SparkFun Forums

[brainwav]

Hi, I saw an add for a 10Mhz oscilloscope and was wondering if that is good for testing uC signals and basically debugging the circuitry? I mainly do little robots and use PICs or AVR's. Is 10Mhz too slow?

Brainwav

[leon_heller]

You really need at least 60 MHz bandwidth to see the sort of signals properly that you get when working with MCUs. A 10 MHz bandwidth scope will only let you see up to about a 3 MHz square wave properly.

I use a 100 MHz scope.

Leon

[Philba]

agreed.

also, you will definitely want a dual trace scope and an external trigger is really useful as well.

consider getting a used scope. tek or HP scopes last forever. ebay has a large assortment.

[zbalz]

Two questions on scopes:

For someone just starting to buy electronic supplies ...

1. Is EBay a decent place to buy scopes (any horror stories?)

2. Whats a general price range one should shoot for when hunting for an entry level scope? $100? $200? more?

[bigglez]

Greetings (No First Name Supplied),

Hi, I saw an add for a 10Mhz oscilloscope and was wondering if that is good for testing uC signals and basically debugging the circuitry? I mainly do little robots and use PICs or AVR's. Is 10Mhz too slow?

If you currently don't have a 'scope, then anything
would be better (assuming it works...)

A more important question is does it offer dual
channels (traces)? Most scope work is comparing two
signals in time, so to see both on the same screen is
necessary.

The bandwidth is less of a concern unless you are
attempting work where timing is critical. There are
easy work arounds to capture fast "glitches" if that
is thought to be the problem with your circuit, a
slow scope will slow everything down, and relative
timing of events will be faithfully maintained.

Second, make sure the scope has a trigger circuit,
without it the waveforms will be hard (or impossible)
to stabilize on the screen.

There are so many good scopes with 60MHz (or
more) that selling a ten meg scope seems silly.

Lastly, if you're interested in documenting the
scope's data consider a digital or PC based scope.
If you're more interested in investigating circuits
the budget will go further with a used analogue
scope from twenty years ago. Stay away from
tube scopes (they cost a lot to run, drift, and need
more frequent maintenance). Many analogue
scopes on the leading edge (during the Reagan
era) used exotic parts that are no longer
available. Scopes with dim CRTs may be useful
for hobby service, but will eventually go dark.

Comments Welcome!

[bigglez]

Greetings (No First Name Supplied),

Two questions on scopes:

For someone just starting to buy electronic supplies ...

1. Is EBay a decent place to buy scopes (any horror stories?)

2. Whats a general price range one should shoot for when hunting for an entry level scope? $100? $200? more?

eBay is only as good as it's sellers. Bad sellers are a
problem whether you're buying a five dollar or five
thousand dollar item.

You may find an estate sale where the one of a kind
scope was well cared for by a hobbyist. At the other
end of the spectrum you may find a good deal from
a broker that sells a ton of scopes on eBay, and is
there for the long haul. The one to avoid is the spot
seller that is after a quick buck and could care less if
the scope is 'good'. They may judge it by the simple
fact that a light comes on when plugged in, and have
no clue if the instrument is complete or functional.
In general if that same seller is also selling "used
tires" and "water skis", or any other oportunistic load
from the flea market for a quick eBay flip, they
probably should be avoided.

Pricing is tricky. The market for old electronics is
soft, so what cost "thousands when new" should not
cost more than a few hundred dollars now. One
hundred dollars can buy a very nice analogue scope
on eBay today.

Then again, you are competing with some commercial
buyers who cherish the old gear, or need spare parts,
and they will drive up the price.

A reconditioned scope (one that has been cleaned, checked
on the bench by a technician, and in calibration) will
always cost a few hundred dollars more.

Comments Welcome!

[winston]

If you're doing lots of digital stuff as well (with big fat buses, well, at least 8 and 16 bit buses) a logic analyzer's not a bad thing to have around. Last year I got a Thurlby LA4800 which has proved invaluable for 8 and 16 bit digital projects. I don't use it very often, but every time I've had occasion to use it, it's really proved its worth. The LA4800 is also pretty easy to use (with an on-screen manual), and quite commonly pops up on ebay.

I also bought a dual trace 20MHz Gould analog scope a couple of years ago (in very good condition) which I use quite frequently, since most of what I work on is 6 MHz and below it's been fine for my use. However, I am seriously considering an upgrade to a 100MHz instrument since I've been working on some higher frequency stuff recently.

[reklipz]

Are newer oscilloscopes like these, http://www.tek.com/products/oscilloscop ... 0_tds2000/, worth the money?

We've got a lab full of similar ones, in that they are using lcd screens instead of crts (the ones in the lab dont have pc connectivity, but allow saving a screen capture to a floppy disk).
I really like the ones we've got at my college, but if an old school tektronic oscope will perform just as well, I don't see any way to justify spending $1500+.

Is it worth it to invest in a new oscope?

[saipan59]

Go to your local HAM "swapfest".
I went to our local one last weekend. There were 3 or 4 "old and huge" scopes for really cheap.
One guy had two Tek scopes for sale. One was a Tek 475A (a very fine 250 Mhz dual trace scope, it's what I use at home), and he was asking $250 for it. He had them powered up and working.

If there isn't a local swapfest coming up soon, just make contact with the local HAMs in your area - I'm sure the old guys would love to have an excuse to get on the 2M repeater to see who has a scope to sell to a 'new guy'.

Pete

[awright]

All excellent comments above.

As one who grew up on tube 'scopes, I have a strong bias toward analog 'scopes for beginners. I agree that analog 'scopes from a decade or two ago, but not tube 'scopes, are the best value and performance for the money. I think it is too easy to confuse or fool yourself by misusing a PC-based 'scope and viewing aliases instead of the true signal.

I wouldn't pass up a 10 or 20 MHz analog unit to start with if the condition was very good and the price was right (say, well under $100). They are fine for audio and low radio frequency work and useful, but far from perfect, for some simple digital work. What you lose is the ability to see fast glitches, that are sometimes critical to detect, and the ability to faithfully reproduce fast digital signals. But you can still do lots of useful work with them. If possible, a faster 'scope is definitely better if you can afford it.

I concur that dual beams and triggered sweep are vital (but has anybody made a recurrent sweep 'scope in the last few decades, anyway?).

If at all possible, arrange to have a little bench time with a prospective purchase. Start out by looking under the hood to see if it is dirty or corroded. Smell it closely. If you smell the characteriestic burned insulation odor, pass it up. Look for signs of amateur repairs, burned circuit boards, overheated components.

Turn it on and run it through all the functions you can. Look for a clean, sharp, noisless beam, and clean, stable triggering from all type of signals.

In addition to the suggestions by others above regarding buying on ebay, I highly recommend only dealing with sellers who offer or will answer affirmatively to a query about accepting returns within a week or so of your receipt of the equipment, no questions asked. Guarantees that the equipment is "as described" but with minimal description except "lights up" are useless. Listings that are described as "as is - I'm too dumb to tell if it works," usually means that they tested it, found it to be trash, and want to dump it on some sucker. You will, of course, have to cover shipping both ways on a return, but that's better than being stuck with a non-functional instrument.

Never buy a 'scope with a burned out power transformer or CRT. It is never worth the cost of replacing them and you can not use general purpose replacement parts. Resistors, capacitors, and most discrete semiconductors are easy to replace or substitute for.

I've had pretty good luck buying used 'scopes over the decades. None of the dozens I have owned were new. A few were dogs, but most have been fine. Coincidentally, I just bought a 100 MHz Hitachi at auction that turns out to be dead, but the thrill of the gamble was worth the $27 price.

Have fun.

awright

[CommanderBob]

I have two scopes, both from E-bay. The first one I bought ($60) was a old (HUGE) 40Mhz Hitec scope. It worked great until one day I decide to tip it up a bit while it was on. Some lovely smoke and that familiar smell came from inside. Now it just buzzes when powered on.

The other scope I just got recently. It is the TDS 1012B 100Mhz scope from Tektronix. I think I got it for around $900 on e-bay. This thing is amazing. A digital scope is the way to go. This one lets you take screen shots and store them on a USB flash drive as .BMP images, very nice. It also can connect to your computer but I have not tried that yet.

Over all I would say buy the nicest scope you can afford, in reason of course .

Justin

[macegr]

I got a Tektronix 100MHz 465B for $100 on eBay, calibrated, good CRT, four probes, extra graticule, original manual, storage bag. It has served me well for the past five years. I also use a 100MHz 1Gsps Tektronix TDS2012 digital scope at work. I still end up using the 465B a lot, due to familiarity and the analog signal showing every little nuance of the input signal. A 100MHz scope is great for everyday use, unless you're dealing with high-speed electronics every day.