Buying an Oscilloscope

[theshame]

I've decided that I want an oscilloscope in order to further my understanding of electronics. Craigslist seems to be pretty awesome, people are selling them in working conditions for around $50-200. Most of them don't come with probes though.

Would it be wise to spend extra money for one that comes with probes? Do I need specific probes for a specific unit?

I've also never used a scope, so I plan on buying one that comes with a manual. But as an electronics novice (no formal education) is this something that takes a lot of knowledge? Or can I just probe around and see a waveform pretty easily?

[crochambeau]

Roll your own!

http://www.cromwell-intl.com/radio/probes.html

Here's another sort of a probe synopsis to give you an idea of what's going on in there:

http://scope-probe-schematic.blogspot.com/

I think the difference between companies are going to be in connector type, and possibly how the connector is wired. The input stages will probably reflect dissimilar qualities, so you may need to calibrate stuff differently from one to another.

I've been using my scope for ambiance and signal processing, not measurments, but I've been thinking about building some probes for it for a while now...  thanks for the reminder!

[crochambeau]

I've also never used a scope, so I plan on buying one that comes with a manual. But as an electronics novice (no formal education) is this something that takes a lot of knowledge? Or can I just probe around and see a waveform pretty easily?

Seeing a waveform is easy, accurate *measurements* of said waveform can entail a learning curve, and I understand it varies from scope to scope. I have old tube driven Tektronix scopes, the front panel controls are relatively easy to understand intuitively, but I've a hunch that calibration is orbiting a distant planet, so they are probably only good for comparative analysis as opposed to solid measurement.

A manual will be your friend, and a many are available online.

[crochambeau]

Update:

I had a go at rolling my own 10:1 ratio probe today following one of those linked sites, and it's less than spot on. The trace at top being what it does unless I physically ground myself to the scope or generator (even if I'm not touching the probe).



I've seen a bunch of 2 probe sets (a 10:1 and a 1:1) on the bay for less than $16 shipped. I just spent about an hour hollowing out an old pen, finding suitable resistors, engineering fits for stuff not made to go together, etc, etc, etc, so $16 is looking like a good deal to me. YMMV

[crochambeau]

Further update, I botched the first wiring of the resistive simple probe in the example above. I rectified that to follow, as I understand it, the schematic provided at the top of this page:

http://www.cromwell-intl.com/radio/probes.html

Now, I haven't gone so far as to ascertain that my existing BNC cable displays acceptable capacitance, nor to insure solid ground connection (now that I think about it) but this was what I achieved with it:



Upper trace being a solid feed, lower being the DIY probe with no additional electronics involved. Less than accurate I would say.

I'll report on the eBay probes in a day or two.

[sidandnancy]

When life deals you lemons...

Your probe is a lovely square to saw converter!

[crochambeau]

Indeed.

I see I forgot to update regarding my eBay purchase. Each auction was two identical probes that are switchable between 1:1 and 1:10, they work wonderfully.

I'll retain my home brew one for parlor tricks. 

[theshame]

Very interesting stuff here, thanks for documenting. I haven't purchased my scope yet, got really busy with work, and haven't had the time for much tinkering.