Marcin Grajda

Programmable filter for photoacoustic experiments

The paper describes a design, test circuit and preliminary test results of a programmable filter dedicated to photoacoustic experiments. The filter was implemented as a state variable filter with independent digital control of top and bottom corner frequencies as well as quality factor. In order to perform frequency response measurements a dedicated miniature automatic measurement system was designed. The system was based on digital direct synthesis of the input sine wave and true-RMS detection of the output signal.

Low cost miniature data acquisition and control system for photoacoustic experiments

The paper describes a truly miniature system for data acquisition and control, dedicated for photoacoustic measurements. Due to intensive use of electronics and digital signal processing most of expensive and/or inconvenient elements of photoacoustic setups, like mechanical chopper or lock-in amplifier, were eliminated. The advantages of the designed device are very low cost, small size, and high functional flexibility. Most of the measurement factors, e.g. analog path gain, light source modulation frequency, number of samples a period, etc. are programmable and can be changed at run-time. Implementation of real-time and stroboscope PAS signal sampling makes possible to acquire high resolution samples while preserving wide input bandwidth. Due to in-circuit programmable components, upgrades of the device are very easy. Small size and low power consumption make the device a very good choice for implementation of portable photoacoustic instruments.

Behaviour of Altera FPGA circuits working under non-standard conditions

The paper describes different types of behaviour of FPGA circuits working with non-standard conditions (e.g. low supply voltage). Project of experimental board and measurement system, which allows to drive FPGA with specific inputs signals, was presented. Some examples of malfunction FPGA circuits responses caused by non-standard conditions have been shown.

Influence of the pulse duty on photoacoustic signal in Helmholtz resonators

The paper describes experimental results of photoacoustic pulse stimulation of a Helmholtz resonator in which influence of pulse duty factor on the signal amplitude was studied. The signal was measured by means of a dedicated microprocessor system capable of recording the signal shape and frequency response of the cell. Relationship between the light pulse duty factor and signal in the photoacoustic Helmholtz cell at different frequencies is presented.

Application of FPGA devices in implementation of random repetitive sampling oscilloscope

The article describes implementation of Random Repetitive Sampling Oscilloscope based on an FPGA device. The main idea was to achieve high quality instrument at moderate costs. The oscilloscope consists of analogue and digital blocks and most of the digital circuits were implemented in a programmable device, which reduces production costs. Time base and data acquisition circuits are discussed in details. Use of FPGA makes the design more flexible, as changes of the unctionality of the device will not affect hardware. Use of FPGA makes it easy to implement additional functions, e.g. IEEE 488 interface core, if the device is to be use in automatic measurement systems.

PC and virtual-instruments-based lab for teaching of electronic circuits

This paper presents a concept of highly computerized students lab for teaching of electronic circuits. Wide use of modern technologies, like microcontrollers, FPGA chips and computer controlled measurement systems allows to free students from the tedious manual recording of measurements, and let them concentrate on the real investigation of the analyzed circuit. Additionally, due to the limited functionalities and lack of mechanical controls such setup may be a cheaper and more durable alternative for standard lab equipment.

The linearity measurements of the time-base circuit for random repetitive sampling oscilloscope

The paper presents design of a random repetitive sampling oscilloscope time-base circuit. The measurement system based on the pulse generator wih the precise pulse width control functionality is shown. The linearity measurements were performed and employed to verify the time-base circuit design.

B15: Implementation of real time and stroboscobe sampling of photoacoustic signals based on CPLD circuits

Abstract The paper presents implementation of the main digital block of a photoacoustic measurement and control system in which signal processing is performed mainly in digital form. The device produces light source modulation signal and A/D converter control signals. Modulation frequency and number of samples per period of the recorded signal are programmable. The signal acquisition can be performed in real-time sampling or stroboscope sampling mode.

Apparatus to search for optical flashes of extragalactic origin

An apparatus is described to search for optical, point-like flashes in the sky at the time scale of seconds. Such flashes are expected to accompany gamma ray bursts (GRB) observed routinely by satellites and proven to be of extragalactic origin. So far only one such flash has been recorded shortly after the GRB, because standard methods of observational astronomy are not suitable for the time scale of seconds. In this paper, a novel approach is proposed based on experience from particle physics experiments. An apparatus is described which monitors the sky continuously. The large data stream is analysed on-line and potentially interesting events are selected by a multilevel trigger system. In the first phase of the project the apparatus consists of two CCD cameras, especially designed for this project and a robotic mount used to scan interesting regions of the sky. In the second phase the experiment will consist of two sets of 16 cameras on fixed mounts, covering almost all visible sky.