Lab-in-a-Box

The Lab-in-a-Box is an introductory electrical engineering project kit and accompanying textbook used for ECE 2074 Electric Circuit Analysis Laboratory and ECE 3074 AC Circuit Analysis Laboratory. It includes a breadboard called the A&D or "ANDY" board.

ANDY Board

The ANDY board has ±9V and +5V sources, clock signal, sine/square wave signal generator, 16 dipswitches, 16 LEDs, and two pushbutton switches. The dipswitches and LEDs are used for digital applications in ECE 2504 Introduction to Computer Engineering. The signal generator is for RC circuits in the ECE 2074.

A&D User Manual & Test Procedure v2.2

Parts Kit

The parts included with the kit include resistors, capacitors, inductors, light emitting diodes, and a handful of integrated circuits including operational amplifiers, and digital logic chips.

Software Oscilloscope

Attenuator Circuit

The attenuator circuit in the Lab-in-a-Box manual is setup for the gain of the Behringer UCA202 on Windows XP. You can either work with your teaching assistant to develop an attenuator circuit that fully compensates for the gain of your system in hardware or use the software tweaks to xoscope described below. File:Lab-in-a-Box attenuator circuit.png

The ECE: Lab-in-a-Box Tutorials page has an article Experiment 12: Calibrating A Sound Card Oscilloscope. A schematic to be built on the ANDY board is on page 3. The tutorial uses the Zeitnitz windows oscilloscope software.

Software

While xoscope or the Lab-in-a-Box attenuator circuit could use some tweaking to work out of the box together, xoscope can be readily modified to display scaled maximum, minimum and peak-to-peak values. The first step is to obtain the program source code. On a Debian-based systems like Ubuntu, just run sudo apt-get source xoscope.

Once the source has been downloaded and unpacked, edit sc_linux.c to use /dev/dsp1 rather than /dev/dsp:

sed -ir 's%(#define SOUNDDEVICE "/dev/dsp)(")%\11\2%'

Next, modify the display code in display.c to display a scaled value. Around line 186, change the code to read something like the snippet below. Use your multimeter to measure the the RMS voltage, calculate the peak-to-peak that should be displayed and tweak the divisor, re-compile and re-run until the value is correct.

    else
        sprintf(string, " Max:%f - Min:%f = %f Pk-Pk ",
                (float)stats.max / 3.2, (float)stats.min / 3.2,
                ((float)stats.max - (float)stats.min) / 3.2 );
    gtk_label_set_text(GTK_LABEL(LU("min_max_label")), string);

To compile the modified source, simply run make. To run the newly compiled binary, run ./xoscope. Refer to the xoscope article for instructions on using the scope.

External Links

• VT news story
• CEL listing of the lab kit