Operation
The system works as described here. Upon start-up the system sets up the required internal hardware of the AVR micro and then read the EEPROM memory. If the EEPROM locations contain garbage values then they are set with default values otherwise the previously stored values are read. After reading the EEPROM, the system starts to monitor temperature and waits for actions if any temperature limit is exceeded. The system at this point shows current temperature and system status. If the user wishes to set parameters then he/she has to press the setup button and enter the settings menu. In the settings menu there are three settings and these are high and low temperature limits and the number of passes the system will make prior to issuing a fault message. If, for example, the high temperature limit is set to 40˚C, the low temperature limit is set to 20˚C and the number of system passes is set to 45, and the current temperature gradually rises to 41˚C from 30˚C, the system will trip high temperature alarm and start the cooler. The LCD display will show high temperature alarm. Now if the temperature starts to decline and reach a value in between (40˚C – (40˚C -20˚C)/2) =30˚C [i.e t_delta] and 20˚C within the 45 system passes then the cooler is turned off and no fault message is generated. The system resumes to normal state. If the temperature didn’t decline to the range mentioned as above then it is assumed that the cooler is either faulty or some other thing is causing too much heat generation which is exceeding the cooler’s capacity. Thus a fault warning is issued for the cooler and it is shut down until the fault has been cleared. In this way both the hardware and the cooler is protected from damage. The same scenario happens during the low temperature alarm. If both the cooler and the heater fail then the system goes in a complete halt state until reset or given attention.