Oscilloscope recommendations
doggiedoc
Posts: 2,241
I think I would like to have a decent scope to help me understand (and learn) what is happening while I learn more about smart pins and the P2.
I saw @rogloh posted what looks like screen shots from a scope in another thread.
@rogloh said:
This looks like something I could benefit from. Any recommendations on what to buy?
Paul
Comments
I believe that capture is from a logic analyzer -- perhaps Saleae.
-- https://www.amazon.com/Saleae-Logic-8/dp/B0749G85W2
I bought one of these for work. It's a bit pricey, but a nice piece of kit. When I go to cons, I carry this $13 LA with me:
-- https://www.amazon.com/gp/product/B077LSG5P2
I don't worry much about losing it given it's cheap to replace. And it does work well enough for experimenting. I went out-of-state to see friends for Thanksgiving a couple years ago and had this with me. Someone in the forums (Bob?) needed assistance with a set of smart LEDs that were not well known, but he had a link to a reverse-engineered protocol document. With that document and the $13 LA to examine the output, I was able to write a driver that worked. That was kind of neat.
I use a piece of freeware called Pulseview (one of my favorites) with the cheap LA.
-- https://sigrok.org/wiki/PulseView
Here's a little SPI TX demo with smart pins and captures using the Saleae and the cheap LA. I uses a 1MHz clock for the demo because the cheap LA doesn't have great sample rates -- again, it's good for learning and experimenting.
Update: Fixed a gotcha in the code and added a method that writes SPI data via smart pins in PASM. Spin2 has great features for learning PASM.
I agree with Jon. The cheap $13 La works great withe Pulseview. I also have it working with an old version of Saleae, but the may have updated the software to disallow none compliant hardware. It's worth a shot, but Pulseview is a great Open Source program.
I also have a Salea PRO16 but I never pull it out.
https://usd.saleae.com/products/saleae-logic-pro-16?variant=7076781097020&variant-sku=SAL-00116
BUT This one might be more interesting to Parallaxians because it's open source:
https://github.com/fhdm-dev/scoppy
Edit: The Android bit:
https://play.google.com/store/apps/details?id=xyz.fhdm.scoppy
My brand new unit wouldn't work with the older "believed-to-be-good" software and so I tried the latest version and it works fine
Craig
I have a couple Saleae analyzers and they're great but I think I'd go with one of the cheap ones now.
If you want an oscilloscope, the Rigol DS1054Z seems to the favorite cheap scope these days (at least it was the last I checked). I like my DS1054Z.
Even if you get an oscilloscope, a logic analyzer is a good thing to have too. I think there's a way for the oscilloscope to decode various serial protocols but it's a lot easier to do this with a logic analyzer.
Dave Jones (EEVBLOG) has a couple videos on the DS1054Z oscilloscope.
You can find the Rigol DS1054Z sometimes for $399. The 50Mhz scope can be hacked to become a 100 Mhz model and all funtions enabled,
https://www.instructables.com/How-to-Hack-Upgrade-a-Rigol-DS1054Z-Digital-Oscill/
Don't ask me how mine became a 100Mhz scope.
A friend suggested the Siglent 1202X-E and I've been very happy with it.
Nice price with serial decoding buit in!
It sounds like what I really will benefit the most from at this stage is a logic analyzer.
My wife could also benefit...!
If money isnt a huge issue, get the Salea. I have the 16-channel and I love it. The software continues to evolve and it continues to surprise me with new decoders, features, etc. If you can order it from a bona fide .EDU account, the company offers STEEP discounts. Tech support is first-rate, US-based, and when there are “deep” questions, the T/S guys can literally holler over the top of their cubicle at the guys who write their code and dev the hardware. (The $20 knock-offs are honestly pretty darned good, but dont expect any support except from other users… and you should expect a few quirks here and there).
The Rigol1054Z scope is pretty sweet, especially at the current price. Mine somehow does 100 mhz and has all of the software upgrades installed… go figure. 😜 I use it constantly, and learn something new every time I turn it on. I was so impressed with Rigol’s value/price that the entire rest of my bench is Rigol: 5-1/2 digit bench meter, 20 mhz arbitrary function generator, 3-output programmable power supply, programmable DC load, and a spectrum analyzer with tracking generator. Most can be “hacked”, and nearly all talk Rigols intrument protocol. It isnt Tek/HP/Keysight quality, but its like 1/10th the cost.
I tend to use my 'scope for analog signals and the LA for signal decoding -- it's much easier to setup the decoders in the LA software.
For grins I made another smart pin test program; this one for serial output. Newcomers: Don't be afraid to write a lot of small test programs like this. Isolating new topics makes them easier to learn.
So what can a scope do that a logic analyzer can not? (Sorry for the noobish questions!)
[Jon's opinion] While many logic analyzers have analog inputs, LAs are really suited to analyzing digital signals, and the relationships between them. As you can see in the SPI capture images above, the relationship between the CS, SCLK, and MOSI pins is really easy to to see. Oscilloscopes seem to favor viewing and analysis of analog signals, especially complex analog signals.
Lots. My LA is 16 channels. Very handy when debugging a parallel bus or many different signals. But the LA biggest perk for me is being able to record a few hours of data and then roll through it with the mouse, zooming and panning as needed. You can also setup trigger conditions, and its entirely possible to set unrelated decoders up on different signals (ie, I2C on Pin 1 and 2, Asynch serial on 3/4, one-wire on 5, SPI on 6/7/8…)
In contrast, oscopes are usually a max of 4 channels and are very limited in the length of what they can display, and most can only decode one or two channels at a time (although this is changing!)
As Jon says, I mostly use the LA for logic, and the scope for analog (or when a quick-and-dirty digital look-see is all I need).
ADDIT: also, size! The LA is the size of a deck of cards. It travels nicely! The scope is a brick, so it stays home mostly.
I have a 4-channel 300MHz Tek scope ($$$) that I've had for years. It's an analog scope but has multiple triggering modes that make it very useful for digital stuff. For example, I can make it trigger on an I2C START condition so I can look at traffic on that bus. It includes video triggering that allows me to select any line in a chosen even/odd NTSC field. It also includes a rudimentary spectrum analyzer function and a ton of measurement functions (e.g. frequency, pulse-width, etc). I've never felt like I've needed anything more, although decoding serial data would be nice, so I don't have to do it by hand.
The biggest issue I have with it right now is that it uses one of those obsolete Dallas Semiconductor battery timekeeping RAMS for time/date and system settings, and the battery died. So I have to reconfigure it from the default settings every time I power up. Ugh.
-Phil
Here's a couple screen grabs from the last few times I used my logic analyzer and my oscilloscope.
Here's a trace of an I2C read from a real time clock.
The above was taken with my logic analyzer. Most logic analyzers include software to read I2C and other serial data.
Below is a capture from my oscilloscope. I was testing out the P2's DACs and made a little algorithm to generate a sinusoidal output. The oscilloscope lets me see this analog signal.
If I tried to capture the above sine wave with a logic analyzer, I would have seen a square wave instead. Most logic analyzers just detect if the line is high or low. LAs generally don't capture this sort of analog output.
An oscilloscope really shines when capturing stuff like analog audio and video signals.
The Rigol DS1054Z oscilloscope has four channels. Four channels isn't very common in the budget scopes. I rarely need more than two channels myself but the few times I've needed more than two channels I was really glad to have them.
The odds are, if you don't know why you need an oscilloscope, you probably don't need one. I'm not sure I honestly NEED one myself but I'm really glad I have it.
Not the cheapest, but I went with the Analog Discovery 2. 16 channels of logic, scope, waveform generator and +/-5 variable supply. The support software is really nice as well, Waveforms, and it comes in linux and windows flavors.
Given the specs, I think it's a great deal, at least compared to Saleae's equivalent offerings, is DreamSourceLab's DSLogic line. I have a 16-channel, 1GHz model, U3Pro16 that's $299. The 32-channel model is $399.
Truth!
>
This sounds like what I want to accomplish. I put a Saleae in my wife’s Amazon cart. Our 31st anniversary is in a few days. Perhaps she’ll take the hint. LOL!
Well played, friend. Well played.
Turnabout is fair play. What have you found in your Amazon cart that you didn't put there?
-Phil
Troubleshooting digital logic often comes down to analog problems, things like incorrect voltage levels or runt pulses that show up on a 'scope but are not seen by a strictly digital analyzer. Tools like the Saleae or the Analog Discovery include analog oscilloscope capability on top of the strictly digital, so you can fall back to that analog level if things go bump in the night.
Consider the bandwidth of the signals you want to observe. That spec is indicated by the sampling rate of your LA or 'scope. The low cost logic analyzers may sample at 25MS/s, and that is fine for signals up to the low MHz range. The Saleae and the Analog Discovery sample digital signals at from 100MS/s to 500MS/s, depending on the model. Also, they can sample analog waveforms at high enough rates and resolution for a 5 to 12 MHz analog bandwidth. That is important if you want to look at things like the rise time of digital signals, or at the fidelity of an audio output. What you choose will determine what you can look at reliably from the smart pins.
The Analog Discovery also offers digital and analog waveform generators, a host of capabilities really, that might be useful for your experiments with the full range smart pin capabilities. It is designed as an educational tool.
I do have a professional 1GHz LeCroy 'scope, for my business. I recently upgraded in order to get the protocol decoders. One useful thing on a 'scope are math and statistics and filtering capabilities. Lower end 'scopes are also gaining those functions as technology advances. For example, one trace displays an analog waveform for the amps drawn by a cellular modem, another displays a zoomed version of pulses during transmission, and a third trace shows the integral of the waveform, to get at the power supply draw per event. Another case: Right now I'm trying to reverse engineer a black box signal exchange (a hydrology instrument) that sends and receives a bipolar signal that looks and decodes like RS232, but the tx and rx are at widely different levels--that is the kind of signal you could only figure out on a real 'scope.
Thanks everyone for the great comments and suggestions! Ultimately I think I'll start with a logic analyzer and get a 'scope later.
Paul
Get a discount code from Saleae. Not sure if it works on amazon or if you have to order directly from them. It was easy and saved me a couple hundred dollars.
https://blog.saleae.com/saleae-discounts/
Thanks for the link I just ordered myself on with cables!!!
I might be biased. but I own a 'scope. And the big guy is a TEK 2213. While it certainly does not do everything that four channel one that you own @"Phil Pilgrim (PhiPi)" it certainly can do a lot. Now I've looked at the current gang from Agilent, now Keysight, and while they do have one selling point, which is that the user can manage them via the PC and using a Windows program called VEE. But what does this have to do with a 'bot sitting by the road nearest @Publison and is holding a sign that says "California?"