I am a hobbyist and electrical engineering student that is looking
into purchasing a Velleman PCS500 oscilloscope that connects to the
computer. The specs can be found at
www.designnotes.com. This
company is having a sale and the price looks reasonable for what it
can do. The circuits that I am analyzing are not high speed and the
transient recorder included with this device looks attractive.
My question is this...Does anyone own or have any experience with the
PCS500?
I just hit the Velleman website to find info about this kit:
http://www.velleman-kit.com/common/product.Aspx?id=343036
Okay... Well, it looks good, and Velleman kits seem to be good
quality, but there are a few worries.
- You will want to keep this thing for a while. New versions of
Windows might not work with the software, and it's unknown how long
Velleman will support it. Communications to the computer use the
parallel port, and I'd bet that in about 5 years, it'll be tough to
find a computer with a parallel port - notice how most printers are
USB now? You might be stuck having to keep an old computer with an old
version of Windows in order to keep this thing useful.
- How fast is the communication with the parallel port? Not as fast
as an incoming waveform. How does it store the waveform it captures
before it transfers it to the parallel port? It appears that it can
sample only 4096 points per channel - presumably before it transfers
it to the computer. This could be limiting when it comes to dealing
with long period signals, or signals with a lot of detail. (I'm a
video guy, so I'm thinking of NTSC analog video here - would fill
quickly.)
- How good is the software? It's nice that it has all the features
described, but what if the software is flaky and GPFs or blue-screens
Windows constantly? Using your 'scope could then become an exercise in
frustration.
I'd recommend that you spend the $500 or whatever and pick up a
good used analog scope instead. Unless you're dealing in lots of
transients and one-shot events, a DSO isn't essential. The effectively
infinite resolution of an analog scope is also a lot nicer than the
pixellated waveform you'd see on a computer. Frequency response of
scopes is an issue, but in practice I find that 100MHz is the limit to
the usefulness of a scope - after that, the probe's capacitance loads
down the signal too much.
My main oscilloscope is actually a 35-year-old vacuum-tube based
Philips 20MHz dual-trace scope. I love the thing. It cost me nothing,
and after I replaced all the paper capacitors in it, it's rock-solid
and stable, and does everything that I need to do.
See if can find an analog 'scope with digital cursors - they make
life easier than trying to work off a graticule. My favorites are HP.
Tektronix are good too, but I keep on getting them with blown high
voltage power supplies and loads of difficult-to-replace proprietary
components - be careful. Avoid the Tektronics "chopper"-style analog
scopes which aren't really dual-trace - they have only one electron
gun and switch it back and forth between input amplifiers to emulate
dual-trace.
Happy hunting,
Lawrence
