WiFi Extenders

If you have n older Internet router, especially if it does not have WiFi you will probably want to upgrade it to use the latest speeds and frequencies.  You may find it useful to extend the WiFi coverage beyond that provided by the router.  Here are two ways to do that:

Powerline Extender

rendnet and others make devices you can plug into an electric outlet near your router and another one into an outlet further away but on the same electric circuit (ie., the same transformer from the street and service panel) and produce a WiFi access point. We have these installed at Brookfield Farm to provide internet from the router which is upstairs in the office to the sensor gateway which is on the ceiling downstairs and also to the point of sale credit card machine.  Both of these had too much interference to reach the WiFi router because it's next to a metal file cabinet.  

Point-to-point Bridge

This cool device consists of two lrectangular antennas, one connected to your router and one up to 3 km away with good line of sight, pointed at each other to carry the internet signal.  It is the equivalent of stringing a 3 km network cable that far!  My favorite one is The "EZ-Bridge-Lite High Power Outdoor Wireless Point to Point System" which you can find on Amazon for $208.  I have these installed at Provider Farm, Four Town Farm, Fail Better Farm and The Farm School.  They're rock solid and penetrate interference really well.  At The Farm School the signal goes 400 ft through both sides of a barn metal roof on its way from the router to the greenhouse.  They do require standard 120 V power at both ends.

Access Points

The router manufacturers also make range extenders such as this one from Linksys.  A range extender connects to your router via WiFi and retrasmits the WiFi signal and usually have several network ports on it so you can plug a computer into it as well.  We are using one at Simple Gifts Farm to get the router signal to the share barn and provide better WiFi there for the point of sale device.

AA Batteries

In our tests of sensors using AA batteries by far the longest lasting batteries especially in cold weather were Energizer Ultimate Lithium which sell for about $2 each.  The extra cost is well worth it.

12 Volt Batteries


Sensors are usually set to sleep most of the time and only transmit every 15 minutes or so.  That uses so little power that their batteries will last all growing season before they have to be replaced or charged with a USB cable.  However routers and remote gateways require constant power.   Some, use 100 V AC only, others can use a 6 or 12 volt battery and some accept both.  Many vegetable farm greenhouses and, of course, most fields don't have AC power, therefore you will need a deep cycle battery to power the devices.  These are readily available at auto supply stores, recreational vehicle shops and especially marine stores.  (Boaters use them to power trolling motors).   A deep cycle battery's capacity is measured in amp hours (AH).  Higher AH costs more.  A 100 AH battery is about $80 to $120, a 350 AH battery will be $300 to $400.  A 100 AH battery will last 100 hours if your device draws 1 amp at 12 volts, or 1,000 hours if it draws .1 amp however you should plan on recharging the battery when it is drawn down to 40%.  Routers on average draw about .03 amps and gateways about .3 amps.

There are basically three reasonably priced methods for keeping the battery charged:

Swap batteries

By keeping a spare battery charged back at the barn with 110 V AC and swapping the battery in the field, usually every two to four weeks; you may already be doing this for powering remote cattle and deer fence energizers.  Of course you could use the same battery you're using for the electric fence to power a gateway or router.  An electric fence energizer such as the Speedrite 1000 draws 90 milliamps on the fast pulse mode and therefore an 100 amphour battery will last 28 days assuming it is recharged when it reaches 40%.  This figure is computed as follows: 90 milliamp is .09 amp.  100 amphours/.09 amp=1,111 hours.  60% of the hours is 667 hours or 28 days.

Solar panel


Use a solar panel where you get maximum sun.  It must include a charge controller which prevents the battery from being over charged.  You usually have to build a mount of some sort which, of course, must allow for the correct angle from horizontal which can be computed as (latitude * 0.9) + 29 degrees in the winter, (latitude * 0.9) - 23.5 degrees in the summer and latitude - 2.5 degrees in the spring and fall.  (The latitude of Hartford, CT is 41.8 degrees, and Burlington, VT is 44.5 degrees.)  Of course there are many solar panels on the market, but here are some reasonably priced 12 volt units:

Sunforce 50033 15-Watt Solar Charging Kit ($95) available from Amazon, Home Depot and many others; includes charge controller.  We used this near a Brookfield broccoli field to power our Digi X4 Connectport gateway shown here for much of the summer:


Instapark 15W Mono-Crystalline Solar Power Panel With a 12V Charger Controller ($64) from instapark.com or Amazon.  What have not tested this one but it should be just as good.


Thunderbolt Magnum Solar Panel Kit, 45 Watts ($190) from Harbor Freight; includes charge controller for 12 V batteries and socket for cigarette lighter style inverter for 120 V AC, a USB outlet for charging cell phones and an LED display.  We used this to power this 12 V, .5 amp greenhouse muffin fan inflation blower which could, of course, simultaneously power a gateway or router:


Wind Turbine

Use an inexpensive wind turbine such as this www.usawindgen.com Cyber 50 ($80); this is by far the least expensive 50 watt turbine we have found on the market; simple assembly of blades and fin; needs a pole.  Unless it is really windy most of time you would pair this 5 watt or higher solar panel in parallel to the battery especially if it is cloudy much of the time.  Instapark (see above) has a 5 watt version with charge controller for $35.  (We are in the process of testing this combination at Provider Farm.)


Note, if you get loads of clouds and little wind you can always using two or more batteries hooked up in parallel (positive to positive, negative to negative) so that when you do get charging it will last longer.

Powering 110 Volt Devices From 12 Volt Batteries

The MonnitLink Cellular Gateway and Wireless Repeater require 110 Volts AC; you can use a standard 150 watt power inverter with the Thunderbolt Solar Kit mentioned above.  For other situations we're using this cheap (less than $10) combination to convert 12 volts to 110:volts--an inverter from Amazon and a cigaratte lighter to battery adapter from Amazon



Connector to Battery

Connector to Battery


The biggest problem on the farm will be getting your sensors' radio signals to reach the gateway.  There are several methods you can use to extend the radio range of your sensor and routers.

Mount gateway outside

Your gateway computer or Internet router is probably inside your office but most of your sensors may be outside, so you can use a long USB or network cable in order to mount the gateway electronics outside in an enclosure as shown in this picture from Brookfield.  The enclosure is a plastic junction box from the electric department at Home Depot.  Note, it is better to move the electronics out rather that use an antenna extension to some loss in signal.  

Gateway on long USB cable

Gateway on long USB cable

Antenna extension cable

If the sensor electronics need to be near the ground, and your device has a standard RPSMA external antenna connector you can extend the antenna with a 10 ft RP-SMA to SMA Wireless Antenna Adapter Cable from StarTech.com (RPSMA10MF).  Here is an example in a Brookfield tomato fieldhouse where the sensor equipment needed to be near the ground but we needed better line of sight, so we used a $4 piece of 10 ft long 3/4 inch diameter electrical conduit with nylon cable ties to attach the antenna at the top.

Antenna extension cable

Antenna extension cable

Directional antenna

A Yagi antenna such as these focuses and concentrates the signal for better reception.

Yagi Directional Antenna

Yagi Directional Antenna

For 2.4 GHz equipment use this 12 dBi Stainless Steel Yagi Antenna ($50)  from www.l-com.com  (HG2412SY-NF) with this adapter Cable Male-NMale 8' RG-58 RPSMA ($15) from DigiKey.com (item C58LL-RPSM-2438-NM-ND)

For the Monnit 900 MHz equipment use this 12 dBi Yagi Antenna RP-SMA with Plug Connector ($38) from www.l-com.com (item HG912YE-RSP)

Solar Shielding

If placing a temperature sensor where it can be hit by the sun, shield it with this Temperature and Humidity Solar Radiation Shield ($40)  from ambientweather.com (item SRS100LX).

Large solar shield

Large solar shield

Small sensors like the Monnit WIT version can fit in this shield also from ambientweather.com (item MINI-SRS)