Power Supply Chose to use lithium polymer batteries over nickel-metal hydride because of higher energy density –Higher energy density = Smaller size, less weight Using switching voltage regulators because of high efficiency –Decided to use a self-contained package to avoid having to calculate values for external components and to keep size small.
Sensor System Used same components as our previous mouse since we were familiar with it. –Sharp GP2D120 sensors and Maxim MAX114 analog- digital converter. Decided to use a different sensor configuration. –Using four sensors instead of three, two outer sensors on outside point straight forward to help align during a 45 degree run.
Motor Control PWM –We chose to use Pulse Width Modulation to control the speed of the motors because it is simple to implement. H-Bridge –H-bridges will be used to control the direction of the motors. Encoders –We chose to use optical encoders to help determine the position of our mouse.
PWM A pulse-width modulated signal is a rectangular waveform with a varying duty cycle. A longer duty cycle means the voltage is on for longer and the average voltage applied to the motor is higher and vice versa. Will be implemented using the PWM generator on our microcontroller.
H-Bridge DC motors only have two leads. The direction it spins is determined by which terminal has power applied and which is connected to ground. An H-bridge consists of four switches (in our case BJTs) and depending on which two are closed, allow the motor to operate in either direction We chose to use an L298 chip from STMicroelectronics because it has two H-bridges in one package.
Encoders We decided to use optical encoders over accelerometers. –Accelerometers were harder to implement, and may not have been accurate enough. –If the mouse was not accelerating or decelerating, we would have had to assume and calculate our position The optical encoders give us a more definite position reading. We chose the HEDS-9100 encoders because of size limitations.
Microprocessor Rabbit 3100 Core Module –Uses a Rabbit 3000 microprocessor. Software P.I.D Controller –A software Proportional-Integral-Derivative controller is a feedback system that will allow us to more accurately control our system.
Rabbit 3100 We chose the Rabbit 3100 over other microprocessors. –Other models we researched would have been harder to implement. –Chose the Rabbit 3100 because we could reuse our programming cable and it had pulse-width modulation capability. –Also found that it had quadrature decoders which help us to use the encoders.
Software P.I.D. Controller Motors are not a digital type of device. A sharp change in voltage level doesn’t instantly change the speed of the motor. We have to take this time constant into consideration. We will use a PID controller to fine-tune the operation of our motor. Takes readings and calculates an error value. Tries to get the system to settle at the correct value as quickly as possible. A PID controller modifies the error signal in three ways to determine the best correction. Still needs to be implemented and fine-tuned…
Proportional – Integral – Derivative The proportional part of the modification is simply multiplying the error signal by a constant to adjust for the current error. The integral part of the modification is multiplying the error signal by the result of an integral to adjust for error in the past that hasn’t been corrected yet. The derivative part of the modification is multiplying the error signal by the result of a derivative to try and predict the future error correction required. The sum of these corrections (once the constants have been fine-tuned) should be a system that reaches an accurate steady state as soon as possible.
Tracking, Mapping, Solving Using old code, modified for this mouse. Plan on possibly implementing different solving methods. Plan to implement a few modified flood-fill (Bellman) algorithms
What remains to be done… Connect PCB board to external modules Programming the mouse Fine-tune PID controller Troubleshooting / Debugging Write up our 30 page paper