Ultimate wireless technology for indoor sensors ?

Wireless & IoT
1

My application will be having many different sensors in complex of few building, I would like to cover whole place with sensors. The application requires all these microcontrollers to send the data to the local master microcontrollers. From the local master microcontrollers the data must go to desktop PC via serial connection and from there to a server in the cloud.

I looked at 2.4Ghz modules, but due to being indoor I’m leaning more to sub 1Ghz range. From my online research I conclude that there are two main players; Digi with XBee Pro and Synapse Wireless with Snap. Are there any other manufacturer that I should look at?

Both Digi and Synapse drvices support 2.4Ghz and 900 Mhz ranges, for low bandwidth indoor usage 2.4Ghz is not an option, so 900 Ghz it is.

Both USA and UE have 900 Mhz ISM band, EU is 868 Mhz and USA is 915 Mhz.

Has anybody compared indoor range Xbee Pro vs Synapse Snap on 915 or 868 Mhz ?

Whic is easier to deploy and connect with sensors and microcontrollers ?

2

No experience with the Synapse units but have used the Digi Xbee series 2, 2mW units on 2.4GHz for an indoor sensor network. I found that these work very well even with a WiFi router in the house. These are running the ZigBee protocol and have the ability to ‘relay’ the data through another unit to the ‘coordinator’. So range has not been a problem. I even have two units out in the detached garage. These get relayed by a unit in the attic to the basement where the Host PC collects the data.

These units have a few digital and analog inputs so many sensors can be directly connected without an additional processor. I have one unit on my little Bot that runs full duplex serial communication. Works great even while the other remote units are sending sensor data.

I tried using one of Digi’s base controller units that is internet aware but ended up just writing Python code to run on a PC since I didn’t need to have to access the network through the internet.

Hope this helps.

Have you downloaded and studied the data sheets?

3

If you want to use lots of transceivers, you could use the Nordic nRF24L01+ modules. Here’s a place where you can purchase ten units for $18.99 shipped. I think that’s still less expensive than one XBee module.

http://www.ebay.com/itm/10PCS-Arduino-N … 2781172657

The Nordic modules don’t have all the message hopping and other features the XBees have but you could do all that with software. I’ve used these Nordics to do message hopping myself.

These Nordic modules are also smaller than XBees so you can hide them places where a XBee wouldn’t fit. I keep hoping on making my central air vents motorized with one of these transceivers on each vent so I can better control the temperature of the various rooms.

4

first, decide if you want/need a proprietary wireless protocol and product or one based on an IEEE standard with multiple interoperable vendors. Examples: The dominant home automation wireless today is proprietary to Zensys, licensed as Z-Wave and used by some large companies that sell to retail users. Homeseer.com has an active group on Z-wave.

Other popular proprietary (sole source vendors) are as said above Nordic and TI.

On the standards front, industrial and some smart-energy/grid products use IEEE 802.15.4. The ubiquitous XBee series 1 use that standard which is a brother of 802.11 WiFi. But '15.4 is not the network layer protocol, just as TCP/IP is the network layer most often used with 802.11. In 15.4, many applications use no formal network layer protocol… .they use peer to peer addressing using the MAC addresses of the radio nodes. Any node can be programmed by YOU to relay.

Beyond this, there is ZigBee, a licensed protocol from the ZigBee alliance. It’s all about mesh networking. It’s complex, and is like Bluetooth - a particular use-case profile must be used to get interoperability. XBee Series 2 is >ZigBee only< per a license agreement.

Most of these are licensed $$$. (Bluetooth’s low level MAC/PHY is IEEE 802.15.3 (three) and rarely talked about.

In 15.4, other network protocols include ISA 100.11a (industrial process control), 6LoWPAN, and a couple of others in academia.

I prefer 802.15.4 without a complex network layer protocol. The XBee series 1 is the best choice.

If you need mesh networking vs. DIY relaying, and want to use XBee series 1, consider Digimesh, proprietary but not with the issues of ZigBee.

Range, in any of these, is not magic… just a combination of bit rate, error correction, transmitter power, receiver sensitivity and choice of antennas. The line of sight range can be calculated.

For battery powered devices, the protocol stack has to be carefully chosen so as to enable long battery life with “time synchronized rendezvous” which is the hard part of wireless sensor networks.

5

I have read on couple of other forums that Synapse Snap has much better range than any of 802.15.4, Zigbee or Xbee products out there. Have you used Synapse and compared them? I know about antenna and position issues, but also choice of right spectrum is really important, have you used 900Mhz gear?

6

Beware jargon: You use “ZigBee” and “Xbee” in the same sentence. ZigBee is a network layer - as is TCP/IP. XBee is the name of products that can be ZigBee or not. 802.15.4 is the IEEE MAC and PHY standard used by many products. Synapse does not claim compliance with 802.15.4.

Circuit Cellar magazine has had some recent articles on these. The author isn’t very wireless experienced though.

Synapse is proprietary, sole source. OK for one-of hobby thing but it may not be there next year.

I’ve not used it. But looking at data sheets

Range is affected, mainly, by:

1 Modulation mode and occupied bandwidth. 802.15.4 in 2.4GHz 2MHz channel width,. direct sequence spread spectrum, offset QPSK modulation, 250Kbps raw burst rate = about 80Kbps net without errors. In 868/900MHz, 802.15.4 is quite different; lower speeds, narrower channel. Higher power consumption. FCC regulations in 900MHz require freq. Hopping if the duty cycle is other than tiny.

2 Antenna choices on each end of the link

3 Extent of non-line of sight conditions and details of such

XBee series 1 can be non-mesh or DigiMesh; Series 2 are ZigBee only.

RF100: same specs as most 802.15.4 modules such as XBee Pro Series 1 (Pro has higher power, better receiver).

RF200: Adds other faster bit rates. This will come at the expense of range. Nothing’s free!

RF300: is 868/900MHz. Specs similar to 802.5.14 modules in that band, e.g., the rather pricey sub-GHz XBee.

SM200: about the same as 802.15.4 modules without power amp, i.e., SM200 is RF200 less amplifier and receiver LNA

SM300: same scenario with RF300

SM700: surface mount. Appears to have transmit amplifier but no receive amplifier (LNA)

A good antenna will offset lack of highest transmitter power.

Sub-GHz has about 6dB advantage over 2.4GHz. A 6-12dBi gain antenna at 2.4 GHz more than offsets. Sub-GHz does have slightly less loss in passing through walls, etc. But foliage is about as bad as at 2.4GHz.

So besides these specs, and surface mount vs. through-hole, and not per IEEE, look too at the feature set of the modules’ standard firmware: I/O passing, transparent serial, high speed binary API option, etc. As a hobbyist, consider too the amount of freeware and examples.