Tektronix 2215a For Analog Portion of Learning the AoE - Page 1
Forum section: electronics / beginners

author: baeckel
author_rank: Newbie
timestamp: July 13, 2017, 07:39:16 pm
content: Hey all,I'm trying to put together my lab based on what I'll need to work through the "Learning the Art of Electronics book". I have a Tektronix 2215a in my basement and here is what I know about it:It is a 60MHz scopeIt has 2 channelsIt will cost me $0 to useWill that be enough to get me through the analog portion of the LtAoE book?I'm assuming I'll need to upgrade to something like the Rigol DS1054z for the Digital section.Is that assumption correct?Thanks!--Jonathan

author: tggzzz
author_rank: Super Contributor
timestamp: July 13, 2017, 09:10:40 pm
content: Quote from: baeckel on July 13, 2017, 07:39:16 pmWithout having read LtAoE, a working Tek 2215a will be very useful.Ifit isn't sufficient for everything, then (a) you will know exactly what youneed, and (b) you might be able to find a way of working around the problem.QuoteMaybe, maybe not.You need a fast scope to assure digital signal integrity. That rigol would be no better than the Tek.You need a storage scopeora way of making the signal repetitive,orto work in the digital domain, not the analogue domain. Frequently it is possible to find a way to make the signal repetitive. Often it is best to debug in the digital domain using a logic analyser or printf statements.You will probably need some form of function generator. If you can get the educational discount, the Digilent Analog Discovery has many virtues. It has two AWGs, 100MS/s digital pattern generator and logic analyser, plus a 10MHz 14-bit dual channel digitising scope and associated post-processing software.My preference, which others will dispute, is a medium speed analogue scope (BW >250MHz), plus an Analog Discovery for single shot capture etc.Don't forget the cost of the probes.

author: alm
author_rank: Super Contributor
timestamp: July 13, 2017, 10:26:50 pm
content: I am pretty sure you can do at least 95% of the analog labs with an analog scope. Many will involve feeding the circuit a signal from a function generator and observing the result on a scope, which works just as well with an analog scope. In the equipment chapter at the end they specifically mention analog scopes.For digital labs you might well get by with an analog scope + cheap logic analyzer (e.g. one of the < $10 eBay ones with Pulseview software).

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 13, 2017, 11:04:45 pm
content: I don't understand the obsession with scopes for digital stuff. Get a logic analyzer. Simple, smaller, cheaper, more channels, it's the right tool, done.

author: baeckel
author_rank: Newbie
timestamp: July 13, 2017, 11:18:33 pm
content: Thanks Tggzzz & alm, that was helpful.Alex, it's not so much of an "obsession". I have one in my basement and I want to know whether or not it will work for the labs in the book. IMHO one doesn't really know what the right tool is unless they know exactly what the job is.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 14, 2017, 12:08:25 am
content: Quote from: baeckel on July 13, 2017, 11:18:33 pmSorry, didn't mean specifically you. It's just that I see people using scopes for digital stuff all the time and it's quite puzzling. It's a big object, with millions of functions and buttons, yet mostly only has 2 or 4 channels in most cases.I mean thishttp://www.ebay.ca/itm/24MHz-8CH-USB-Logic-Analyzer-24MHz-8-Channel-Compatible-to-Saleae-ARM-FPGA-M100/272337085235?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649already has twice the inputs of a DS1054Z.... for 6$. Even if it's crap, it's crap that'll let you see simple serial ports, I2C and SPI, right on your PC.Of course, if you design something that's using strange voltage levels, or may have signal integrity issues, then the logic analyzer is the wrong tool; but it's trivially easy to stick to well-established standards and layout/decoupling/routing rules-of-thumb.Plus the leads for the logic analyzer are so much smaller and lighter, they stay in place.I paid a lot more for a 34 channel analyzer with nice grabber leads. The other week I used it to check the outputs from a radio I was using for a quadcopter. It's great. So much faster and smaller.Scopes, or more specifically communications analyzers, or BERTs, etc, become useful for digital stuff when you get into Gbps rates, since here analog effects dominate again.But for the run of the mill Arduino, vintage 8 bit hacking, serial ports, I2C, SPI, glue logic, for me, a logic analyzer beats a scope.May the artillery point at me and commence firing!

author: baeckel
author_rank: Newbie
timestamp: July 14, 2017, 12:36:26 am
content: Right on Alex, I'm all with you for not buying things you don't need! I'm just trying to figure out what I do/don't need to get through this book. I'll look into supplementing my old scope w/ a cheap logic analyzer. What analyzer did you end up using on the quadcopter radio? I'd gladly trade some money for some quality.

author: tggzzz
author_rank: Super Contributor
timestamp: July 14, 2017, 08:52:18 am
content: Quote from: baeckel on July 13, 2017, 11:18:33 pmI expect you already have the very powerful attitude of "I need to do X, and have Y; so how can I use Y to do X even though Y isn't perfect for the job". Doing more with less is intellectually stimulating and satisfying.Regarding Rigols for protocol decodes, be aware of the second to last paragraph inhttps://www.eevblog.com/forum/testgear/a-possibly-dumb-q-on-digital-oscilloscopes/msg1255927/#msg1255927I fully expect the only-decode-the-screen is true, and for me it makes the device little more than a toy in that application.

author: rstofer
author_rank: Super Contributor
timestamp: July 14, 2017, 08:21:24 pm
content: I would just use the scope until it won't get the desired results. Then you know what the desired results should be.I don't agree with the comment above that the Rigol won't be superior to the 2215, it will. In a couple of ways:1) Digital scopes can take a one shot capture. This is extremely important. Particularly when triggering on glitches.2) While logic analyzers are nice, so is the ability to decode SPI or I2C without having to drag out the analyzer3) The 1054Z, when unlocked, is a 100 MHz scope. 100 > 60, simple as that! This whole bandwidth thing becomes very important with digital signals because it takes a ton of bandwidth to display even a 20 MHz square wave. The 100 MHz Rigol really isn't enough since it will only display the 5th harmonic. The display gets to looking rounded off. That new Siglent SDS1202E-X (if I got that right) at 200 MHz (2 channels) is looking pretty good. 200 > 100...I got along with a 10 MHz scope for a long time before I bought my used Tek 485 (300 MHz). I used that for about 10 years until I bought the 1054Z. But I didn't get rid of it! 300 > 100I would expect most analog work to be done at well under 60 MHz (like, maybe 1 MHz) and since it will often be sine waves, harmonics may not be an issue. Even if the signal is modulating a carrier, you don't always have to see individual cycles of the carrier to know that it is there. Still, a 60 MHz carrier is a long way up in the frequency spectrum. Not GHz, of course, but still pretty high for a lab class.I think you will be fine for a very long time.

author: tggzzz
author_rank: Super Contributor
timestamp: July 14, 2017, 08:49:14 pm
content: Quote from: rstofer on July 14, 2017, 08:21:24 pmMy comment about the Rigol being no better than the Tek was in the context of assuring signal integrity. The next paragraph stated a need for a storage capability.As far as signal integrity of modern jellybean logic is concerned, 100MHz is only a little better than 60MHz. With sub-nanosecond risetimes, even 350MHz is barely adequateAnd who cares about the frequency of a square wave -all that matters is the transition time. Poor signal integrity on a 1Hz signal can screw you just as effectively as poor signal integrity on a 100MHz signal.

author: xani
author_rank: Frequent Contributor
timestamp: July 14, 2017, 11:14:50 pm
content: Quote from: Alex Eisenhut on July 13, 2017, 11:04:45 pmIt is right tool, but it is nice to have oscilloscope even just to verify signal integrity. Of course, all depends, if you run 100kHz serial bus over 5cm on PCB it will probably just gather dust

author: tggzzz
author_rank: Super Contributor
timestamp: July 15, 2017, 12:24:10 am
content: Quote from: xani on July 14, 2017, 11:14:50 pm5cm is sufficient to have signal integrity problems with some jellybean logic, e.g. the 74lvc1g family. In pessimal cases, I've seen 7V from a gate with a 5V supply over a shorter distance than that!The 100kHz is irrelevant; all that matters is the <1ns rise/fall times.

author: JPortici
author_rank: Super Contributor
timestamp: July 15, 2017, 05:38:57 pm
content: Quote from: Alex Eisenhut on July 13, 2017, 11:04:45 pmwhat if i want to see the correlation between the digital bus and other analog waveforms? easier to do with a single instrument. a lot harder to do if you don't have options to trigger scope and LA at the same timealso, every time i have problems i hook up the scope and look at the actual waveform. is it a signal integrity problem? is it a software problem, so let's say my I2C state machine has a bug and both peripherals and mcu prin drivers are pulling down so i see a stronger "zero" appearing instead of just a logic zero?in these cases being able to trigger on events instead of simple triggers helps you a lot

author: tggzzz
author_rank: Super Contributor
timestamp: July 15, 2017, 06:37:58 pm
content: Quote from: JPortici on July 15, 2017, 05:38:57 pmIt is always easy to dream up use cases where having a piece of equipment isnice. What is more interesting is whether a piece of equipment isnecessary. People often don't distinguish between "nice" and "necessary", not only when thinking what they (might) need but also when explaining their thoughts to other people.All equipment has its disadvantages, some technical, some learning curves, some financial - especially for amateurs where they have to strongly prioritise what they can afford.

author: rstofer
author_rank: Super Contributor
timestamp: July 15, 2017, 07:16:47 pm
content: Quote from: xani on July 14, 2017, 11:14:50 pmA logic analyzer isn't always a good answer. Assume it is using an internal clock, as most cheaper LAs do, then perhaps it samples at say 100 Mhz. So clock signals are 10 nS apart. There is also setup time to consider, it is not zero, even on a LA. So, when you see rising and falling edges, you can't really be certain where the real edge in relation to the clock. This matters when you want to see setup time. Maybe the signal JUST missed the last clock so that it is now displayed 10 nS later. Or, maybe the clock signal missed the sample clock and shows up 10 nS later. Does that matter? Sometimes...Does the analyzer accept an external clock? If not, it is nearly useless for analyzing state machines. In this analysis, the only thing that matters is where the inputs are (state and outside inputs) when the state machine clock goes high. Again, sampling the state machine clock and trying to align edges is fraught with error.Sometimes a scope is just a better way to prove setup time. The problem comes about when the signals start to get rounded off due to bandwidth restrictions. It is entirely possible that a data signal has much lower frequency content than the clock which might mean the the data signal looks like a square wave and the clock looks like a sine wave.