Final Report for ISL Grant Project 2010 Semester 1
Herbert H.C. Iu
Project Title: Analogue simulators for hand-on learning in the laboratory
Project objectives:
The project aims to develop a compact analogue computer intended for use in undergraduate final year projects. Many students begin engineering study without any practical experience in the subject. Most have never opened up an electronic device, never built one and consider analogue electronics to be archaic and obsolete. The construction of and hands-on usage of an analogue computer is intended to aid in the development of practical skills, deep learning and interest in analogue electronics.
Often in engineering courses, the mathematical equations describing a circuit, the software simulation of the circuit and the physical circuit itself are treated as parallel concepts, making it difficult for students to achieve a broad, encompassing and unified perspective of the subject matter.
The analogue computer links the mathematical description of a system and the system itself. This is of particular use for study of filters, control systems and analogue electronics, in short, real world situations that are subject to physical disturbances and other external or intrinsic phenomena. Further study of a problem using a software simulator provides an important lesson in the differences between physical and simulated systems, including the effects of noise, component tolerances, temperature, EM interference, computer latency and convergence in software simulators.
The analogue computer is not intended to replace circuit modelling software, nor is it designed to provide solutions of exacting precision and accuracy. It is designed to develop student knowledge and understanding of analogue circuitry and its behaviour in comparison to digital and theoretical systems. Students need to understand the differences in results obtained from theoretical calculations, software simulation and physical circuits. They must also understand why these differences occur and which of them are relevant.
Project strategy:
The device is designed to be installed into a Pactec PT-10 enclosure, although any suitably sized enclosure and panel will suffice (Fig. 1). The Pactec design is sturdy, compact, lightweight, cheap and easily obtainable. Panel connectors are banana jacks, which are standard equipment in university laboratories. This means extra patch cords for programming the device should be plentiful if students do not have enough of their own. Power is supplied by a 15VAC power adapter, colloquially called a wall-wart. A rectifier and regulator circuit convert this to +/-15VDC inside the enclosure. Using the adapter means there are no mains voltages in the device and the constructor does not need to deal with any mains wiring.
Inside the enclosure is two printed circuit boards (PCB); one is the power regulator board mentioned above, the other contains the circuitry for the device. The power PCB is a generic design available as a kit from most electronics hobby retailers. The small production volume for this device means this is the cheapest and simplest route to obtaining a bipolar power source.
Figure 1: Compact analogue computer developed
The double-sided analogue circuitry PCB contains a number of operational amplifiers in quad packages, solid state relays, multipliers and associated passive components. The PCB must be wired to the panel mounted components; this is the most time-consuming part of the construction process. IDE connectors are used to connect wiring to the PCB; these are the same as those used on personal computers, hence are very cheap and available from many parts suppliers.
The front-panel is set-up with the jacks for each functional module isolated by distance and/or panel markings. Different coloured banana jacks identify different input and output functions thus helping to streamline the programming phase of any experiment. The panel markings conform to those found on vintage analogue computers; these symbols are still seen on modern schematics and in textbooks so are familiar, or should be familiar, to electronic engineering students.
Project outcomes:
The analogue computer has been developed successfully to simulate physical and mechanical systems without the fiscal expense and time consumed in testing the actual system itself (Fig. 1).
A survey was conducted after the completion of one-year final year project. Twenty project students in our research group using the developed analogue computer completed a questionnaire. Each student was asked to indicate his/her responses to number of statements regarding the course, where each response was limited to one of 5 options: strongly disagree, disagree, neutral, agree, strongly agree. The feedback is generally positive. The majority of the students agreed or strongly agreed that they have developed deeper knowledge and better understanding of analogue circuitry and theory in control engineering. Most of them are satisfied with the experience as well. One journal paper is prepared to submit to IEEE Transactions on Education.
Income
2010 Improving Student Learning Grant $3000
Expenditure
Cases for the analogue simulators $440
Printed circuit boards (PCBs) $500
Labels $120
Other components like capacitors, diodes and resistors $1940