Unit:
Κατεύθυνση Σχεδίασης Ολοκληρωμένων ΚυκλωμάτωνΠληροφορική
Author:
Zafeirakis Ioannis
Supervisors info:
Χατζανδρούλης Σταύρος, Ερευνητής, ΕΚΕΦΕ “ΔΗΜΟΚΡΙΤΟΣ”
Original Title:
Σχεδιασμός και υλοποίηση αναδιαμορφούμενου ενσωματωμένου συστήματος μέτρησης αιθητήρων χωρητικότητας σε FPGA
Translated title:
Design and implementation of a reconfigurable embedded system for capacitive sensor interface using FPGA
Summary:
Smart sensors are used increasingly nowadays for environmental monitoring. A smart sensor is a system which includes apart from the sensor element a processor which enables local processing of the measurements. Within the framework of this master thesis a smart and flexible embedded system for measuring capacitance sensors has been designed and implemented. The system developed comprises of the sensor interface circuit, a LEON3 processor equipped with the necessary peripherals and a Linux operating system. The system implementation is done using a CYCLON series ALTERA FPGA, the Terasic DE2-115 development board and a custom board hosting the sensor elements.
For the measurement of the sensors an interface circuit which converts the capacitance changes in frequency changes by using a specially designed ring oscillator is implemented. Subsequently, a programmable frequency counter featuring a variable measurement time window is used in order to provide flexibility to the measurement time, the accuracy and the range of elaborated frequencies. The interface circuit is connected to the internal data bus (AMBA bus) of LEON3 processor in order to behave as a typical peripheral of the processor and to achieve easy and efficient management from the application software. On the AMBA bus are also connected the standard peripherals of the system, namely, a SVGA touch screen display, a network module (ETHERNET) and a keyboard which give to the system additional capabilities and flexibility. With the embedded Linux operating system the system user can use a standard environment for the processing of the measurements and the communication with the sensors. The user can observe the results on the SVGA display or introduce editing commands from the keyboard. At the same time there is the possibility of a remote connection to the system and the transfer of the results to a remote computer. Programs written in the C programming language are developed for the processing of the measurements and the control of the interface circuit. A stand-allone system has been demonstrated exploiting the capabilities of the "touch screen" display mode and eliminating the need for the presence of a keyboard. The developed software module has the ability to perform sensor calibration and calculation of the mean value and the deviation of the measurements for all channels. To verify the system operation an array of four gas sensors has been used. The capacitive gas sensors consist of interdigitated electrodes and a polymer layer, whose electrical properties vary with the absorption of certain gases (analytes). The response of the proposed system compared to the capacitance measurements using a bridge for various concentrations of analytes has showed satisfactory agreement. The sensitivity of the system is also satisfactory as it can measure very small changes of capacitance resulting to a change of few tens of Hz in oscillation frequency.
The system that was implemented can be used in numerous applications and can be adapted to various environments. By integrating the LEON3 processor which is flexible and configurable, hardware alterations can be easily made and the software can be adapted in order to add extra functionality. Overall, this thesis presents a flexible, stand-alone, easy-to-use and efficient smart system for the measurement of capacitive sensors, which includes multiple processing and communication functions and has many development possibilities. This implementation can be used as a guide for similar implementations in the future and shows the prospects of smart sensor systems.
Main subject category:
Technology - Computer science
Keywords:
LEON3, FPGA, VHDL, EMBEDDED LINUX, smart sensors