A Versatile Experiment In Electrical Engineering Technology

An experiment used to implement multi-electrical course knowledge is described. The experiment is an automatic control system in nature with ties to electronics, digital system and computer hardware and software. The idea is to design and build a simple temperature control system, to maintain the temperature inside an enclosed box within a specific user selected range. The plant in this case is the box heated by a light bulb. To monitor the temperature, an LM335 transducer or equivalent is used. The actuator used is a relay switch to control the lamp circuit. Finally, the controller can be analog or digital. It could be a simple operational amplifier comparator or a computer. To emphasize the electronics knowledge, the controller can be built using a window comparator interfaced with a NOR latch for memory. The use of the operational amplifier-latch combination teaches the student how to interface analog and digital parts. A transistor circuit is used to provide the current necessary to energize the relay switch. To provide the circuit with DC power, the students have to design and build a DC power supply. If the emphasis is on computer hardware and software instead of electronics, the controller can be a digital one provided by a personnel computer. The student has to design and build an interface circuit to enable the computer to read the voltage from the LM335 and send a signal to energize the relay. The interface circuit includes an ADC0804 analog to digital converter, a 4N28 OptoIsolator and the PC parallel port. A computer program using C and Assembly languages is written to control the temperature. The designs presented in this paper can be a part of any senior electronics, automatic control, digital systems design, or capstone courses.