Back in the early days of the personal computer revolution, TV and radio interviewers used to ask, 'What's it all for?' One of the standard answers was, 'Well, we can run our central heating with it'. Overall, it's likely the answer was designed to be understandable to the non-technical, media-oriented audience - I doubt that many people actually used their prototype machines to control their central heating, and those that did probably froze to death the following year. Over the years, personal computers got better and cheaper and took up more sensible jobs such as pretending to be a typewriter or a simple calculator. However, some people were still of the opinion that they could do more. Clearly, the people at Pico were among them because they built DrDAQ.

A PC can be programmed to make measurements, analyse them and act on them. The problem is that a standard PC has very few 'feelers' to the outside world - keyboard, mouse, that's about it. The traditional solution is to add an analog-to-digital (AtoD) converter. These tend to be expensive, and you usually have to open your PC to add them. Even when you have an AtoD converter installed, your troubles aren't over because you need sensors, which are expensive and tricky. All in all, if you have ever considered using a PC to make automatic measurements of anything, you have probably given up due to cost and complexity.

Something that seems so simple in theory soon becomes impractical when you look into it. This is where DrDAQ enters and changes everything. DrDAQ is a low-cost AtoD converter with a range of sensors built in. It is easy to install because it just plugs into a parallel port, and it comes with all the software you need to get started. If you do need external sensors, you will find that adding them is made as easy as possible. There is even a limited output facility that you can use to control things.
 

Control call

What could you use DrDAQ for? Well, if you have ever considered a PC-based instrumentation project, you are probably reviving your old ideas already. If not, all you have to do is think about something you would like to measure or monitor on a long-term basis. The most obvious application is in education. Take a PC, a portable if you like; add a DrDAQ, and you have a computer-based lab. The good news is that the PC doesn't even have to be a particularly good one. An almost-scrap PC running Windows 3.x can be used, because DrDAQ comes with Win16 and Win32 versions of the software. Using DrDAQ, you can automate many chemistry, physics and biology experiments and, in doing so, you can learn a lot about the instrumentation side of using a computer. Equally, a class demonstration with the help of a DrDAQ-equipped PC is likely to be more informative, having the ability to present graphs of what is going on in real time.

When you move away from educational applications, you will find that not every idea is suitable for a DrDAQ setup. This is mainly because instrumentation applications quickly become demanding in terms of the number of measurements per second, and the quality and robustness of the sensors. For example, you might decide to use DrDAQ to instrument the engine of your classic car, one that doesn't already have a computer under the bonnet. In this case you would be able to use DrDAQ, but the problem would be in buying or constructing suitable sensors for carbon monoxide, RPM, oil pressure and so on. After solving these problems, the cost of DrDAQ would be such a small part of the entire project you'd probably settle on something more sophisticated.

DrDAQ is good at the smaller, quick-to-lash-up-and-throw-away type of problem. If you wanted to know the temperature range or the number of hours of sunlight in a particular spot in your garden or greenhouse, DrDAQ would provide a quick and easy solution.

DrDAQ is a neat printed circuit board that is supplied without a case. The electronics are on the back of the board; only the connectors and built-in sensors are found on the front. The back is protected by a foam rubber sticker. If you plan to use DrDAQ in a permanent installation, putting it in a box would be a good idea. As far as connecting it to the PC goes, a standard parallel port is all that is required. It doesn't have to be a bi-directional port - any parallel port will do. A 25-pin D-type connector is used, and a printer cable is supplied to connect DrDAQ to your PC. The only possible problem is if your PC has a printer connected to its parallel port. DrDAQ doesn't share a parallel port at all well. If it is necessary, installing a second parallel port isn't expensive. You can't use a USB-provided parallel port for DrDAQ, although one could be used for the printer to free up the existing parallel port.
 

Sense and sensors built in

The unit comes with a microphone, a light sensor and a temperature sensor built in and ready for measuring. A four-way screw terminal connector provides additional inputs for voltage and resistance measurements and a single digital output. The digital output is a simple on/off output that works between 0V and 5V (for example, with TTL). However, it is important to note that it can only supply 1mA, so it needs an amplifier or relay to control anything in the outside world. A small LED on the PCB is the only other output. At the front of the board, two telephone-style connectors are used to connect general external sensors. At the moment, only temperature sensors are available but a humidity sensor will be available soon.

A BNC connector is also provided, so you can connect a pH sensor. If you don't know what pH is, you probably won't want to use one. Put simply, it measures acidity and alkalinity on a scale of 0 to 14, with a pH of 7 being neutral. If you want to make use of DrDAQ for chemistry or environmental measurements, a low-cost pH meter is a very attractive option. A pH sensor is available from Pico and costs £35. This means that a complete pH meter/data logging system can be bought for less than £100, which compares well with other pH meters with a similar resolution.

The entire range of sensors, and their resolution and accuracy, can be seen in the table on page 420. As you can see, it is reasonable for such a small, low-cost device. The final thing you need to know is that DrDAQ can sample 15,000 readings per second, or better, depending on the speed of the PC that accepts the data. Quite reasonable, but not fast enough for many applications. For example, you can use DrDAQ to sample sound waveforms but, with a sampling rate of 15KHz, the highest frequency you can work with is 8KHz. (As a rule, the highest frequency is always half the sampling rate.) So if you attempt to use DrDAQ for the digital input of speech or music, the quality would be greatly reduced. A standard sound card would do this a lot better than DrDAQ, anyway.

Installing DrDAQ is so simple as to require little comment - just plug it in and it works. The software is just as simple to install by using the floppy disks provided. These install a driver for the parallel port, two pieces of applications software and some programming examples.

The applications software is what really makes DrDAQ value for money - you can download demo versions from the Pico Web site. The star of the show is PicoScope, a software oscilloscope. This probably isn't the software you'll be using for serious applications - for that, you'll have to use PicoLog, a data logger, or write your own software. However, it will probably be PicoScope that you use to get started, and playing with it is great fun.
 

PicoScope

The first thing to say here is that PicoScope has all the outward appearances of being an oscilloscope, and it has the same basic function, but using it doesn't feel like using a real oscilloscope. Part of the reason is that the feedback time is much longer. If you sit in front of a real scope, you have almost instant feedback on the result of any adjustment you make; getting it to lock and trigger the way you want it to is a skill you learn by trial and error. I don't think you can learn the same skill by playing with PicoScope, but you can discover what the controls are all about.

When you start PicoScope, you will see something similar to an oscilloscope display. By default, the first channel is set to the sound sensor with time base and sensitivity set correctly, so if you whistle you will see a rough sine wave. How rough will depend on the quality of your whistle. This is a very good way of finding out how the PicoScope works.

PicoScope simulates a four-channel scope, and you can select any of the internal or external sensors to display on any channel using the drop-down lists. You can also change the time base by selecting from a drop-down list. You can set the trigger mode in the same way. The trigger determines when the trace starts. Without a trigger, even the simplest display on a real scope drifts and becomes difficult to see - with it, the display is stable and you can see what you're looking at. For one-off wave forms, you can capture transients by setting the trigger to start the trace at a particular point on the wave form. This works the same way in PicoScope, but you can also drag a small visual indicator that sets the trigger voltage - in other words, the voltage that the input has to reach before the trace starts. In addition, there is the facility to freeze a trace by clicking on the Stop button in the lower left-hand corner. Try this with a real oscilloscope and it won't work unless you have a very expensive storage scope.

Other improvements over a real oscilloscope include the ability to place horizontal and vertical lines on the screen to specify measurement points. The values of x and y at specific positions are displayed on the screen. You can also select measurements you wish to be displayed, such as AC voltage, maximum, minimum, frequency and mark space ratio. These can be based on the whole displayed wave form or just a specified portion placed between markers. The only problem was that if I selected the wrong scale, the program crashed. There is also a facility to set alarms, which can be used to make the PC go beep or stop the trace when the measured value goes out of the set range.
 

Spectrum gadget

In addition to the software oscilloscope, PicoScope has a software spectrum analyser built in. When you select View,New Spectrum a new window opens and displays a frequency plot. The analysis is performed for each scan of the oscilloscope, which effectively gives you a real-time spectrum of the signals being displayed. By default, the spectrum is computed for 256 frequencies from 0Hz (DC) to the maximum that you have selected (up to 5KHz). If you want a more accurate spectrum, you can select up to 4,096 but this takes more time and slows the display down. Similarly, you can open more than one oscilloscope and spectrum analyser, but this slows things down even more.

To give you some idea of how good DrDAQ is, place it under an incandescent (not fluorescent) light - you can see the 50Hz AC wave form. If you put this through the spectrum analyzer you will get a peak at 100Hz, and you can spend a few minutes working out why. What is even more surprising is that the same sensor can pick up the frame rate of a TV monitor. If you hold it up to the PC's display, you can see the brightness of the phosphor vary as the electron beam scans it. Use the spectrum analyzer to see how fast the monitor refreshes. If you want to record slowly varying data, a chart recorder is automatically selected when you set a time base running slower then 500ms per division. Finally, it is worth mentioning that you can open a standard voltage meter as a separate window. There is also an XY scope which allows you to do things like display Lissajous figures and phase plots.

You can save a configuration as a file or add it as a menu option. To add a menu, you have to define a .ini file - this gives the menu structure and the files to load if the menu option is selected, allowing you to customize DrDAQ to a number of standard tasks and select them from the menu as required.

What I found surprising about PicoScope was the range of features that weren't well documented, if they were documented at all. For example, you can save data to a disk file in text format or as a .wmf format vector drawing of the display. You can also set the trigger to save data to a file so that you can really capture transients. What isn't made very clear is that you can do this using the oscilloscope or the spectrum analyzer, so you can capture raw data or frequency distributions. Even less well documented is the fact that you can paste an active link using dynamic data exchange (DDE). DDE may be an old technology but it is still supported, and it provides a way of making an active link between an application such as a spreadsheet and the raw data or spectrum. There is a brief example of how to program the DDE link in Excel. Another example of poor documentation - you can define your own sensor characteristics. A signal conditioner file is used, but the documentation is missing. 
 

PicoLog

The second significant piece of software included with DrDAQ is PicoLog. In principle, data logging is easy: you say what data input you want to record, and how often. In practice, though, data logging software is often difficult to use. However, PicoLog is both easy and surprisingly powerful. I say 'surprisingly' because its user interface is small and looks unpromising. Its most powerful features are also well hidden. For example, it can be used to log data over a TCP/IP network. Simply start a copy running on one machine and set it as the server, and start a copy running on another machine as the client. Once both programs are running, the client displays the readings being made on the server.

Using the PLW Recorder is easy. Simply select the input channels you want to record and how often you want to record them. When you press the record button, a file is created storing the data as requested. You can re-record the data and view it using a spreadsheet-style window or a chart. The chart can represent data plotted against time or an XY plot. You can view the logged data on a chart.

You can include calculated parameters in the data logging, such as power from voltage and resistance. An alarm can be set on each channel. This can include a Holdoff parameter, which gives the amount of time the value can be outside of its specified range before the alarm is raised. If you want to record data automatically or at a remote site, PicoLog is as good a way of doing it as any.
 

Programming

The supplied software is useful for getting to know the hardware and for investigating how the data acquisition works, but many users will want to write their own programs where DrDAQ is just a part of the procedure. Using DrDAQ via a programming language is very straightforward as long as the language can make DLL calls. A functions library is supplied as Drdaq32.dll or Drdaq16.dll, depending on which version of Windows you are running. Unfortunately, there is no COM object or type library that can be used to control DrDAQ. A module file is provided for Visual Basic that defines all the DLL functions, and header and lib files are provided for C++. Examples and definition files for Delphi, Excel, LabView and HP-Vee are included. Essentially, any language that can call a DLL function can be used to program DrDAQ.

The only problem is that the documentation isn't extensive - you get an example to look at and then the rest is up to you to work out. To make it easier, let's look at how you would write a program in Visual Basic.
 

Basic training

Starting with a new .EXE project, load the module picodriverswin32drdaq32.bas. Use the command Project,Add Module. You also need to copy the DrDAQ32.dll to the WindowsSystem directory. Before you can use DrDAQ its driver has to be opened using drdaq_open_unit(port), which returns 1 if it was successful. When you have finished, the driver using a drdaq_close_unit(port) call. If DrDAQ is on LPT1 then the form load event can open it using something like:

Private Sub Form_Load()

Dim result As Integer
result = drdaq_open_unit(1)

If result <> 1 Then Stop

End Sub

The form's unload event handler can close it again using:

Private Sub Form_Unload(Cancel As Integer)

drdaq_close_unit (1)

End Sub

There is also a function: drdaq_get_unit_info(string,length,line,port) which returns information in the string concerning DrDAQ on the specified port. The string has to be a fixed length, and you have to specify its length in the call. You can add a button to the form and code its click event handler to get each line of information - DrDAQ has four. Print them in the debug area:

Private Sub Command1_Click()

Dim i As Integer

Dim s As String * 255

Dim ret As Integer

For i = 0 To 4

s = ''

ret = drdaq_get_unit_info(s, 255, i, 1)

Debug.Print s

Next i

End Sub

Now we come to the question of how to read the data from DrDAQ. The problem here is that the language in use might be slow compared to the sampling rate that DrDAQ can manage. As long as we only want to take readings at a rate within the scope of the language, things are simple. There is a drdaq_get_value(channel) command which returns the current reading of the selected channel as an integer. This integer has to be scaled, but that's all there is to it.

To try this out, add a button and the code:

Private Sub Command2_Click()

Dim value As Integer

value = drdaq_get_value(6)

Debug.Print value / 10

End Sub

The channel numbers correspond to the channels as listed in the PicoScope and PicoLogger. Thus, channel six is the internal temperature sensor. There are also function calls that return information about the sensor, such as maximum and minimum values and channel text. The drdaq_get_value_and_time function returns the precise time at which the value was obtained.

The problems start when you want to read data as fast as the input device can work. In this mode, you have to ask it to take a set of readings at a particular rate and then let it get on with it. When it is finished, you can ask for the data - as much or as little as you want to use. The first step is to specify the sampling rate using: drdaq_set_interval(time,samples,chanlist,no of chans)

Time (in microseconds) specifies how long the data should take to gather in total, and 'samples' specifies how many samples to take. Hence: drdaq_set_interval(10000,10... specifies 10ms and 10 samples, so we are requesting one sample every millisecond. The function returns the time taken to gather the samples. If you request a sampling rate that can't be achieved, the time taken will be longer than you specified. The next parameter is an array that lists the channels to be sampled, and the final parameter sets the size for the array. So to gather 10 samples every millisecond on channel one, you would use:

Dim ActualTime As Integer

Dim channels(1) As Integer channels(1) = 1

ActualTime = drdaq_set_interval(10000, 10, channels(1), 1)

Debug.Print ActualTime

Notice that the data is actually gathered by this call. To make the readings as specified by the set_interval function, you have to use the drdaq_get_times_and_values function. The first parameter is an integer array that will be used to store the times; the second is a long array that will be used to return the values; the third gives the size of the first two arrays. To get the times and values of the 10 readings specified by the previous set_interval, you would use:

Dim readings(10) As Integer

Dim Times(10) As Long

Dim ret As Integer ret = drdaq_get_times_and_values(Times(1), readings(1), 10)

For i = 1 To 10

Debug.Print Times(i), readings(i)

Next i

Every time you call get_times_and_values, a new set of measurements is made. If you specify multiple channels, the data that is returned is interleaved in the array. If you don't want the exact times at which the measurements were made, you can use the drdaq_get_values function. There is a drdaq_set_trigger function, which can be used to delay the data gathering until the input on the specified channel starts to change or reaches a threshold value.

The only additional commands you need to know are: drdaq_set_do(state) and: drdaq_set_led(state) which will set the digital output or the LED to the specified state; '0' is 'off' and '1' is 'on'.
 

Verdict

If you visit the Pico Web site, you will find details of science experiments that you can carry out using DrDAQ. If you already have one DrDAQ, you can win or earn another by writing up an original experiment for the Web site. You can also download demonstration versions of the software. Overall, DrDAQ is an excellent product. It is easy to use and makes it possible to use a PC in many interesting ways.

My only criticism is that the section in the helpfile that tells you how to make your own sensors is blank. You can make use of the raw voltage and resistance inputs to make your own sensors but, currently, the external sensor connectors are for Pico's own products. I hope that Pico sees the light and makes the information available very soon.

(Please note that since the DrDAQ review unit was supplied to the magazine, the help file has been updated to include the section on making your own sensors. If you have an old help file visit our download pages for a free upgrade

Reviewed UK Edition Computer Shopper Issue 151, Page 417