Implementation of an FPGA based controller for a propeller clock

Abstract

A propeller clock is a device which displays time in a rather unique way by rotating a strip of LEDs at high speeds and switching them on and off at precise time intervals to give the illusion of a static image being displayed. A static image is seen because of the human eye's phenomena known as persistence of vision. Due to persistence of vision, an image stays on a person's retina for an amount of time even after the image has actually disappeared. The objective of this dissertation was to implement a propeller clock digital controller on a Field Programmable Gate Array (FPGA), whilst keeping the FPGA stationary. An FPGA is an integrated circuit which could be configured using a hardware descriptive language such as Verilog or VHDL. In this work, the digital design was made using VHDL. A stepper motor was chosen to drive the propeller clock because of its accuracy and reliability. A stepper motor is generally referred to as a digital motor because it does not rotate continuously but rotates in steps, where a step is a fraction of a whole revolution. Due to this fact, the position of the shaft is always without the need of any angular sensor. To transfer data from the rotating LEDs to the stationary FPGA a slip ring was used. A slip ring is a mechanical device which is capable of transferring power or data from a stationary unit to a rotating unit. To limit the amount of rings a serial to parallel chip was used and power to the chip and LEDs is provided from a button cell battery. Surface mount components were used because of their small size. Time is also shown on the 4-digit 7-segment display provided on the FPGA development board and can be set by using the push buttons. To display a static image a minimum of 10RPS is needed. Although the manufacturing of the PCBs and slip ring where more of a challenge then expected the propeller clock controller was successfully implemented and tested.