newb: oscilloscope vs data acquisition device
fess...@newsguy.com
I'm new to analog electronics though I'm formally educated in digital circuits.
I'm interested in a couple of projects like telephone coupling, amplifiers, and
elementary signal processing for 5.1/10.2 audio processing.
So I need some goodies! More than just the digital multimeter that cost me $20.
But I'm on a budget.
It seems like you can't go wrong with a tectronix 465 oscilloscope which can be
had on Ebay for $100 or so.
Then there are other options for scopes using my PC in Windows or Linux. I've
seen a lot on the bitscope, which can be bought or manufactured
(www.bitscope.com the sites down now you might try
http://www.google.com/search?q=related:www.bitscope.com/ for cached pages).
Slashdot has a great article on the subject at
http://slashdot.org/askslashdot/01/12/07/191220.shtml
So my question is, the next step up (much more $, worth it?) is a data
acquisition device like a National Instruments PCI-6025
http://sine.ni.com/apps/we/nioc.vp?cid=10971&lang=US
Or a similar card that you can program with MATLAB data acquisition toolkit
http://www.mathworks.com/products/daq/description1.jsp
I'm wondering two things:
* where should I start
* would a DAQ be practical for a newbie to use as a general-purpose scope?
I see that you really want to use a scope that operates well above 30mhz and if
it's digital should sample at 100mhz or more. The DAQs talk about 200 kS/s,
12-Bit sampling; how do these relate?
It also seems that a full-blown scope will take input of much higher voltages
than a flimsy PCI card. Trouble brewing for a newbie?
Opinions much appreciated.
Dave Thomas
Entrepreneur
the Wiz
attenuators to control the voltage levels that actually reach the internal
electronics.
Data acquisition devices collect (usually) known levels of (relatively) low
speed data in real time for display, storage, or response by another device.
Example: a temperature control unit in an industrial process or a very
sophisticated thermostat for your home heating/cooling system. You are required
to provide the input attenuation needed to bring the signals to be monitored
within the range of the data acquisition device.
If you want to see wide bandwidth or high frequency signals, a scope will be
your answer. If you want to record or generate responses to changes in signal
level, a data acquisition device is your answer.
For learning about data acquisition, www.dataq.com offers a 4 input,
serial-port-powered device for $25 (with software). They also have info on
programming in 32 bit Windows, using the provided control or a 3rd party control
(UltimaSerial).
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Bob Masta
DAQ cards typically need compatible software, which can
be expensive (or limiting, for cheap/free versions). As you
have correctly noted, they don't really replace a conventional
scope. So, for general-purpose work you probably ought to
go for a $100 Ebay scope.
But data acquisition systems can do a whole lot more than
a scope, if you can live with their speed limitations. For most
(human) audio work, a sound card is probably all you need.
(Note that sound cards don't have DC coupling, whereas
DAQ boards do.)
For example, my Daqarta shareware can give you real-time
display of waveform, spectrum, or color spectrogram.
More importantly, it can generate stimulus signals that stay
locked to the response. This allows it to do coherent or
synchronous signal averaging, where you present the
signal many times and combine the responses to reduce
noise... you can easily extract signals that are buried in
noise. (This is how biological "evoked potentials" are
recorded from the brain, for example.)
There are plenty of other features that are a result of
the readily-available processing power in a PC-based system.
If your particular application doesn't need wide bandwidth,
or DC response, this may be the way to go. (Actually,
Daqarta allows you to build a simple "board" from a resistor
ladder which *will* go down to DC, though it's only 8 bits.)
Personally, I have both on my bench. The PC system is
really handy for adjusting distortion, for example, by
looking at the spectrum display. And having a built-in
signal generator is really convenient, especially if you
want some special signal that a benchtop unit doesn't
provide. But I still wouldn't give up my "real" scope
when I need to look at high-speed stuff...
Bob Masta
tech(AT)daqarta(DOT)com
D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com