Development of a low-power-signal acquisition device for signals lower than 25 Hz

Table of Contents

1. Assignment

2. Concepts

2.1 Using the sound board of a personal computer

2.2 Using the USB-Interface

3. Low-pass-filter

3.1 Motivation to use a low-pass-filter before digitizing

3.2 Kinds of low-pass-filters

3.3 Development of Butterworth-low-pass filters in general

3.4 Designing a Butterworth low-pass filter of 6th order

3.4.1 Measurement results

4. Digitising and preparation of the signal

4.1 Sampling

4.2 Quantization

4.3 Coding

4.4 Requirements for digitising ELF-signals

4.4.1 Anti-aliasing filter

4.4.2 Sample frequency

4.4.3 Resolution

4.5 Microcontroller and adapting circuits

4.5.1 Sigma-Delta-ADC

5. Data exchange

5.1 The SPI-Bus in general

5.2 Initialization of SPI with the MSP430F2013 microcontroller

6. USB-Interface

6.1 Requirements to transfer the data into the compute

6.2 The IO-Warrior56 (IOW56)

6.2.1 Normal mode function

6.2.2 Special mode function

7. Interaction

8. Power supply

9. Software

10. Appendix

10.1 Circuit diagram

10.2 Board, layout and bill of material

10.3 Used formulaic symbols

10.4 Used equipment

10.5 List of sources

Objectives and Scope

The primary objective of this thesis is the design and development of a low-power signal acquisition device capable of detecting and digitizing weak signals within the Extremely Low Frequency (ELF) range (below 25 Hz) for subsequent analysis on a standard personal computer.

• Design of an analog low-pass filter to suppress noise and 50 Hz power hum.
• Implementation of signal digitization using the MSP430F2013 microcontroller.
• Integration of a USB interface for data transmission using the IO-Warrior56 chip.
• Optimization of the power supply and hardware layout for compact field use.
• Development of Windows-based software for data acquisition and display.

Excerpt from the Book

Summary of Chapters

1. Assignment: Defines the core objective of developing an acquisition device for signals below 25 Hz.

2. Concepts: Discusses digitization methods, comparing standard PC sound cards with dedicated external A/D converters.

3. Low-pass-filter: Explains the necessity of analog filtering and the design of a 6th-order Butterworth filter to minimize power supply hum.

4. Digitising and preparation of the signal: Details the sampling, quantization, and coding processes, and the specific implementation of the Sigma-Delta-ADC.

5. Data exchange: Describes the SPI bus protocol and its implementation on the MSP430F2013 microcontroller.

6. USB-Interface: Details the hardware requirements and the integration of the IO-Warrior56 chip for USB communication.

7. Interaction: Covers the timing and synchronization of data transfers between the microcontroller and the USB interface.

8. Power supply: Discusses the power requirements of the circuit and the use of DC/DC converters to support the hardware components.

9. Windows-Software: Explains the development of the Windows application using VB.NET to interface with the hardware via USB.

10. Appendix: Provides technical documentation, including circuit diagrams, PCB layouts, and a full bill of materials.

Keywords

Signal Acquisition, Extremely Low Frequency, ELF, Butterworth Filter, MSP430F2013, Sigma-Delta-ADC, USB Interface, IO-Warrior56, SPI Bus, Data Logging, Digitization, Sampling, Quantization, Analog Electronics, Microcontroller

Frequently Asked Questions

What is the primary goal of this diploma thesis?

The goal is to develop a low-power, cost-effective device for acquiring and digitizing extremely weak signals with frequencies below 25 Hz for analysis on a PC.

Which frequency range is targeted by this device?

The target range is the Extremely Low Frequency (ELF) spectrum, specifically frequencies between 0 Hz and 25 Hz.

Why is an analog low-pass filter required?

An analog filter is necessary to suppress 50 Hz power line hum, which would otherwise dominate the dynamic range of the A/D converter.

Which microcontroller is used for the digitization process?

The project utilizes the Texas Instruments MSP430F2013, which includes a 16-bit Sigma-Delta analog-to-digital converter.

How is the data transferred to the personal computer?

Data transmission is handled via a USB interface using the IO-Warrior56 chip, which acts as a generic USB-to-I/O controller.

What are the key technical challenges addressed?

The work focuses on maintaining a high signal-to-noise ratio, ensuring precise timing for sampling, and managing the conversion of raw bits into usable 16-bit integers via software.

Why was the Butterworth-type filter selected?

The Butterworth filter was chosen as a compromise, providing high steepness without introducing significant errors in the passband, unlike the Chebychev-type filter.

Can this system operate as a standalone data logger?

While the current design is optimized for real-time PC connection, the text notes that the use of a microcontroller allows for potential future extension as a standalone data logger with flash memory.