Everything in life is not
digital. These days it’s too easy to expect the world of electronics and
computing to use digital signals exclusively. Digital signals are easy in
the sense that they only have two distinct voltage levels. For example TTL
logic has +5 volts to represent logic ‘1’ and zero volts to represent
logic ‘0’. However, there are times when an analogue signal is inescapable
and needs to be measured. For example a temperature sensor typically
provides a continuously varying voltage proportional to the measured
temperature. If a control system must respond to these changes then
fundamentally it needs to be able to quantify this voltage. For our
example we will show how a PC can be used with a
W.A.S.P. USB adaptor
board to measure an analogue voltage varying between 0 and 5v and obtain a
numerical measurement for this in the corresponding range of 0 – 255.
WASP is an acronym for Windows Analogue Signal Processor and the adaptor
board can measure 4 independent analogue voltage inputs. (The board also
has other facilities, which we will leave to other discussions).
Connecting Analogue signals to WASP
The WASP has four analogue inputs which are connected via the screw
terminals TL1. For our purposes we will use analogue input 1. This is
connected to TL1 Terminal 7. Since every analogue signal must have a
ground reference this will be TL1 terminal 9. To allow us to generate a
variable DC voltage to be measured, we will use a simple potentiometer
supplied from a 5v source. This circuit is shown below.
By turning the potentiometer the voltage on terminal 7 will vary between 0
and 5v. This is what we will be measuring.
Connecting the WASP to the PC
The WASP is a standard USB device and will automatically configure itself
for Windows operation as soon as it is connected to a free USB port on the
PC. There are no additional drivers to install for the WASP as these are
already part of the Windows operating system (WinXP or later).
Running WaspWare Software.
Supplied with the WASP is WaspWare software. Installing this from the
installation disk simply consists of clicking on the “Next” button for a
few screen prompts for the default installation.
When you run the WaspWare software you will be presented with a screen
showing (amongst other things) four vertical sliders.
click on image for higher resolution version in new window
The four vertical sliders correspond to the four analogue inputs to the
WASP. Since we are using input one we will be using the first slider on
the left. When running the height of the slider is directly proportional
to the amplitude of the voltage input. The numerical value of this input
is also shown directly beneath the slider . This number is in the range
All that is required now is to click on the “Run” button on the bottom
left of the screen to start measuring the analogue voltage. When you click
on “Run” the message window adjacent will show “Running”. Now you can vary
the voltage at the input by turning the external potentiometer. As you
turn the potentiometer the vertical slider will move up and down
corresponding to your changes and the numerical readout below will show
the actual value of this voltage (in range 1-255).