"The status and temperature date saved to PC via serial communication. Here 8 temperature sensors are connected(4 shown in diagram for simplicity). values of all the sensors are sent serially by AT89C51 to pc. Software "DAQ System " takes these values and show them on its front panel, and also logs them to the data base "daq.mdb" .we can set some parameters like set point , low limit ,and high limit . when temperature of some sensor increases beyond set point ,the heater connected to controller (specific for that sensor) will be turned OFF( ON in opposite case ).High limit and low limits are for alarm. when temperature goes above high limit or below low limit the alarm will be turned on."
For complete reference, source code, Schematic, you can download here.
[Link]
