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Low-cost Virtual Logic Analyzer (LVLA)


Low-cost Virtual Logic Analyzer (LVLA)

by

Lim Bee Nee, Student

Tan Chee Hao, Student

Rodney Tan, Advisor

UCSI University

Malaysia

Products Used:

1.      NI USB-6008 DAQ

2.      National Instrument LabVIEW 8.5

The Challenge:

The Low-cost Virtual Logic Analyzer (LVLA) is a device for digital triggering display. The challenges are time and cost. Designed for academic usage, the virtual logic analyzer is developed base on low-cost feature so that every student can possess it. The LVLA has 8 channels and maximized functions.

The Solution:

The NI USB-6008 DAQ acquire digital input through miniature hooked test probes, where signals obtained are loaded into the LVLA virtual instrument for analysis and displaying on screen. Developed with LabVIEW 8.5, it simplifies the monitoring of digital signals and features the portable, user-friendly, and inexpensive advantages.

Abstract

The LVLA is discussed by first introducing why it is needed, what its advantages are, and who it is targeted to. The system overview sub-section gives a complete picture of how the system with NI USB-6008 DAQ and LabVIEW 8.5 is communicated and utilized. The connections and tools used are presented through block diagram. Following is the results and discussion sub-section, which will show the screen capture of the LVLA virtual instrument front panel, the hardware setup, as well as detailed discussion on the results obtained. Lastly, the conclusion sub-section will conclude the whole project.

Introduction

A logic analyzer is an electronic instrument that functions as multi-channel version of a digital oscilloscope, which presents signals in a digital circuit so that user can easily perform circuit checking and detect any errors. It recognizes two logic levels: 0(LOW) and 1(HIGH). An oscilloscope can be used as logic analyzer too, but it


normally has only two channels and is usually not sufficient for students to perform more than 2 signals checking at one time. Thus, logic analyzer is needed when a more complex triggering is wanted to be observed and when more channels are required.

With the expensive market price of logic analyzer ranging from RM 5k to RM 20k, the virtual logic analyzer is appropriate to be developed. The LVLA is made up by NI USB-6008 DAQ and LabVIEW 8.5, thus featuring the key identities of portable, Universal Serial Bus (USB) powered, inexpensive, user-friendly and powerful virtual instrument. Mainly targeted for student learning and academic usage, the LVLA is built to have 8 channels of test probes. The acquired signals are then transmitted between the NI USB-6008 DAQ and the LabVIEW 8.5 for data analyzing. It illustrates the digital signal on immediate time interval as of how the components or devices obtained the signals. The LVLA virtual instrument allows user to monitor and understand digital signals through waveform chart, as well as capture and save digital waveform instantaneously.

As its name LVLA suggests, the set of miniature hooked probes on a multi-coloured cable create a low-cost probe solution, which is an added advantage for this virtual instrument. The 8 channels of test probes are expected to meet the requirement and enough to support especially the usage of Year 1 and Year 2 tertiary level students.

System Overview

The complete system overview of Low-cost Virtual Logic Analyzer (LVLA) virtual instrument is shown with block diagram in Figure 1.

BLAH.jpg

Figure 1. LVLA System Overview Block Diagram

The system shown consists of 8 channels miniature hooked test probes connected with ribbon cable and IDC connector, NI USB-6008 DAQ unit, and the notebook installed with LabVIEW 8.5 LVLA virtual instrument. The LVLA reflects a very simple yet useful virtual instrument. Aside from the LabVIEW 8.5 and NI USB-6008 DAQ, it requires only the test probes to obtain the digital input from any components or devices that undergo digital signals. The miniature hooked test probes enable users to reach and hook the probes onto any tiny little wires on bread board, through hole soldering devices on circuit board, and even surface mount devices. The acquired signals are thus sent


through the digital input port P0 on the NI USB-6008 DAQ, analyzed and then displayed in waveform chart on the front panel of the LVLA virtual instrument.

Results and Discussion

The user interface of the LVLA virtual instrument in LabVIEW 8.5 is shown in Figure 2 below.


BLAH.jpg

Figure 2. LVLA Virtual Instrument User Interface


The user interface of the LVLA virtual instrument consists of a waveform chart, amplitude display column, time knob, capture button, and stop button. The waveform chart is used to display the digital signal. There will be 8 lines of digital signal waveform acquired from each test probes running continuously and simultaneously on the display screen, representing the 8 channels. The colours of the lines are similar to the colours of the ribbon cable connected to the test probes. The amplitude display column indicates the level of the waveform whether it is high or low. The time knob is used to change the time of the waveform display. For the LVLA, the time delay is set at 0.001 s. Thus, when the time knob is positioned at 0, it will use the default time delay value of 0.001 s; whereas, if the time knob is pointing at value of 10, it will be 0.01 s of time delay between every interval of time. The capture button is to capture the waveform displayed and save it as JPEG image format at immediate time when the button is pressed; while the stop button is to stop the data analysis process of the LabVIEW 8.5 virtual instrument upon pressed.

A logic analyzer is essentially used for capturing digital data in system that requires too many channels to be examined with a 2 channels oscilloscope. Oscilloscope is mostly used for analog measurements, where small voltage changes and time interval measurements are very crucial; whereas for logic analyzer, it is widely used to observe digital signals of 0 and 1, and is usually applied when timing analysis is not that critical.

For the hardware set up of LVLA, the digital test bench serves as testing purposes. The test probes can actually be connected to test on any other sources or components that undergo digital signals. The LVLA can also be used as diagnostic tool to observe the digital signals of any components, devices and appliances.

Figure 3 shown a digital test bench is set up with using microcontroller unit to produce digital waveform. The waveform is acquired by test probes and observed on screen. The digital signals displayed are exactly equal to the digital waveform running in the test bench. The complete system setup of the LVLA is shown in Figure 3.

BLAH.jpg

Figure 3. LVLA Virtual Instrument Experiment Setup

The LVLA is tested and proven to be able to acquire and display the digital signal waveform up to 10 Hz frequency. If the experiment is not on timing critical analysis, the digital input can be acquired up to 1 kHz. However, these are not the limitations of the LVLA. The LVLA built using the LabVIEW 8.5 is suitable to be used for any other frequencies as the software is competent for any usage. Thus, it is budget-based limitation, where different DAQ card will have different sampling rate. The NI USB-6008 DAQ has sampling rate of 10 kS/s, which is sufficient for academic usage; whereas if digital input with frequencies higher than 1 kHz has to be analyzed, a higher speed DAQ card can be adopted, such as NI USB-6009 DAQ with sampling rate of 48 kS/s. At the same time, the low-cost feature is achieved as the raw materials such as the test probes and connector cost approximately RM 9 only.

Conclusion


The LVLA virtual instrument is designed to function as low-cost 8 channels logic analyzer, mainly to support student learning and academic usage. It can also be used as a diagnostic tool to observe the waveform of a circuit board. Thus, both the NI USB-6008 DAQ and LabVIEW 8.5 are successfully utilized in the LVLA project.

For more information, contact:

Rodney Tan Hean Gay

Deputy Head of Embedded System Research Group (ESRG)

Senior Lecturer

UCSI University, Malaysia

No 1, Jalan Menara Gading, UCSI Heights, 56000 Kuala Lumpur Malaysia

Tel: +6017-3078955

Fax: +603-91023606

Email: rodneyt@ucsi.edu.my

Comments
carln
NI Employee (retired)
on

Very nice!  Do you have the VI to share?

el1nicoangell
Member
Member
on

Saludos amigo, esta demasiado bueno este aporte.. Yo tengo una 6008 y he realizado varios montajes en la universidad y este supera cualquiera de ellos... Seria de muchisima ayuda que bajaras el VI para utilizarlo con la mia y compartirlo con otros estudiantes de mi facultad.   De antemano muchas gracias.

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