Design and consruction of microcontroller-based multi-parameter monitoring system.

Abstract

Many farmers and agricultural research groups need environmental data to augment their agricultural measurements. Such data is needed to understand the physical environment that includes the climate in general, and the microclimate and soils of the area under consideration. An understanding of the environmental variables helps in increasing productivity. Using environmental control it is possible to programme microclimatic conditions so that high value products may be produced.

It is this view that initiated the idea of designing and developing a microcontroller-based environmental data acquisition system for monitoring environmental variables. During this process, an investigation on different types of sensors was studied and the design of low cost sensors was undertaken to replace the commercial types, which are very expensive. It was intended that this system would be cheap, cost-effective and easy to use.

The first stage was to design and construct sensor circuits to be used for measuring the environmental parameters. This was done by identifying the sensors to be developed. The

temperature sensor circuit was the first to be designed using the available materials. The design revolved around the LM335Z sensor to produce a temperature range of –10 oC to +70

oC within ±1 oC. This was followed by the construction of a wind speed sensor. In its design, a thermistor bead was used to measure wind speed from 0 to 10 m/s within ±0.1 m/s. This

was only true under a constant temperature environment of around 25oC. The third sensor to be developed was a solar radiation sensor, which used a solar cell to measure solar

radiation from 0 to1000 W/m2 within ±10 W/m2. The solar cell was recommended because of its availability and reasonable cost. In all these designs the signals produced were

conditioned such that the voltage was in the 0-5V range. This is because the microcontroller, which was used in this investigation, did not accept higher voltages.

The second stage was the design of the main circuit used to measure the analogue voltages to be converted into digital form for display on the seven segment displays. The

environmental parameters measured are displayed, one at a time, with a 5 second separation. The values are also stored on EEPROM at 5-minute intervals. After 85 sets of points, covering over 7 hours, the system begins to overwrite values already stored. At this point, data retrieval should take place through pressing a read button on the front panel of

the system. The heart of the main circuit was the PIC16F876 microcontroller.

The third stage was the development of the software to support the various activities of the system. Calibration of the various sensors was later done in order to enhance the accuracy of the readings. After this, the system was finally assembled.