Electronics Forum / Basics / March 2008

On Mar 23, 1:47 am, garethrichardad...@hotmail.com wrote:

How much money do you have to spend?

Ideally you want two of them. A good traditional analog oscilloscope,
and a digital storage oscilloscope.
To analyse the output from IR remote controls requires you to capture
and display the signal, this requires a digital storage oscilloscope.
However the requirements of this are very simple and could be covered
with a cheap USB PC oscilloscope.

With both types you pay more for more *analog* bandwidth.
60-100MHz is a good starting point these days.
With digital oscilloscopes you pay more for *sample memory* and sample
rate. The more sample memory the better. Ensure that the sample rate
is at least 10 times the analog bandwidth. e.g. a 100MHz bandwidth
digital scope should have a 1GS/s sample rate. A good size sample
memory starts at say 8K and goes upwards.
You get much better value-for-money with a second hand oscilloscope
from Ebay or a surplus dealer, especially for analog types. e.g. you'd
be a bit foolish to buy a brand new 100MHz analog oscilloscope, they
are expensive.
But brand new 20MHz dual channel analog scopes are fairly cheap these
days, that is a decent starting point.
With eBay you take your chances somewhat, but buying from a reputable
dealer who has extensively tested (and possible calibrated) the unit
can be a good way to go.
Digital scopes are fairly expensive, and the second hand market is not
big, but if you have the money then get a good one over a USB based PC
oscilloscope. You need to buy a very expensive digital scope to get
good "analog like" performance, that's why I recommend getting a good
analog scopes too.

Dave.

A sound card based PC Scope would be ideal. The P/H to buy a even the
cheapest Hardware Scope would exceed the cost of the software for a PC scope

The IR remote runs around 15 KC so using a 100Mhz Scope would be like
using a 4 engined Water-Bomber to water the Lawn. Effective, just not
cost effective. Digital would be nice, but again it's like using a
Micrometer to measure cut firewood !

The 433Mhz PIC is just a Red Herring !
Yukio YANO

Get any decent secondhand Tektronix.

You can't go wrong with a Tek, much as the same way you can't go wrong
with a Fluke DMM.

Graham

You may want to consider having both a (used) hardware scope along
with a PC soundcard program.  (OK, I might be a tad biased since I am
the author of one such program!)   I have a 100 MHz "real" scope plus
a sound card system on my bench, and they both have their virtues.

The hardware scope is best for all general purpose work.  The sound
card system suffers from being AC coupled, and limited to audio-range
signals.  But if you are working in the audio range, there are some
powerful advantages:  It does spectrum analysis and color
spectrograms, as well as all sorts of tricks like histograms, and
synchronous waveform averaging to extract signals buried in noise.

If you are working on something where you need to monitor distortion,
a conventional scope's waveform display is *not* the way to go:
Depending on the type of distortion, you might miss several percent
distortion on a sine wave display, whereas on a spectrum display you
can easily see a tiny fraction of a percent.  Not only that, you can
see exactly which harmonics are causing the trouble (which can be
a clue to the source of the distortion).  

As an example, if you build a triangle-to-sine shaper using an
overdriven differential pair, there are a couple of interacting
adjustments that can be really confusing to adjust by just looking at
the waveform (or by ear).  But they are a snap if you can watch the
relative harmonics go up and down on a spectrum display.

And sound card systems can be dirt cheap, especially with the easy
availability of old computers these days.

And if that isn't enough to convince you, there's the fact that sound
cards can also *generate* sound... with lower distortion than
most benchtop audio generators, and *much* lower distortion than
function generators.  But they can provide much more control than any
function generator, not only in offering many types of waveforms,
including different kinds of noise, but also in types of modulation
like bursts, AM, FM, PWM or PM, or sweeps.  

(Product plug:  The Daqarta signal generator is FREE, even if you
never buy the system.  Oh, yeah:  Daqarta also includes a big-screen
DMM with true RMS, peak, and dB options, plus a frequency counter
that can resolve to milliHertz in a few cycles, even at low audio
frequencies.)

Best regards,

Bob Masta

             DAQARTA  v3.50
  Data AcQuisition And Real-Time Analysis
            www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
       Science with your sound card!

On 3月22日, 下午10时47分, garethrichardad...@hotmail.com wrote:

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You can get you a vellman PC500 scope for about 300 bucks wich is suppose to
be 50mhz(which is 50MSPS and I don't see how it sends all that through the
parallel port which runs at most a few mhz or so).

The only reason I recommend this scope now is because they finally
implemented a history function. When I first brought it I thought it would
have this feature but didn't. I complained on the msg board and was told
that it was impossible and I didn't understand how a DSO worked(by the
company). So I gave up and 2 years later I tried again and somehow got
through to the guy that maintained the software and he was able to implement
it. The software is definitely not the best though but works.

So the point is that with that scope you can use it both as a oscilloscope
and a logic analyzer(although a bit crude it does work).  This is really the
only benefit it has is that its cheap and can do the two most important
things needed for most apps.  It is definitely not the best though but you
get what you pay for. If you have more money then I'm sure there are other
products that would be better. (in fact you can get cheap dedicated logic
analyzers too now that use the pc)

I would have to say that the real issue with the scope is mainly the
software though.  But you can get used to it and maybe in the future they
will release the protocol used so people can write there own software. (they
do have something like it but not full featured)

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