----- Original Message ----- From: "Lindy Mayfield" Subject: Re: [EE: ] what is a logic analyzer? > What would be the next logical piece of test equipment (after > a nice multi-meter) for a still-learning electronics hobbyist? > Would it be an oscilloscope? Depends a lot on what you do. For some folks, a counter is the next toy. With a PIC, it's pretty cheap and easy to make a reasonable counter. But an oscilliscope is tough to live without. > I've seen both scopes and logic analyzers that interface with > the PC -- they seem to be cheaper cause the PC does all the visual > -- and I wasn't sure the differences. A problem with PC scopes is usually the bandwidth. Unfortunately, this is also the problem with cheap scopes. The bandwidth of a scope tells you the maximum frequency for which it will faithfully reproduce a sine wave. However, you are rarely interestd in sine waves, unless you are mostly doing audio. Scopes fall off gradually above the spec frequency, so if you look at, say, a 50 MHz signal with a 20 MHz scope, you will see something. That something won't be the same shape and amplitude as the original, but it will be something. If you remember our old freind Fourier, you will recall that any periodic waveform can be looked at as the sum of a series of sine waves at integral multiples of the basic period. If you looked at a 20 MHz square wave with a scope that had a hard limit above 20 MHz, you would see a 20 MHz sine wave. Now real scopes don't have a brick wall, they fall off gradually, so you would see a square-ish sine wave on a 20 MHz scope. What this all means is that you would like a scope at least 3x the maximum frequency of interest. For most hobbyists, this means 100 MHz or so. If you can afford a large instrument, used 100-200 MHz scopes can be had fairly reasonably. Physically smaller scopes tend to cost a lot more. Tektronix scopes like the 465/475 are very popular for hobbyists on a budget. These are very nice, but they are quite large. One good way to get the lay of the land is to poke around on eBay. Look at the "completed auctions" to get an idea of what is available at what price. Typically, these things shoot up at the last minute, so auctions that haven't completed yet don't give you much of an idea. I'm always a little squeamish about buying stuff on eBay, although I have never had a bad experience. I've bought quite a few scope probes there, among other things. Another thing eBay is good for ... many of the scopes sold there are by dealers. You may find a dealer near you. 72/73 de WB8RCR http://www.qsl.net/wb8rcr didileydadidah QRP-L #1446 Code Warriors #35 -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.