Test equipment

A Logic Analyzer is really useful for certain tasks, but for my money, a basic o'scope is a required piece of equipment. My thoughts on order of electronic tool purchase based on how often I use them are:

A simple set of good quality hand tools

A good soldering iron

Good desoldering tools.

Digital Volt/Ohm meter

O'Scope

Logic Analyzer

I believe strongly in buying good tools and taking care of them. They will last a long time and not be a pain to use.

Soldering iron. Doesn't have to be an electonic temp controlled one, just not a $3.95 piece of crap that overheats and burns the tinning off the tip in minutes. Coated tips are a good sign. A decent iron in the

10-20 Watt range with a sponge to clean the tip on should be in the $20-$30US range.

Desoldering tools. Can be as simple as solder wick. The blue or maybe silver "Soldapullt" solder suckers are an excellent investment.

Digital Volt/Ohm meter. Personal preference goes a long way here, there are many decent meters on the market from about $30US up to several hundred dollars. Myself, I hate autoranging meters because I am always waiting for them to find the right range before they tell you what you wanted to know. Many people seem to like them.

O'scope. Analog scopes work well for most of what I want a scope for. Once in a while a digital scope would be nice - they show certain types of problems very well, but I still don't have one yet. Scopes are rated by their maximum frequency. Analog scopes will actually show higher frequencies than their rated top end but the amplitude accuracy suffers. If you are looking to see if a fast CPU bus bit is wiggling, an analog scope will show you. Digital scopes will lie to you if you exceed their sample frequency/2. They require some care in general use to be sure you really are seeing what is there. A new analog, 20MHz dual trace Asian scope can probably be had for about $400US. An old Tektronix 465 100Mhz dual trace analog scope can probably be had in the $150US range. The Tek

465 is a really fine scope within it's capabilities. The Tek 2465 scopes are really nice but as you say in the $500 - 800 range.

Logic analyzers. There are many choices depending on how fast, how deep and how many channels you want. Some problems require a logic analyzer, but not that many home type project ones do in my experience.

I am sure other people will add stuff I have forgotten or disagree with some comments. Some of the choices depend on exactly what you are doing at home.

Good Luck, Bob

Good reply....does anyone have suggests for a further suggestions?

One question I would have is what logic analyzers are available to amateur robotic builders from the used market?

TMT

Padu wrote: [snip]

Check EBay -- I got a used 100mhz tektronix for around $200 -- and that was a few years ago. A lot of scopes go up on eBay -- at $300 you should be able to get a pretty decent scope (which will end up being one of the most valuble instruments on your test bench).

Cheers -- tAfkaks

"MetalHead"

Thanks for the reply Bob.

My company has a few Tek 465B not being used right now because they are broken. They just sit there. I'm thinking if it would be cheaper for me to buy a 465 of EBay as tAfkaks suggested or to buy one of these broken 465B and send it to fix somewhere.

Also, I saw one goldstar for sale at Fry's for $365, I believe it is a 20MHz one. Would you still rather buy a used 100MHz tektronix?

Padu

9>

Personally, I'd go for the higher rate. Note that with a 20mhz scope, you won't be able to get much detail on a 20mhz signal.

Cant resist this one...

He actually wrote MHz, not mHz. To read anything off a 20mHz signal you would need a storage scope or a scope camera where you can keep the shutter open for a long time. ;-)

Actually, I didn't write mHz -- I wrote "mhz", an abbreviation generally accepted to mean "I'm too lazy to hit the shift key when posing to usenet unless absolutely necessary".

"The Artist Formerly Known as Kap'n Salty"

I believe he was refering to my post when I wrote MHz. Perhaps I'm unsure of exactly what 20MHz mean, but in my mind I was reading "20 mega Hertz". Is it wrong? What is 20mHz?

Actually, that's a good way to clarify something I didn't ask but I should know: 20MHz I suppose means 20000 cycles per second right? If yes then each cycle has 50ns duration. So a 20MHz oscope won't display signals that change faster than 50ns?

TIA

Padu

When speaking of oscilliscopes, the n MHz moniker specifies when the analog amplifier in the oscilliscope is only passing 50% of the signal through.

The typical analog amplifier for an oscilliscope looks roughly as follows:

Gain ^ | 1 +********************* | *** | ** | ** .5 | | * | | * | | * | | * | | * 0--------------------------+----+----> log(MHz) log scale X

For a 20 MHz scope, the point marked with an X above would be 20MHz.

What this means is that a 20MHz sine wave with a 1 volt peak to peak voltage will show up on the screen as .5 volts peak to peak.

A square wave consists of a Taylor series expansion of sines in multiples of the main frequency. When you run a 20MHz square wave into a 20MHz oscilliscope, it does not show up looking like a square wave, the edges are quite rounded with lots of "ringing" on the edges.

Given that many microcontrollers are runing in the 10-50MHz range, and that it is farily easy for these microcontrollers to spit out signals in 10-25MHz range, a 20MHz oscilliscope can give a very distorted view of what is going on.

I recommend a 60MHz or 100MHz oscilliscope or better. If you have to choose between a used 100MHz vs. a new 20MHz., you might be better off with the used 100MHz. There is a very active market for used Tektronix 465's. If you live in a metropolitan area, there is usually an outfit that can fix up an out of tune Tek 465 for a reasonable sum of money. Shop around for the oscilliscope repair service *before* purchasing a used scope. Indeed, the repair service might have a good deal for you.

For the record, I purchased a 100MHz B&K scope 25 years ago and it is on its last legs. I will either have mine repaired, or purchase a used 465 and have it tuned up. I keep looking at the BitScope product line:

for a digital oscilliscope, but I think I want more bandwidth before making such a purchase.

I hope the information above is usefule to you,

-Wayne

Seems like I just bought one of these little guys:

One thing that was common to all oscopes for sale on ebay: nobody know how to test it (oh sure). I don't know what kind of junk I bought, but for $75 it is worthy the risk I guess. Even if I have to spend one or two hundreads for fixing it I believe it is still worthy, don't you?

Padu

A used Tek 465 is a good risk. To test, I recommend purchasing a

20MHz crystal oscillator module from Digikey or Jameco. These come in metal cans with 4 pins (Ground, +5V, signal) and fit easily into a 14-pin DIP socket or a breadboard. Apply 5 volts and look at the signal on your scope. If it shows up as a crisp square wave form with just a little ringing, you got yourself a winner. If not, it may be time to find your local oscilliscope repair/tune up shop and ask for a quote.

Later,

-Wayne

"Wayne C. Gramlich"

Thanks for the hint. I have a few xtals at home that I'll use to test it as soon as I receive it.

Make sure you get a 465B, not a 465, and that the seller has 99%+ positive feedback.

In a heartbeat.

you can buy a bitscope for a similar price, which uses a computer as the storage and analysis part of the dso/logic analyser.

20 milli Hertz (written "20mHz") is one cycle every fifty seconds. 1 milli Hertz (written "1mHz") is one cycle every one thousand seconds (nearly seventeen minutes) 20000000 cycles per second (twenty million, not twenty thousand as you have written)

That bit is correct.

HTH Deep.

And now you're going to be spending another $50 or $75 for the probes and manual that aren't included. ;-)

- Rich

If the scope works, he won't need the manuals -- he ought to be able to figure out an analog scope without them. Probes aren't very expensive these days.

Someone who has never used a scope before is going to need a manual, without question, if he's planning on doing anything more than measuring voltage, I expect.

And yes, probes are cheap, but you generally get what you pay for. A decent probe set rated to 100Mhz is going to cost about what he paid for the scope in the first place.

Which isn't to say that he didn't get a good deal - personally, I still use my 465. But I hope he's not just planning on sticking some wire into the probe sockets and expecting it to work. ;-)

- Rich

Christ!

You're too lazy to type MHz instead of mhz, but you spell eBay as EBay?

Get a life.

Tom, (not tom)