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Electronic Control System

The electronic systems of the underwater robot consist of its electronic control system, a solar panel, two battery power supplies, and the electro-mechanical solenoid valves used in its buoyancy and resurfacing systems. Since the team choose to design the robot to drift with the current rather be self-propelled and to use a third party sensor package, the amount of electronics needed to control and operate the robot were greatly reduced. It was also desired to keep the number of electronics to a minimum in order to increase the reliability of the entire system.

Initially, team 6 opted to use a very simple circuit composed of a transistor, battery, solenoid valve, and solar panel for the resurfacing system. The idea behind the resurfacing control circuit is that the transistor would act as a switch between the battery and the solenoid valve that would open when it detected a significant voltage coming form the solar panel.

Since team six was composed entirely of mechanical engineers the buoyancy control system was the last of the systems to be designed and constructed. The team decided to restrict the control system to a simple timing mechanism which would activate the solenoid valves in a predetermined order that would cause the buoyancy of the robot to oscillate at fixed intervals. After consulting with an electrical engineer, who wishes to remain anonymous, it was determined that the best options were to use either a 555 timing circuit or a microcontroller in conjunction with an interface board.

A 555 timing circuit is an electrical RC circuit that is constructed around 555 integrated circuit that produces a regulated timing pulse. This pulse is then manipulated and used by the RC circuit to produce a number of results based on the type of circuit including a timed cycle of pulses to multiple outputs. Some of the main features of a 555 timing circuit are that they are inexpensive, very accurate of short time periods, and all the “programming” is done by physically modifying the circuit.

        After further consultation with the electrical engineer and clarifying what tasks the control system would need to perform a 555 timing circuit was deemed unsuitable. 555 timing circuits tend to become very inaccurate over time periods longer than a few minutes and the basic valve activation scheme that had already been decided upon called for wait periods of over an hour. The remaining option was to use a microcontroller in conjunction with an interface board. The electrical engineer offered to help with the selection, construction, and programming of both components. After the decision was made to use a microcontroller the group decided to integrate the resurfacing and buoyancy control systems.