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Block diagram of the system

The block diagram is pretty self explanatory. Various types of sensors produce various analog voltages which are shifted and amplified using op-amps in the signal conditioning circuits. The analog multiplexer selects one of these analog voltages and connects it to the A/D converter. The A/D converter digitizes this analog voltage and passes it on to the PC via the parallel port.
A photograph on the next page shows the circuit with its relevant portions demarcated and labelled according to their functions.