Using white space for communication

Today I came across an interesting article how the white space can be used for internet access in rural South Africa. There are trials in Cape Town (Western Cape) by Google.

Now, Microsoft will team up with University of Limpopo and also look into this ( Read the article on ZDNet).

With "white spaces" one implies frequency space that is allocated to some kind of service (TV, Radio, etc.) but not used allocated. Since the space is not used, it can then obviously be "hi-jacked" for other purposes. Such as for example internet communication and relaying of communication.

In our project we have been looking for ways to have a cheap way of communicating from our sensor stations to the central office (and back). We would like to avoid GSM because of them being rather power hungry and expensive. Could this be an option? As indicated in the article, ranges up to 5.4 km can be covered (metric version of 3 miles, one would presume). For example, in Mokwakwaila, we are not far away from a school and it would possibly be an option to install a communication bridge through their channel. It could also be interesting from an educational perspective to have the students use and understand the information on drought, soil moisture and weather prediction. There could be active labs to support this in the schools.

More information on the Cape Town trials are found here.

Values from Mokwakwaila

The first month's, or so, data from our two sensor stations in Mokwakwaila has now been entered into our spread sheets and published on the soil moisture pages. Notice that the data on the pages need some more trimming. There will also be some comments with respect to what the two different sensors display, etc. Many thanks to Ms Nemauluma who collects the data currently.

Rain at reference site

Yesterday we had a good amount of rain pouring down over Linköping, Sweden. So today is a good day to scan the values in the data logger to further test the equipment and check the levels that were recorded. The graph and data set is given on the soil moisture page.

It started to rain in the morning, at some 09.00 and stopped in the afternoon at some 16.00. During this time, the logger recorded 29 tips, i.e., 29 mm of rain.

In Linköping, an extreme value of 35.2 mm was recorded at one of the SMHI's stations (probably at the airforce base in town, some 5 kilometers away from our site). This means that the values are in parity, but further checking should be done, perhaps with a manual rain gauge too.

Installing a reference sensor

To further develop the readout circuitry and options for the data logger and the sensors, we installed one reference site in Linköping such that we can do local trials. The whole was dug in a lawn, some 50m away from the closest fields. These fields are currently mainly used to grow silage.

We did not dig the hole too deep in this case, we just want to study how the sensors can be calibrated and mainly to interact with the logger through our mobile phones. We will also have reference values available to align with the sensors in South Africa. We dig down three different sensors, EC-5, 10HS, and 5TE from Decagon. The reference values with open-air humidity and fully submerged in water are given in the table. The different sensors give slightly different results but they are also designed for different volumes. Saturated values are fairly identical.

Sensor type	Depth	Open-air [cub-m/cub-m]	Submerged [cub-m/cub-m]	Temp [C]
EC-5	10cm	-0.140	0.574	N/A
10HS	40cm	-0.279	0.505	N/A
5TE-h	60cm	-0.023	0.518	28.7

Some 30 minutes after installation, we could measure these values from the sensors.

Sensor type	Depth	Dug down [cub-m/cub-m]	Temp [C]
EC-5	10cm	0.217	N/A
10HS	40cm	0.210	N/A
5TE-h	60cm	0.020	19.3

Luckily, we got help from a field application engineer to install the sensor and mainly dig. It was also useful to have help when sorting out which cable goes to which sensor. Sort of.

Below we find the final view of the installed sensor station (bar the straps being shortened). There is an ECRN-50 rain gauge from Decagon on the top. It was slightly damaged in a car incident and we have to check if it works properly, otherwise we need to ship it for service.

We need to also verify the ECRN-50 rain gauge.