Copyright: Copyright ©1997 Marcel Veldhuijzen


Contents

BIP Electronics Lab Oscilloscope - 3.0

BIP FreeWare Fun - Wellerlooi, The Netherlands

bikkel@via.nl

http://www.via.nl/users/bikkel

Getting Started

How to set up the software?

How to set up the hardware?

Oscilloscope Controls

TIME/DIV.

CALIB. [%]

TRIGGER

VOLT/DIV.

CALIB. 0 V

Input Sampling

SAMPLING RATE

SAMPLING DURATION

Screen Controls

BRIGHTNESS

FOCUS

HORIZ. SHIFT

VERT. SHIFT

Advanced Topics

Calibrating the oscilloscope

Configuration file layout

The BIP Oscilloscope is a member of the BIP Labs 3.0 series which includes a spectrum analyzer, a frequency counter, a function generator, a noise generator and more to come. All BIP Electronics Lab software make use of standard PC hardware (already in the PC) and are free of charge available through the Internet.

The BIP Oscilloscope uses the sound card's input to measure signals. This means that the quality of the scope depends on the quality of your sound card. The scope has the following properties:

Sampling frequency:

The scope automatically uses the highest sample frequency available at the input that you select (usually maximal 44 kHz but people with 11 kHz max. also use the scope without any problems). According to somebody named Nyquist you can only accurately measure signals that have at most a frequency of half the sampling frequency.

Input impedance:

The same as the input impedance of your sound card. Some users of the oscilloscope use a 470 kilo ohm resistor that they place in cascade with the input to get a higher input impedance. Others fool around with combinates of potmeters and capacitors. Feel free to experiment a bit!

Accuracy:

The scope uses 8-bit samples to read the input signal. It does not make sense to compare the scope with commercially available products with better specs. BIP Labs Software is meant for the amateur that wants to experiment a little with an oscilloscope before buying a real one.


How to set up the software

Install the software in a separate directory. This directory should at least contain the executable file scope.exe and this help file scope.hlp. After you have started the software you should also see a file scope.cfg in the installation directory.

To uninstall the software simpy delete all files from the scope's directory. The scope does not make use of files in the windows- or other system directories, nor from the Registry Database of 32-bits operating systems.

When you start the scope for the first time you will get the chance to pick an input channel of your sound card. To change the different input channel select Input Channel from the Options menu.


How to set up the hardware

Create a home made measuring cable that fits in the input of your sound card that you wish to use as measuring input. Use a shielded, mono cable and connect the signal that you want to measure directly to this cable.

If you wish to measure higher voltage signals you may also need a voltage divider by adding a mono potmeter (100 kilo ohm linear for instance, or whatever you have lying around in your home electronics lab) to the input. You may also like to experiment by placing a resister of 100 kilo ohms or more in cascade with the input signal. This increases the input impedance of your scope.


TIME/DIV.

Use the TIME/DIV knob to adjust the time base of the oscilloscope. When the knob shows, for instance, 5ms then this means that every division on the scope screen extends (in the horizontal direction) a period of 5 milli seconds.

The scale of the time base is either specified in milli seconds (1 ms push button down) or specified in micro seconds (100 micro seconds push button down). In the latter case every value of the knob should be multiplied by 100 to get the value in micro seconds: for instance knob position 5 means 500 micro seconds.


BRIGHTNESS
Use the Brightness knob to adjust the brightness of the signal on the oscilloscope screen. Only the sigal can be adjusted, the grid remains the same. Depending on your graphics card, the brightness knob allows you to switch from dark green to very light green to pure white.


FOCUS
Use the Focus knob to adjust the focus of the signal. In the digital oscilloscope the focus means the line thickness of the signal. The minimum line thickness is 1 pixel.


HORIZ. SHIFT
Use this knob to shift the sample to the left or the right. Also when the oscilloscope is in stop mode (not sampling the input signal) you can still shift the signal horizontally.

If you wish to increase the horizontal length of the sample you should increase the sampling duration.


CALIB. [%]

With the CALIB knob you can fine tune your calibration in the vertical direction. This will change the vertical sensitivity. When you wish to (accurately) read the voltage of your input signal you must place this knob in the middle position (0%). Use the calibration dialog to pre-tune the oscilloscope.


Calibrating the oscilloscope

Calibrating the oscilloscope is only necessary in the vertical direction (voltage axis). There is no need to calibrate the horizontal time axis. This means that, in every case, frequency measurements are very accurate.

Choose Options, Calibrate to display the calibration dialog.

The calibration dialog has two controls that you use to calibrate the oscilloscope. In order to start calibration first connect a well known signal to the input of the oscilloscope, for instance a 50Hz or 60Hz sine wave from a transformer. The top-top voltage of this signal should be known. The frequency of the signal should be in the neighborhood of the frequency of signals that you usually measure (so for instance preferably 1kHz if you measure sound signals).

Create a sample of your input signal on the oscilloscope's screen. Use the Coarse and Fine tuning controls on the calibration dialog to adjust the picture (you will need to press Apply several times). During calibration it is also allowed to change any (other than the CALIB[%] knob) oscilloscope control. This will not harm the calibration in any way. When the picture on the scope's screen has the same top-top value as your input signal then you are ready.

Tip: you may choose to Stop the oscilloscope while calibrating. This gives you one steady sample to calibrate.


TRIGGER

The Trigger knob sets the trigger level from 0 to 255. Every digital sample of the oscilloscope ranges from 0 to 255 (8-bits sample). Enabling triggering allows you to monitor a signals frequency more accurately since a period of the signal will always start at the same position on the horizontal time axis.

Note that the push button Off must be up to enable triggering.

Tip: when you don't see a signal on the screen try to turn triggering off (pushing the Off button). Noisy signals (signals with a lot of varying frequencies) can not be triggered by the oscilloscope.


VOLT/DIV.

To zoom in on the vertical level use the Volt/div. knob. After you have calibrated the oscilloscope you can change the number of volts that every vertical division stands for. Note that you can also use this knob when you have stopped the signal.


CALIB. 0 V

Use this knob to calibrate the zero volt position of the oscilloscope. You can perform a zero volt calibration by short circuiting the input and then turning the Calib 0V knob until the green input signal line matches the yellow zero volt line.

Press the Store button to strore the change. Note that pressing the Store button will also store all other control settings. Also take into account that settings will be stored automatically when you close the oscilloscope program.


SAMPLING RATE
The Sampling rate knob specifies the period of time in milli seconds that the scope will monitor the input signal. A value of 1000 for instance means that every second (1000 milli seconds) the input will be sampled.


SAMPLING DURATION
The Sampling Duratation is the time that the oscilloscope keeps monitoring the input signal. A sampling duration of 500 milli seconds means that the input signal is being monitored (without interuption) for a period of time of 0.5 seconds.

Note that using the sampling controls you can create odd behavior like monitoring a signal for 1 second every 0.5 seconds. In this case the signal is actually monitored continuously (without interuption).


VERT. SHIFT
Use this knob to shift the sample up or down. Also when the oscilloscope is in stop mode (not sampling the input signal) you can still shift the signal vertically.


Configuration file layout

The Oscilloscope uses a configuration file scope.cfg, located in the same directory as the executable. The following shows a sample configuration file together with some comments. If you have changed something in this file and the oscilloscope does not work anymore then simply delete the scope.cfg file. The Oscilloscope will automatically create a new default configuration file.

[GeluidsBlaffer]

Nummer=0	// The device number that you use as input channel.

[Calibration]

Volt255=391	// Value of calibration (set by Options, Calibrate).

Offset=3	// Offset of zero line relative to the yellow line.

[Opties]

TekenNullijn=1	// 1 if you wish to see the yellow zero line.

TekenGridBijSave=1	// 1 if the grid is drawn by save and clipboard copy.

[KnopPosities]	// Positions of all the scope knob controls.

Tijdbasis=3

Calibration=0

Trigger=131

VoltPerDiv=4

CalibNul=3

Focus=0

HorzShift=-34

VertShift=0

SamplingRate=532

SamplingDuration=470

[Buttons]	// Positions of the push buttons of time base and trigger.

MicroSecs=0

TriggerOff=1


Input Channel

Choose Options, Input Channel to open the Input Channel dialog.

Select the sound card input of your choice that will be used as the input of the scope. If no sound cards are listed then you can not use the oscilloscope on your PC.