Hi people,
Sorry for my silly question ... I thaught if i say too much it would
make it even more obvious how little i actually know about this stuff
But here goes, i'll try and explain the kind of thing i want todo ..
What i want to do is see a reading of signals from things like optical
sensors and digital outputs from various things ..
I could do this with a multimeter if the signal was there for any
decent amount of time ..
But as i *think*, an oscilloscope can help me here to 'slow down' time
and see what is going on ?
Or, rather, think of an o'scope as a really fast voltmeter.
So im interested in getting a little graphical graph displaying
voltage over time, for use in low current digital circuits. 0v-12v
max.
For example;
An optical sensor mounted on something and a wheel with a hole in it,
spinning infront in such a way that on only ONE part of the wheel
where the hole is the optical sensor would be triggered (or
untriggered, whichever) .. how can i SEE that the sensor did infact
work ...
While I *know* that others will disagree, I'd recommend that you bite
the bullet and get a decent digital scope rather than spend $19.95 on a
third-hand, 30-year old analog scope with dodgy electronics.
Recommendation: a Tek TDS1002 or TDS1012.
It uses "real time" digital sampling. That allows you to trigger on and
capture a single event rather than relying on the repaint from a
continuous series of waveforms. Very handy when working with digital
electronics to be able to capture one particular wavetrain, e.g., one
character on a serial data line or one transition on your optical
sensor. It's nice to "know" that an event happened but it may also be
useful to know exactly how wide that one pulse was and what the rising
and falling edges look like.
I am looking at getting a "Velleman HPS10"
(
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2557720053&category=4677),
this has a 10mhz processor built in, does this mean i can read samples
upto 10 mhz ? so this would suite my needs of operating with PIC chips
at 4-8 mhz ?
You need to look at two numbers; the sample rate is one but the analog
bandwidth is equally important. That defines the characteristics of the
front-end electronics. At 2 MHz, this is at the limit of an 8 MHz PIC
(four clocks per instruction cycle, so an output port can't be toggled
faster than 2 MHz, IIRC).
A rule of thumb is that you'll want a bandwidth that's at least 5X the
target signal frequency, so at least a 10 MHz bandwidth would be
preferred. That is *not* the same as the 10 MHz sample rate (which is
how fast the internal electronics sample the incoming signal).
See also: Nyquist.
The Vellman is only a single channel. Sometimes that's OK but often
you'll want to see what's happening HERE when something changes THERE
and how long after THIS that THAT happened.
For this kind of usage, are the clamps useless ?
No, but clamps measure current whereas standard probes measure voltage.
Each has uses, but a current probe won't tell you the state of a logic
port as well as a the boring old standard probes will. Ignore the
perceived coolness factor of clamps; virtually every o'scope is supplied
with probes and not clamps because most of the time, probes are the
appropriate sensor.
