DrDAQ: It turns your PC into a science lab
DR WHO? Yes, it is an unusual name. But DrDAQ is just one of a whole host of data acquisition devices currently available from the respected UK company Pico Technology.
Pico Technology has been manufacturing PC-based (hence “virtual”) instruments for data acquisition since 1991. PC-based test and data acquisition equipment is quickly emerging as the most cost- effective approach to high quality instrumentation. DrDAQ is a perfect case in point. Here’s why.
Generally, data loggers provide a means of making and storing real- world measurements over a period of time. With the right type of transducer (or sensor), any kind of physical quantity can be measured – temperature, pressure, radiation, acceleration, etc.
Having made and stored (logged) the measurements, we must then be able to display them in an easily understandable way. This means charting and graphing the data, and perhaps performing mathematical manipulations as well.
Actually, the term “data logger” describes only part of what DrDAQ can do. For example, it can also display measurements in real time on an oscilloscope-like display.
The package consists of both hardware and software components. Lets look at the hardware first.
|Table 1: Input Channel Specification|
|Sound waveform||±100||0.2||Not calibrated|
|Sound level||55 to 100dBA||1dBA||5dBA|
|Voltage||0 to 5V||5mV||3% of FSD|
|Resistance||0 to 1MW||0.1kW (at 10KW)||2% (at 100K)|
|Temperature||0 to 70°C||0.1°C (at 25°C)||2°C (at 25°C)|
|Light||0 to 100||0.1||Not Calibrated|
|Table 2: External Sensor Specification|
|pH||0 to 14||0.02pH||Calibration dependent|
|Temperature||-10 to 105°C||0.1°C (at 25°C)||0.3°C (at 25°C)|
The hardware consists of a single PC board measuring just 55 x 70mm. It plugs into the parallel (printer) port of your PC via a 2-metre cable and requires no external power. A thick foam-like pad glued to the rear of the PC board protects the majority of the workings from physical damage, as it’s not enclosed in a case. We’ll see why in a moment.
Included on the board are nine analog inputs and two digital outputs. Four of these inputs are connected to sensors located right on the board! Sound, light and temperature sensors enable you to begin experimenting immediately.
Also included are connectors for two additional external temperature sensors (or user-defined sensors) and a standard-type pH probe. External sensors can be purchased from Pico Technology as required.
A screw-type terminal block provides connection for the remaining two inputs, one measuring voltage and the other resistance. Access to one of the two digital outputs is also provided on the terminal block, with the other driving an on-board LED. Tables 1 & 2 show the analog input and sensor specifications.
|Fig.2 (left): multiple channels can be simultaneously. Just add them in here and hit the edit button to configure.|
|Fig.1: all settings are accessible from the main Recorder window and the large buttons on the toolbar provide quick access to often used functions.|
Our preview copy of DrDAQ software was supplied on three floppy disks but the full release (available as we write) will be supplied on CD-ROM. It runs on Windows 3.1x, 95, 98, NT and 2000.
No particular hardware requirements are listed, although you will need a free parallel port for connection to the DrDAQ hardware. If you only have a single parallel port and it’s already in use, you can either purchase an add-on parallel port card or a switch box – or switch cables manually if you have more patience than I do!
As with most Windows software these days, installation is a breeze. You simply launch the setup program and follow the on-screen prompts. The software is divided into two distinct modules, defining the two major functions of this package. PicoLog provides the data logging functionality and PicoScope the real time display.
PicoLog consists of a recorder for sampling and storing data and a player to display the results. Although the player software is integrated in the recorder, a separate player is also included, which means that you can view previous recordings while another is in progress.
Before logging can begin, PicoLog’s recorder needs to know where to store the data as it’s measured, as well as which inputs to sample, how often they should be sampled and how many samples to make.
Other parameters such as scaling and units of measure are also important, as the player will use these when graphing the results. Let’s briefly look at the available settings.
|Fig.3: PicoLog completes most settings for you if measuring a known sensor. If you get stuck, the Help button is always handy.||Fig.4: the Edit button in Fig. 3 brings us here and this is about as tricky as it gets. This is where we define what is needed to make the output from the player (the graphs) look right!|
|Fig.5: setting the sampling rate, and hence the number of points that will eventually be plotted on the graph.||Fig.6: results of our tests from PicoLog graph. Don`t be fooled by our rather comprehensive view - graphs can be much larger than this if need be. Note the scrolling and zooming buttons on the right ride of the Window.|
All settings are accessed from the main menu (see Fig.1) and can be saved in a unique file for later recall. For our tests, we decided to monitor the sound, temperature, light and pH sensors (see Fig.2). As you can see, the digital outputs are also configured here, with options of “always on”, “on when recording”, “on when alarm” or “off when alarm”.
Highlighting any of the measurements and hitting the Edit button brings up scaling, measurement (AC, DC or frequency, depending on the selected sensor) and scan time options (see Fig.3). If measuring the DrDAQ sensors, PicoLog configures most of these settings for you.
For cases where you’re measuring custom sensors, PicoLog provides additional options for setting units of measure, scaling and numbering (see Fig.4). It’s even possible to read scaling values from an external file for non-linear measurements!
Also of interest here is the alarm feature. This sounds an alarm (the PC speaker “beeps”) when any of the measurements are outside predefined upper and lower limits (as defined by the user). If enabled, alarm conditions can toggle the digital output lines, too (see above).
The rate of measurement (sampling interval) and the total number of measurements to be made are configurable from the main settings menu (see Fig.5). Intervals from milliseconds to hours are programmable, with a maximum of one million samples!
We’ve tried not to bore you with detailed explanations of every setting here, as the on-line help is indeed helpful and Pico Technology have included a “Guided Tour” to ease you into the driver’s seat. Even better, you can test drive a working demo off the DrDAQ website – but more on that later.
Once setup is complete, it’s just a matter of clicking on the “record” button on the main menu to start record- ing. You can keep an eye on what is happening during recording by enabling the “monitor” setting for channels of interest (see Fig.1).
Displaying the results of a recording is very straightforward. Simply launch the PicoLog Player, load the recorded data file from the main menu and hit either the “graph” (Fig.6) or “spreadsheet” (Fig.7) buttons.
|Fig.7 this is what the Spreadsheet output looks like. Logged data can be saved in a text file or pasted directly into other applications.|
Graph displays can be scrolled up and down, magnified or reduced and printed at will. The entire image (minus the ugly frame) can be copied to the Windows clipboard and pasted into any popular application.
The spreadsheet mode provides a nice tabulated display of the recording. It also allows the data to be saved in standard text format – a must for advanced users who wish to do further processing in other applications.
|Fig.8: displaying inputs in real time. Three different views are shown here using six windows. In the bottom right corner, three meter views show the temperature from the on-board sensor, as well as voltage and resistance measurements from inputs on the terminal block. The Scope view above these shows the output from the light sensor : in this case, the 100Hz flicker of our office fluorescent lighting. The Spectrum window at bottom left is also displaying the light sensor output, with the window above that displaying the sound (microphone) sensor output.|
A real bonus with this package is its ability to display measurements in real time. This feature (called PicoScope) is often only available on more expensive virtual instruments and despite the relatively low sampling rate of the DrDAQ hardware (10kS/s), it could still be a very useful instructional tool.
Samples can be displayed in a variety of different ways, called “views”
(see Fig.8). To summarise, these are:
(1) Scope view: samples are displayed in an oscilloscope-like format (amplitude versus time). The horizontal timebase can be set up just like a regular ’scope, with a 10 x 10 grid and selectable intervals of 1ms to 50s per division. Alternatively, you can set the timebase in terms of time per complete sweep if preferred.
The vertical axis displays amplitude in millivolts. The scaling can be easily customised, allowing direct display in any units you desire. For example, if measuring a pressure sensor, the vertical axis could be marked in kPa.The sampled data can be displayed in a number of different formats. These are:
As well, more than 20 calculated measurements can be performed on either the whole waveform or part of the waveform (selected with moveable cursors). The results are displayed at the foot of the waveform. Some examples of calculated measurements are frequency, high pulse width, low pulse width, duty cycle, rise time, etc.
Also of note is the chart recorder mode, which is automatically assumed when the sampling rate is longer than one second. This mode is perfect for slow changing inputs such as those from temperature sensors.
(2) Spectrum view: samples are displayed in spectrum analyser format (amplitude versus frequency). Mathematical calculations (called FFTs) are used to convert sets of samples taken at fixed time intervals into a distribution showing the amount of energy in a range of frequency bands.
For this view, the Y-axis represents power and can be set to either volts RMS or decibels. The X-axis represents frequency, displayable in either linear or logarithmic format.
We did notice that our mouse froze for a brief moment each time a spectrum window was updated (presumably because of the complex calculations involved), so watch out for this if you intend running multiple spectrum windows on a slowish PC.
(3) XY Scope view: in this view, samples from one channel are plotted against samples from another. This means that both the X and Y-axes represent amplitude (in millivolts).
|The DrDAQ hardware with PC parallel port cable and two external sensors connected. The black object between the white and grey connectors is a tiny electret microphone. The light sensor is the tiny round object to the left of the black screw-terminal block. Immediately to the left of the light sensor is a glass-encapsulated thermistor which is used for tempertaure sensing|
(4) Meter view: as the name suggests, this view displays the desired channel in a digital, meter-like format, com- plete with bargraph. AC, DC or frequency measurements are possible. Meter views “know” about DrDAQ sensors and will, for example, display temperature sensor inputs directly in °C.
(5) Composite view: a copy of up to four active views can be displayed in a single composite view. A variety of formats such as side-by-side and overlay are supported. This is useful for printing multiple views on a single page, or performing before and after waveform comparisons.
Any analog input (channel) can be displayed in its own scope, spectrum or meter window. In addition, multiple views of the same channel are supported, so you can, for example, display a channel in both a scope and meter view simultaneously.
Samples can be displayed either continuously or after a particular condition occurs. This is called “triggering” and is indispensable for viewing random or intermittent events. Any channel can be selected as the trigger source. Triggering can be set to occur at a particular input signal level (threshold), either rising or falling.
Even better, you don’t have to remain glued to the display waiting for that intermittent event because PicoScope can automatically save the sam- ples to disk when the trigger occurs. Samples are stored in sequentially numbered files for easy recovery and viewing or printing, just like live waveforms.
Pico Technology has developed DrDAQ primarily for the education market and it shows. As well as PicoLog and PicoScope, the software CD includes a whole host of interesting science experiments that can be performed using DrDAQ.
|Another view of DrDAQ. The “brains” of the unit consists of surface-mount components which are hidden on the back of the board.|
The experiments are grouped into categories such as Biology, Chemistry, Physics and General Science. Experiments include both teacher and student versions. Here are some examples from the physics and chemistry sections:
The DrDAQ web site is continually updated with new experiments as they become available and includes many ideas for experiments of your own. Check it out at drdag.html!
The DrDAQ product comes with free lifetime technical support, free software updates from their website and a 2-year return-to-manufacturer warranty on the hardware.
You can also try before you buy with free demo software (complete with simulated data) from http://drdag.html/download.html
Are you already familiar with data loggers and have a specific application in mind? Write your own software using DrDAQs DLL drivers for Windows. Examples in C, Delphi and Visual Basic are included! Once again, these are free to download from the DrDAQ website.
DrDAQ is available in Australia from Emona Instruments. Check out their website at www.emona.com.au or phone (02) 9519 3933.
(This article was first published in the Australian electronics magazine SILICON CHIP, July 2000. Pico Technology would like to thank the magazine for permission to re-print the article.)