This schematic represents the acquisition motherboard of a wireless telemetry station for the acquisition of weather and agriculture variables. It comprises analog to digital conversion circuits for sensors in a variety of formats: Voltage, Current, Frequency and Duty Cycle. The format of the sensor signal is detected automatically on connecting the sensor, and several different kinds of sensors can be connected at once on any of the 32 input connectors.

The on board processor, based on a Xilinx FPGA, performs several math processes and builds a data frame to send the data of all 32 sensors allocating 16 bits for each one, and sends the frame twice to facilitate error detection in the receiver station.

This photograph represents the top diagram of the logic inside the Xilinx CPU on the acquisition motherboard. The logic design structure departs top down, from a general structure formed by main functional blocks down to individual math functions inside the blocks. Several hierarchy-nesting levels were necessary to keep control of the complexity of the design.

A strict synchronous method was followed in all design stages, and a precise encoding of time was used to set all sampling and calculation events inside the CPU. The use of Xilinx FPGAs allows executing many processes in parallel, at once, a feature impossible to attain with traditional sequential microprocessors.

These are wireless telemetry stations during assembly in the laboratory. The unit at the top is the acquisition motherboard, the unit at the center-left is a power supply for the RF amplifier, installed on top of the antenna, the unit at center-right is a UHF oscillator based on a digital phase locked loop, capable to generate any carrier from 300MHz up to 500MHz with programmable channels and programmable spacing from 12.5, 25, 50 and 100KHz, and the unit at the bottom is a power supply with a pseudorandom wake-up circuit, to turn ON the telemetry station upon a programmable pseudorandom sequence.

The purpose of this pseudo random sampling rate is to save power between sampling cycles, and to avoid synchronous collisions with other telemetry stations, but any way the average sampling rate remains exactly the same each hour, say 60 samples per hour, or 240 etc. Each station can be programmed to take several thousand samples each day, and as they have no receiver unit, they cannot be interrogated by the central receiving station, they just wake-up, sample, and transmit the data.

Today we have a new CPU with TCP-IP capabilities, that can be accessed from wireless internet, but it has been applied to new projects still under total N.D.A.

This is the schematic diagram of a wired node for networks of soil moisture sensors. The network, buried under the soil, can have 1Km branches, and a maximum of 255 sensors. The structure of the network is hierarchical, with branches and sub-branches, and each sensor can be turned ON and interrogated individually.

The results are shown in the computer screen as a color map indicating the soil moisture at each sensor as a color point.

This network can be also connected to a wireless telemetry station provided a sufficient solar panel surface is available, and a battery with enough capacity to keep the station alive during the night.

This is a central node or "server" for soil moisture sensor networks. The applicatons in agriculture are obvious, but they also have applications in mining. Several networks have been tested under leaching stacks for copper refining.

The sensors, patented in the US (US Pat. # 6,014,029) are rock solid, and have been buried some 20-meters deep under the leaching stacks to measure and control the correct moisture. The sensors measure the dielectric constant at UHF frequencies, covering spectral ranges where the dielectric constant of soil is almost a pure real value with negligible complex part, because the electrolytes are unable to align at that fast pace.

This is the receiver station, during test in the laboratory. It comprises three units, at right, the power supply with some 80 dB line noise rejection beyond 1 MHz, at upper left, a programmable local oscillator based on a digital phase locked loop, capable to scan from 300 to 500 MHz, at programmable channel spacings of 12.5, 25, 50 and 100 KHz. The spectral peak signal to background noise ratio is about 80 dB.

The unit at the bottom left is a logarithmic intermediate frequency amplifier and detector, with an RS-232 decoder. This logarithmic amplifier acts as an "instantaneous AGC " amplifier, capable to receive and process correctly the signals sent by telemetry stations at very different distances at random. For example a station located at short distance, say 500 m, sends a very strong signal followed immediately by another signal sent by a station located at some 15 Km. The logarithmic amplifier is instantaneously adapted to process both signals, because the dynamic range of power covers some 80 dB.

This is a view of the laboratory workbench; during the test of our first telemetry station. At that time, we had just one first telemetry station installed on a hill surrounded by major urban areas of Santiago de Chile at some 9Km distance from our client site, set to 4Watts at 475MHz. Despite of the congested radio spectrum, the signals arrived clearly, and the first sensor files were collected.

There was no clear line of sight between the TX and RX antenna, but thanks to the wide dynamic range of the receiver, the data arrived correctly. The baud rate was set to a conservative 4800 bps in order to avoid bouncing effects on nearby buildings.