the fact that you
have to be plugged in and you are introducing a certain level of noise
into your in house power grid.
Zigbee.) The Zigbee is a raw wireless communication board. It is very
popular because it is very open ended, but that serves as a double
edged sword, since in the case of most communication projects having
to deal with the much higher level of complexity required to operate a
raw communications module can make quick implementation very
difficult. On top of that you would need an Arduino, Arduino Zigbee
shield, and a Zigbee for every hub. Not to mention the fact that you
would need at least one Zigbee connected to your computer/project
dedicated to polling data from the other Zigbees in range.
Bluetooth.) This is a 4 wire device Power, Ground, TX, RX, and the
Versalino COM1 port is drop in compatible with it. It uses standard
communication protocols that can be implemented easily on any
smartphone/PC/Mac, or even configured with a BT2S Master to
communicate automatically with another Micro-controller. The ease of
setup and configuration for these devices is why we selected them as
our communication module of choice.
There are certainly a Myriad of devices available that would all be
capable of meeting your general objectives, but I suggest taking the
Bluetooth route because of the Cost control, and easier
learning/implementation curve required.
If you want a challenge, the Zigbee makes for an extremely interesting
system to play with, but it may be costly and time consuming to get to
the point where things are working smoothly.
Hope that Helps!
I´m quite new to arduino.
I was also wondering of max cable lenght….
so I made program which read from data pin (of same dht22) to two different pins of arduino. Wires to one pin were short to other pin were connected through 60m of UTP.
temperatures were same….
Sorry for my english, it´s not my first language
I have had luck with up to 18 inches, but you may be able to push it further. I still recommend using the Versalino Sense & Move, and a BT2S Slave if you want to get a long range on a sensor module.