Thoughts on Wireless

Wireless is only recommended for the more advanced users, since they are more difficult to understand and troubleshoot. Wireless is also a poor choice for very large displays.

There are three main types of wireless controllers used for lighting.

  • XBEE – Nominally in the 800-900Mhz band
    • Used for incandescents and dumb RGB lights
    • Low channel counts
  • Komby (NRF24L01) – WiFi band plus 2.400-2.525 GHz
    • High cost for transmitters
    • Support large channel counts
    • Shares space with WiFi
  • ESPixelStick (ESP8266) – WiFi bands only
    • Uses wireless router to transmit
    • Low cost receivers
    • Supports high channel counts
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WiFi Background Noise

This is the first year, 2015 for the ESP8266 devices, so I would wait a year to ensure that they are reliable in a crowded WiFi environment. There are only three WiFi channels, which are often well used in suburbia.

KOMBY

The NRF24L01 transceivers use the  same frequency space as WiFi plus some, there are a total of 125 channels. Channels 83-100 are restricted by the FCC are should not be used. The picture shows the background noise that I measured in my house over more than 24 hours. In the picture I have labeled the three main WiFi channels. As shown in the picture a little less than half of the usable RF channels are covered by WiFi. There is also noise from your microwave oven, with the main operating frequency being around 2.45Ghz. Also, if you have cordless phones in the house, they are often in this frequency band. The channels used by WiFi are listed below.

  • WiFi channel 1. NRF channels 1-23
  • WiFi Channel 6, NRF channels 26-48
  • WiFi Channel 11, NRF channels 51-73
  • WiFi restricted space channels 83-100

For the wifi transmitters, if you use the nominal channels of 1,6, and 11, the routers will share the transmission time/space. So if you are the only one on the channel your data will all be transmitted on time. If you are sharing the space, the time that your data is sent out will depend upon how heavily the other routers are using that particular channel. For me this makes the ESPixelStick less appealing for those in a congested wifi environment.

The wifi band is an open standard, so how do all of these work when you have over lapping frequencies? Basically, all of the transmitters are limited in how much power they transmit. This along with the attenuation provided by the walls of the houses and the distance between the various routers allows them to all work in the same frequency band. I liken it to a shouting match, where your devices are loudest in your own house, and hopefully the neighbors don’t hear.

Maximizing the signal involves two steps. First understanding the antenna pattern of the transmitter. If you hold transceiver upright in front of you with the pins at the bottom and the PCB traces for the antenna at the top. Imagine dropping a doughnut over the circuit card. This the shape of the antenna pattern. There are nulls or low gain points in the antenna pattern at the top and the bottom and you do not want your transmitters or receivers to work through these low gain points. So always position the antennas in a up or down vertical position. For those using the high power transceivers, the antenna pattern is the same, so ensure that the antenna points up/down.

The second point to maximizing signal is minimize the material that the signal has to pass through to the receivers. So ideally, you would have line of sight between the transmitter and receiving antenna’s. My happy thought, would be to place the transmitters under the mega-tree, which is most likely in the center of your yard. The next best place would be in a window in your house. If your house is made of stucco, you might want to think about moving the transmitters outside or into a window. Also note that the low E coating on your window is a good signal attenuator. Below is a list materials with the measured attenuation, so the actual attenuation would be composite of the materials in the wall of your house.

Attenuation for different materials

  • Material                       Attn db      % of Signal Passed
  • 0.1″ plexiglass              -0.005                99.9
  • 0.56″ ceiling tile          -0.1                      97.7
  • 0.3″ plexiglass             -0.36                    92.0
  • 0.1″ glass                        -0.5                      89.1
  • 0.5″ drywall                  -0.5                      89.1
  • 0.75 particle board    -1.7                      67.6
  • 0.75 plywood               -1.9                      64.6
  • 1.5″ doug fir                  -2.8                      52.5
  • 4″ thick brick                -4.5                      35.5
  •  8″ cinder block            -7.0                      20.0
  • 1″ stucco                         -14.7                    3.4
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