(1)A Microcontroller-Based Data Acq

(1)A Microcontroller-Based Data Acquisition System for Solar Radiation and Environmental Monitoring
(2)Raphael Mukaro and Xavier Francis Carelse
3)Abstract— The hardware design and operation of a battery- powered microcontroller-based data acquisition system (herein referred to as the DAS) for unattended remote measurements are presented.
(4)The system was designed around the ST62E20 8-bit microcontroller and applied for solar radiation monitoring
(5)The measurement system uses the SolData silicon-cell pyranometer as the solar radiation sensor
(6)The data from the sensor is collected by means of on-chip A/D converter and stored in a serial EEPROM until uploaded to a portable computer
.(7) Keeping the DAS in a low-power mode, which is only interrupted when measurements are to be taken or when a computer is connected to retrieve the stored data,
8) minimizes power consumption. An on-chip timer provides an interrupt to awaken the system from its low-power wait mode at 10-min intervals to sample and store the data.
.(9) At the end of each data collection period, the acquired data will be transmitted to the computer through the RS232 serial port for subsequent analysis.
.(10) Only unprocessed data is stored in EEPROM
Quality control and data analysis is done off-line in the laboratory to minimize system cost, complexity and system downtime.
.(12) Field tests and comparisons of this measurement sys¬tem against the standard Eppley precision spectral pyranometer (PSP) have shown a slightly nonlinear correlation and that the accuracy of this measurement system as applied to solar radiation monitoring is fairly good, typically ±13 W/m .
(13)Index Terms—Communication,data
(14)Hence a low-cost battery operated microcontroller-based data acquisition system that runs unattended was developed and applied to continuously monitor solar radiation on a
Manuscript received November 17, 1996
(15); revised September 16, 1999. This work was supported by the United Nations University through the Microprocessor Laboratory, ICTP, Italy.
(16)The authors are with the Physics Department, University of Zimbabwe, Harare, Zimbabwe.
(17)Publisher Item Identifier S 0018-9456(99)09595-9.
(18)need for a stack pointer.
.(19) It was chosen for this purpose because of its low-power consumption, low-cost and an in¬built 8-bit A/D converter with up to 8 single-ended analog inputs.
.(20) The ADC has a conversion time of 70 /is when an 8 MHz oscillator is used.
.(21) With a +5 V supply the converter has a resolution of 20 mV.
(22)Fig. 2 shows the hardware details of microcontroller-based data acquisition system.
(HVe)Fig. 1. Block diagram of the data acquisition system.
(HVe2)Fig. 2. Circuit diagram of the data acquisition system.
(23)each analog input line is verified by connecting the reference voltage, Vref, through one of the switches to the A/D converter.
.(24) A digital conversion is made and the results transmitted to the computer and compared against an expected digital output.
.(25) To ensure optimum system use and minimum power consumption, nearly all control lines of the microcontroller are used effectively.
.(26) Seven lines from port B are used: four (PB1, PB2, PB3 and PB4) for analog inputs and two (PB5 and PB6) for data exchange with the memory chip.
(27)The other port B line, PB0, together with port A line, PA3 are used for RS232 communication with the computer for receiving command messages and for uploading acquired data to the computer respectively.