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RogerN wrote:
> "Rich Webb" <(E-Mail Removed)> wrote in message > news  (E-Mail Removed)...>> On Sun, 7 Feb 2010 15:31:46 -0600, "RogerN" <(E-Mail Removed)> wrote: >> >>> What's the best scope to get for the money for mostly digital circuits? >>> I'll have some analog but nothing real high frequency, like analog >>> connections to the microcontroller, maybe some SMPS circuits. I was >>> looking >>> at some microcontroller and fpga designs that you can get kits starting at >>> less than $100 and going up with more speed and features. Also, I see on >>> eBay you can get some nice looking Techtronics scopes for $350 or so, 4 >>> channel digital, etc. Just wondering if something like the AVR scope >>> would >>> be a useful tool or if I would be wishing I went ahead and bought a nice >>> used scope on eBay. >> "The" AVR scope? Hard to comment on it, knowing only that... >> >> In general, though, USB-based scopes typically don't have particularly >> high sample rates. I'd suggest looking into one of the smaller "real" >> digital 'scopes, such as Instek or Rigol. There was a loooong discussion >> on this back in December in this group with the subject "A good digital >> oscilloscope?" (As you may imagine, this comes up fairly often here.) >> >> A USB logic analyzer, on the other hand, is a useful gadget. I've been >> using an Intronix for years and wouldn't go anywhere without it. Overdue >> for a new model, though. http://www.pctestinstruments.com/ >> >> -- >> Rich Webb Norfolk, VA > > Here's some of the stuff I was looking at, some stand alone, some use PC: > > http://www.youtube.com/watch?v=fxViYQ5WWOE That looks closest to a whole oscilloscope. > > http://www.fpga4fun.com/digitalscope.html Looks like an interesting toy for dedicated use. You'll be disappointed with all the hassle of trying to use it as a general purpose scope. > http://cgi.ebay.com/Pocket-Oscillosc...item25589f14ff > This is a TOY. 1MHZ sample rate...useless... > But I thought this looked pretty nice: > http://cgi.ebay.com/Tektronix-2465-F...item20af54a6f4 > 2465 is a VERY nice scope. Beware that they have a part that goes bad and it's made of unobtanium. Only way to get the chip is to buy another scope with a chip that hasn't failed YET. I sold mine while it was still working. > RogerN > > Buy one of the toy scopes above if ANY of the following are true. 1 You are an experienced measurement tech and you know every measurement you'll ever want to make and can verify that the unit can measure it. 2 You have too much free time on your hands, are tired of playing solitaire and need a better time waster. 3 You want hands-on experience with the easy part of crappy digital oscilloscope designs. 4 You want to spend more time futzing with the scope than working on the project. Never make your first scope a KIT unless #1 applies. Never make your first scope a computer accessory unless #1 applies. Never buy a digital (or analog) scope that doesn't let you view what happens before the trigger event. There may be exceptions, but a scope that doesn't have an input attenuator and specified input capacitance is a poor choice. Getting the signal into the acquisition unit and scaled appropriately is HARD for the novice. Last thing you need is a scope that smokes every time you touch the 12V power supply. Don't buy a cheap scope on EBAY. Freight costs more than the scope is work, even if you do get lucky and it works. A scope that's guaranteed to work ain't gonna be cheap. Be especially wary of "can't test it, don't have time to test it, don't have equipment to test it". That's code for "broken". I once asked about a "can't test it" scope on ebay. He accidentally replied from an email account at the world's largest used test equipment dealer. Seems that they sell the bad stuff out the back door on ebay. If you want to make oscilloscope measurements, buy a real commercial scope. I prefer analog for a first scope. Find a local ham and put out the word you want a scope. Most of us have more scopes than we can ever use. Maybe you can borrow one 'till you figger out what you need. Geography matters, but put a request for a scope on Craigslist or equivalent. You have a LOT more options if you are experienced, already have a scope you can use to fix a busted new scope etc. If you're a novice, go get a 30-40 year old analog scope CHEAP. |
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RogerN wrote:
> "mike" <(E-Mail Removed)> wrote in message > news:hkooth$5qh$(E-Mail Removed)... >> RogerN wrote: >>> "Rich Webb" <(E-Mail Removed)> wrote in message >>> news (E-Mail Removed)...>>>> On Sun, 7 Feb 2010 15:31:46 -0600, "RogerN" <(E-Mail Removed)> wrote: >>>> >>>>> What's the best scope to get for the money for mostly digital circuits? >>>>> I'll have some analog but nothing real high frequency, like analog >>>>> connections to the microcontroller, maybe some SMPS circuits. I was >>>>> looking >>>>> at some microcontroller and fpga designs that you can get kits starting >>>>> at >>>>> less than $100 and going up with more speed and features. Also, I see >>>>> on >>>>> eBay you can get some nice looking Techtronics scopes for $350 or so, 4 >>>>> channel digital, etc. Just wondering if something like the AVR scope >>>>> would >>>>> be a useful tool or if I would be wishing I went ahead and bought a >>>>> nice >>>>> used scope on eBay. >>>> "The" AVR scope? Hard to comment on it, knowing only that... >>>> >>>> In general, though, USB-based scopes typically don't have particularly >>>> high sample rates. I'd suggest looking into one of the smaller "real" >>>> digital 'scopes, such as Instek or Rigol. There was a loooong discussion >>>> on this back in December in this group with the subject "A good digital >>>> oscilloscope?" (As you may imagine, this comes up fairly often here.) >>>> >>>> A USB logic analyzer, on the other hand, is a useful gadget. I've been >>>> using an Intronix for years and wouldn't go anywhere without it. Overdue >>>> for a new model, though. http://www.pctestinstruments.com/ >>>> >>>> -- >>>> Rich Webb Norfolk, VA >>> Here's some of the stuff I was looking at, some stand alone, some use PC: >>> >>> http://www.youtube.com/watch?v=fxViYQ5WWOE >> That looks closest to a whole oscilloscope. >>> http://www.fpga4fun.com/digitalscope.html >> Looks like an interesting toy for dedicated use. You'll be disappointed >> with all the hassle of trying to use it as a general purpose scope. >> >> >>> http://cgi.ebay.com/Pocket-Oscillosc...item25589f14ff >>> >> This is a TOY. 1MHZ sample rate...useless... >> >>> But I thought this looked pretty nice: >>> http://cgi.ebay.com/Tektronix-2465-F...item20af54a6f4 >>> >> 2465 is a VERY nice scope. Beware that they have a part that goes bad >> and it's made of unobtanium. Only way to get the chip is to buy another >> scope with a chip that hasn't failed YET. I sold mine while it was still >> working. >>> RogerN >>> >>> >> Buy one of the toy scopes above if ANY of the following are true. >> >> 1 You are an experienced measurement tech and you know every measurement >> you'll ever want to make and can verify that the unit can measure it. >> >> 2 You have too much free time on your hands, are tired of playing >> solitaire and need a better time waster. >> >> 3 You want hands-on experience with the easy part of crappy digital >> oscilloscope designs. >> >> 4 You want to spend more time futzing with the scope than working >> on the project. >> >> Never make your first scope a KIT unless #1 applies. >> Never make your first scope a computer accessory unless #1 applies. >> Never buy a digital (or analog) scope that doesn't let you view >> what happens before the trigger event. >> >> There may be exceptions, but a scope that doesn't have an input >> attenuator and specified input capacitance is a poor choice. >> Getting the signal into the acquisition unit and scaled appropriately >> is HARD for the novice. Last thing you need is a scope that >> smokes every time you touch the 12V power supply. >> >> Don't buy a cheap scope on EBAY. Freight costs more than the scope >> is work, even if you do get lucky and it works. A scope that's >> guaranteed to work ain't gonna be cheap. Be especially wary of >> "can't test it, don't have time to test it, don't have equipment >> to test it". That's code for "broken". >> >> I once asked about a "can't test it" scope on ebay. He accidentally >> replied from an email account at the world's largest used test equipment >> dealer. Seems that they sell the bad stuff out the back door on ebay. >> >> If you want to make oscilloscope measurements, buy a real commercial >> scope. I prefer analog for a first scope. >> >> Find a local ham and put out the word you want a scope. >> Most of us have more scopes than we can ever use. >> Maybe you can borrow one 'till you figger out what you need. >> >> Geography matters, but put a request for a scope on Craigslist or >> equivalent. >> >> You have a LOT more options if you are experienced, already have >> a scope you can use to fix a busted new scope etc. >> If you're a novice, go get a 30-40 year old analog scope CHEAP. >> > > Lot of good info there, thanks. I have a 10mhz leader single trace scope > that worked fine last time I tried it. Drag it out and use it. You'll quickly learn what features you need. Do you have any recommendations on a > used repairable scope? Already done that TEK 465, 7704 and relatives. The 7704 is handy 'cause you can get plugins for logic analysis, spectrum analysis, TDR, curve tracer etc. I've seen some recommend the Techtronics 465, since > a lot of what I plan to use it on is digital signals/communication, I > thought storage would almost be necessary. You need to say a LOT more about what you mean by digital signals/communication. RS-232 is communication and well within the capability of your leader. Demodulating Cellphone signals is quite another matter. An oscilloscope is a poor substitute for good design judgment. It's a time domain instrument that is very good at looking at individual transients. You want to know the risetime, amplitude and "cleanliness" of signals. An oscilloscope with a delay line will let you do that, as long as it has sufficient bandwidth for the risetimes you're observing. Two channels will let you see relationships between two signals. As long as you stay away from the maximum speed stuff will run, you'll have few problems that need high resolution timing. Once you get beyond that, it becomes complicated real fast. Just probing the system is a nightmare. Your problem is triggering on the desired event. You quickly get into logic analyzer types of triggering and display. A two-channel scope is better than one. 4 is better, but still not too helpful if you need to trigger on 8 or 64. I once got so frustrated that I built a fixture with a PAL on it. Reprogrammed the PAL for each complex trigger and used that as one channel into a logic analyzer. Digital storage has some benefits. Lets you see what happened to signals WAY before the trigger event. But you still have to come up with some way to trigger on the symptom. Lets you see signals WAY to slow to be visible on an analog scope. I futzed around with a battery tab spot welder for years. About 10 minutes after I got my first digital storage scope, it was working a LOT better. I could see what was happening. Post processing can come in handy. It's kinda nice to set a square wave to exactly 50% by punching the FFT button and nulling odd harmonics. But digital storage has lots of issues with aliased displays, triggering, single shot sampling rate, display update rate...the list is endless. If you know what to expect, you can deal with it. But I still get confused sometimes. What you need depends on whether you're debugging your own design. I use PIC processors for most of my hobby stuff. I don't run them faster than they're designed to go. I fix problems by inspecting the code and using "print statements". If needed, I can use a pin to generate a scope trigger exactly where I want to look. I rarely use more than two scope channels. If you're reverse-engineering or repairing someone else's stuff, you may need a LOT more capability. For most of my stuff, I use a TEK 308 logic analyzer. It decodes RS-232 and GPIB. It generates word triggers into a TEK TDS540 digital scope. It's OVERKILL for most things. You can do a lot of stuff with a cheap analog scope. Complex stuff needs $60K equipment. There ain't much in between. Might as well go cheap and suffer the consequences of not being able to do some stuff. Patience pays off when you're looking for equipment. My TDS540 was free...the 308 was $5...plus about $10 in parts and a week to get it all working...but that's not the norm. Fixing undocumented stuff is not for the faint of heart. > > RogerN > > |
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