Keithley 2000 RS-232 Serial WTF

My Keithley 2000 DMM craps out during serial communications with a PC over RS-232.  When it does, the voltages on the TxD (yellow trace) and RxD (blue trace) lines look like this:

19.2kbps Fail KE

There are a few things wrong here.

  • The idle voltage of the RxD line should be -7v or so, similar to that of the TxD line, rather than the -1.7v it starts at.
  • The obvious decline in signal quality before the RxD locks at the ~1.2v shown at the end of the trace.
  • RxS locks at 1.2v, rather than returning to it’s idle voltage.

I came across someone who had trouble with the RS-232 level shifter IC on the similar Keithley 2015, so I carefully checked it out. It seems to be well under-spec on the output of its internal -10v power supply, which can only deliver a sustained 6mA. The +10v supply, on the other hand, can provide much more. I also diligently checking of voltages and current delivery of all the signal lines both the multimeter and the USB to RS-232 adapter its connected to.

It appears that the PC is trying to drive the RTS line to +7v. At the same time, the multimeter is trying to drive the RTS line down to -9v, and its loosing. As a result, it can’t drive the RxD line below -1.7v, and eventually, while transmitting, it gets stuck at +1.2v.

But why is the the DMM trying to do anything on the RTS line. That’s the job of the “data terminal equipment” or DTE for short. I checked the reverse-engineered Keithley 2000 schematic, and it shows that the RTS line is connected to one of the transmit outputs of the level shifter IC, something I confirmed by doing a continuity test. This makes no sense to me.

If I disconnect the DMM from the RTS line, everything seems to work fine. The DMM drives the RxD line to -9v at idle, and sustains signal quality throughout a transmission.

RxD is in much better shape when RTS isn't connectedI can’t imagine I’m the first person to come across this. I’m surprised though that I can’t find any mention of it online.

Update:

I posted about this in the EEVBlog Forums and a few users provided some details of similar issues they’ve had with RS-232 communications on the Keithley 2000 DMM. None of them have gone as deep as I have, but their descriptions are explained by my hypothesis.

I’m interested in whether later versions of the firmware leave the RST pin floating. So far no one with more recent firmware has checked for me, but one user remembers someone getting a similar problem fixed with a firmware update.

I’ll probably try doing a firmware update on my own. One user reports that he figured out he could use some Flash chips replace the EPROMs, which is attractive because I can re-use the chips and I don’t have to buy a legacy device like an EPROM programmer.

In the meantime, I picked up a straight-through male-to-female DB-9 cable and clipped off the RTS pin (#7). With it in place between the USB RS-232 adapter and the DMM, I ran a test querying the DMM with “*IDN?” every second for an hour or so. The DMM remained responsive for the whole time, and the responses it sent were complete, and uncorrupted. Previously things crapped out within a few minutes and only a few commands.

Keithley 2000 “Repair” Tip

I won an auction to buy a Keithley 2000 6 1/2 digit multimeter on Ebay for ~$250, a pretty good price. The seller said it had some scuffs, but was “tested and ready for work.”

When I received it, it was clear that it was a little worse for wear than claimed. It had a cracked rear bracket, and a yellowish/brown tint, rather than the shades of grey of a new machine. At first I thought it might be yellowing due to sun exposure, but the yellowing seemed to afflict the painted metal case as well as the plastics.

It did power up, and when I tested it with a voltage reference I have, its readings came in pretty close to the expected value, so I didn’t worry too much about the physical condition beyond trying to wipe the outside down well with cleaner and isopropyl alcohol.

Once I’d done that, I decided to look inside, to see if I could get an idea of the manufacture date. As soon as I removed the case, it was obvious where the yellowing had come from. It stank of old tobacco smoke on the inside, though fortunately, there wasn’t an obvious film. As I looked around, inside I could see a number of components with date codes for mid 1995, which matched well with the date of the first and only calibration, November 1995. It was almost 20 years old.

In the process of looking at the insides, I noticed that he input wires seemed a little close to some metal projections from the input selection switch, which seemed a little sloppy. Then I realized the board seemed a little slanty, and was out of its mounting tracks, possibly it had been jarred loose in an impact. On the opposite side of the chassis, I saw that some wires to the front panel and the power transformer weren’t routed through a retaining clip. Someone had taken this thing apart, and done a poor job of putting it back together. I loosened some screws so I could slide the board back into position and noticed a gouge in the PCB when it had been forced into place during a previous reassembly. Fortunately, it only damaged some solder mask, and not the trace underneath.

Once I had it back together, I ran the self-tests and was discouraged when it reported a number of faults for tests 100.1, 101.2, 101.3, 200.1, 200.2, 201.1, 201.2, 300.1, 301.1, 301.2, 302.1, 302.2, 303.1, 303.2, 304.1, 400.2, 401.2, 402.2, 403.2, 500.1, 500.2, 600.1, 600.2 and 601.2. That’s most of the self tests.

I tried to work through the troubleshooting in the repair guide, but it was dismal, it didn’t even describe the signals on the half-dozen or so test points on the board. I found a reverse engineered schematic and dove in.

I was working my way around the A/D chip trying to orient myself to the various signals, when I noticed…something. At first I thought it was a stray line on the silkscreen, but on a closer look, it seemed to be a fiber, cat hair? Dog hair? I flicked it away with my gloved hand, and then blew the area clear with some canned air.

I reran the tests and they all passed! One tiny fiber in the wrong place was enough enough to through the A/D converter out of spec cause a cascading failure.

The cheapest/best 2012 Retina Macbook Pro SSD Upgrade

Long-time Retina MacBook Pro owners finally have some reasonable storage upgrade options. Apple has used proprietary SSD form-factors and connectors for their thin notebooks since the second generation MacBook Air was released, but they’ve always used standard storage protocols, like SATA.

I’ve long hoped that someone would come out with a simple, inexpensive adapter that would allow a commodity mSATA or m.2 SSD in my Retina MacBook Pro, but I could never find any on the market. When I needed more storage, I decided to supplement my original SSD by fill my laptops SDXC slot with a 64GB micro SDXC in a shortened microSD-SD adapter. It wasn’t exactly cheap, or fact but it was affordable, worked well enough. OWC offered an upgrade for the original SSD, but it was relatively expensive, particularly since I replaced, rather than augmented the original storage, and it was slower than the stock option.

I knew I’d outgrow the add-on card someday. I was heartened that some companies offered larger, higher-performing shortened SD cards, and that Trancend released a line of Apple upgrade SSDs to compete with OWC, but I still thought an adapter would be the best approach. I gave more than idle thought to developing and selling my own adapter, since no one else was doing it.

In the meantime, I managed to keep ~40GB free on the original SSD. Then, this past week, all that space filled up almost overnight. I’t seems that a 15 video I was editing in iMovie resulted in the creation of lots of temp files. I tried to make more space, by copying stuff to a server, and I succeeded well enough to have enough room to finish editing the video. I knew though, that it was time to find an upgrade.

The OWC options still weren’t very compelling, and my next step was to see what the market for original equipment SSDs was on eBay. The prices weren’t too bad, if I could put aside concerns about the quality and provenance of the drives. I decided to search for adapters, and didn’t find anything at first, but stumbled across a company called MaxUpgrades, that was selling Samsung EVO 840 SSDs with an rMBP adapter for non-obscene prices (Warning: BAD website).

With more digging, I found similar, if not the same, adapter cards were on Amazon for ~$20 and on eBay for ~$10. So, I ordered the adapter, a 500GB Samung 840 EVO SSD, and another adapter that would let me use the mSATA SSD with a USB3/SATA adapter cable I already had to migrate my data before installing it in my Macbook. It only took a few days for all the parts to arrive, and an hour or two to get the data copied and install the new SSD + adapter in my computer.

Everything was pretty straightforward. I think the one thing that I wasn’t sure about was how to transfer everything to the new SSD. I originally settled on using demo version of Carbon Copy Cloner, but then I realized that I could do what I needed by rebooting in recovery mode, running Disk Utility, and then restoring to the new SSD using the old SSD as the source. In addition to moving the OS install and all my data, DiskUtility automatically creates a new recovery partition.

Once that was done, I rebooted from the new SSD over USB to check to make sure it worked before shutting down and installing the new SSD, with the OS, data and everything already transferred. Once I had everything back together, it booted right up.

I’ve ordered an adapter that will let me use the old Apple SSD in place of a 2.5″ SATA drive. I’ll probably put it in a case with an integrated USB3 adapter and use it for extra speedy storage and backup.

A few things to consider before doing this yourself:

  • The mid-2012 and early-2013 retina MacBook Pros (MacBook Pro 10,1, A1398) use the SATA 6Gbps protocol to connect to SSDs. Later models use PCIe, but I don’t know if the necessary adapters exist.
  • This upgrade might create issues if you are still under the original or extended AppleCare warranty. In theory, “user replaceable” parts don’t invalidate the overall warranty in the US, but Apple might argue that their SSDs are no longer user-replaceable.
  • Opening up an rMBP and removing the SSD requires a special pentalobe screwdriver. I used this inexpensive toolkit, which has the necessary bit, and many others.
  • Cheap Chinese electronics from ebay can be a great deal, but the quality and documentation is inconsistent. Compatibility (and incompatibility) information should be taken with a grain of salt.

Fish8840 AVR Transistor Tester Review

Today, I’m looking at a neat gadget I got on ebay for about $20 called the “Big 12864 LCD Transistor Tester Capacitance ESR Meter Diode Triode MOS NPN LCR.”

There are hundreds of listing for dozens of variations of these under different names, for prices ranging from ~$12-40.  Most, if not all of them, are made in china. Most, if not all of them, are descended from the AVR Transistor Tester project by Markus Frejek (or google translated), with further improvements by Karl-Heinz Kübbeler (or google translated). Unforunately, none of the Chinese clones honor the projects license and release source-code for their firmware modifications. Fortunately, people are figuring out the hardware differences on some of them, and adding support for to the open source project. The english language documentation for the project is great. It actually includes information on some of the chineese clones. Even better, the design and documentation are a great example for learning how to make good use of the hardware on an AVR MCU.

The Fish8840 version I have, which has a PCB date of 2014-07, has stupid bug in the power-management circuitry which causes it to have excessive current drain when it is supposed to be “off.” This video review by George Thomas of AmateurLogic.tv includes a simple modification that fixes the problem.

I didn’t really love this one. In addition to the flaw described above, some of the graphics are hard to read. Plus, there are rumors that the hardware is locked to block installation of different firmware.

For more information:

Animated Crashplan Icon Causes Window Server to Burn CPU on OSX

I use Crashplan for backup on OSX. Tonight I happened to notice that the OSX windowserver process was consistently burning ~25% of a CPU core on my Mac for no reason. I also noticed that Crashplan was backing up my computer at the time.

I decided to try switching the preferences for the Crashplan menu bar icon to disable animation, windowserver’s CPU utilization dropped. I turned animation back on it jumped back up.

Someone should change the default.

Quick impressions: iOS 8 on the iPhone 4s and iPad Retina (3rd generation)

I installed iOS on both my iPad Retina (3rd gen) and my iPhone 4s. I had some misgivings, since they are both at or near the bottom of the barrel in terms of supported hardware for this release. After some research though, it sounded like the iPad would do reasonably well. As for the iPhone, well, I should have a newer model in a week or two if it doesn’t work out.

My report is that both of them seem to work just fine. There may be a few more rough spots and hitches than before, but if there are, they are rare and subtle (for the most part), and they are counterbalanced by new features and refinements.

One issue on the iPhone 4s is that all the other models supported by iOS have taller displays, and so some UI is more suited to larger phones. The only place where this really stands out is when composing an email. Between the predictive text selections above the keyboard (which can be hidden, if desired) and the new UI affordance for easily switching between the email you are drafting and other messages, there isn’t much room to read the text you are writing.

There are definitely signs of memory pressure though. Tabs in Safari need to reload more (too) often and switching between some apps can take a little too long.

My advice for iPhone 4s users is to wait until they release a round of bug fixes, unless you absolutely need to try the latest and greatest.

As for the iPad, I don’t notice many differences in interaction experience from iOS 7. Safari may need to reload tabs a bit more often, but no where near as often as on the iPhone.

My advice for anyone with a 3rd generation iPad, or better is: If you want it, go for it.

If you want to know why you’d want to upgrade in the first place, there are lots of reviews of what’s new in iOS to choose from. Its worth noting though, that some features aren’t available on all devices. It looks like my devices will be left out of some of the seamless handoff as you move from a Mac to your iPad, or vice versa. One thing that just worked though, incoming phone calls show up on my iPad, and I can choose to answer them there, if I want. Not a huge deal, but convenient in some situations.

Still Shopping for my first oscilloscope, but it’s selection time!

I recently decided to buy my first oscilloscope to help with the process of learning more about electronics. The process of selecting an oscilloscope has been longer than expected. I started by looking at the scopes that Sparkfun and Adafruit offered, which lead me to wonder what other options were out there. I was a bit overwhelmed at the variety of models and manufactures, but managed to cut through a lot of the noise.

In this post, I’ll talk more about how I narrowed things down further, and what I ended up choosing.

To start, its worth covering why I wanted an oscilloscope in the first place. It all stems from a growing interest in the declining costs of capable “systems on a chip,” low power communication technologies like Bluetooth LE, and even WiFi, and the accessibility of the Chinese electronics manufacturing supply chain. Taken together, it seemed to me that I should learn enough about electronics to have a sense of the possibilities and limitations, and to be better able to collaborate with people with deeper expertise. This approach served me well in the past when I worked on software projects; I wasn’t a programmer, but I understood enough to be a good collaborator.

In looking around for learning projects, I decided to explore the world of power sources for these devices with a new site called Power Cartel. Part of what I’m doing on Power Cartel is doing teardowns of battery packs and chargers, with the goal of collaboratively creating useful opensource designs. In order to dive deeper in my teardowns, and support my own design efforts, I need to be able to start exploring what is happening inside the circuits and understanding how the different components interact.

There are a lot of test instruments. I already have a basic multimeter, but I felt like I needed a way to look at signals over time. There are two instruments that fit that job description. A data logger or chart recorder is useful for looking at signals over long periods of time (ie hours), where as an oscilloscope is good for looking at signals over much shorter periods, seconds down to micro, or even nanoseconds. I actually want to look at signals over both time periods. I want to look at current and voltage for charging and discharging batteries over the period of hours or days, but I also want to look at sub-second changes in signals.

I decided to start with an oscilloscope, rather than a data logger, because the sub-second changes are more fundamental. With a better understanding of such things, I could build my own data loggers. Moreover, most modern digital storage oscilloscopes can actually record signal changes over longer periods of time, and they can be connected to a computer for control and data recording.

I originally thought that some sort of oscilloscope module that I could connect to my computer or iPad would be a good place to start because it would save me money and space. I quickly learned there were problems with that approach. Most electrical engineers and technicians are trained on traditional stand-alone oscilloscopes, and training aside, traditional stand-alone oscillosopes are often easier/faster to work with because they have dials and buttons arranged in a user interface that has seen steady improvement for close to a century. Connected scopes are newer, and more of a niche item, so their software is less refined. More importantly, because they are a niche item, there is less competition and scale to push prices down, so any savings that might come from omitting a screen and controls is offset. As a result, USB scopes are not any cheaper than stand-alone scopes with otherwise similar specifications. The space savings was still attractive, but I decided I was going to purchase a stand-alone scope.

With that decision made, I had to figure the other key specifications for my work. For any scope, whether an older analog scope, or a more modern digital storage scope, bandwidth is a key consideration. Bandwidth determines the range of signal frequencies you can measure with the scope. Adafruit sells scopes with 50MHz and 100MHz bandwidth. Sparkfun’s stand-alone scope offering is 100MHz. From a little reading, the switch mode power supplies I’m going to be working with typically operate in the range of 200KHz to 2MHz, and the microcontrollers I’m working with operate at 4-16MHz, or perhaps 50-70MHz. Some of the wired communications protocols I’m using may be 5MHz.  It would seem then that a 50-100MHz scope would cover almost anything I’m likely to use it for in the near future.

Closely related to bandwidth is the sampling rate. Sampling rate is the number of times per second a signal is read. For a pure sine wave, an accurate estimate of frequency and amplitude requires a sampling rate that is at least two times higher than that of the signal being measured. One of the big reasons for having an oscilloscope though is to look at signals that are not pure sine waves. A lot of digital communications use square   wave signals, and a lot of signals, whether square, sign, step, pulse, or something else, can get distorted by characteristics of the circuits they travel in. A rule of thumb I’ve come across is that the sample rate should be 4x the frequency of the signal you are observing.

Almost all the scopes in my price-range ($400-650) have a 1GHz max sample rate. That may sound like overkill for a 100MHz scope, but in this segment of the market, that sample rate is across all the channels of the scope. So, if you have a scope with two channels, and you are using both of them, thats a 500MHz rate per channel, which is closer to the rule of thumb.

The next thing I considered was the number of channels. Each signal you measure requires a channel. Often you are comparing two signals against each other some how, and so, not surprisingly, most scopes have at least two channels, and, indeed, in this entry level segment, most don’t have more than two channels. I found a few with four channels, though. Most were out of my price range, but one, the Rigol DS1074Z was available for under $600. A two channel scope would probably do everything I reasonably needed, but the option of having four channels was intriguing. Four channels would allow me to look at voltage and current at the same time for both the input and output of a power supply. Even better, I could use some of the channels as a basic logic analyzer, and look at how analog signals changed in relationship to specific digital signals.

The consideration of the number of channels also turned my attention to scopes with a logic analyzer option to look at even more digital signals. Oscilloscopes with this feature are generally called Mixed Signal Oscilloscopes, which add 8 or 16 logic channels. The added digital channels come with an added cost. There is a $600 mixed-signal scope from Rigol (DS1052D), but it only has two analog channels, 50MHz bandwidth, and 1Mpts of memory. The Rigol MSO10747Z, which is the mixed signal version of the DS1074Z is $250 more expensive, and out of my price range. Since people seemed less bothered by USB logic analyzers, and since a cheap one could be had or $20 or so, I decided that I didn’t need a full logic analyzer.

Another consideration is the amount of memory available to hold samples. The Rigol DS1074Z has memory for twelve million sample points (12Mpts). Some of the alternatives I considered, like the Siglent SDS1102CML only has 2Mpts of memory, and the Siglent SDS1074CFL only has 24Kpts.

By now, you’ve probably figured out the DS1074Z is the scope I’m leaning towards. I took repeated looks at the other options from Rigol and Siglent, but kept coming back to the DS1074Z.

Comparison

Cheaper

  • Siglent SDS1072CML for $319: +lower price -2 channels -memory
  • Rigol DS1052E for $329 +lower price -50MHz -2ch -smaller screen – older
  • Siglent SDS1102CML & SDS1102CNL ~$360 +lower price +100MHz -2ch -smaller memory -can’t tell how they differ from each other, other than memory
  • Gatten GA1102CAL $400 +lower price +100MHz -2ch -smaller memory

I would have liked spending less, but I wasn’t willing to go with a last generation Rigol, or forgo 2 channels and a bunch of sample memory just to save $150 or so

Similar

  • Siglent SDS1202CNL+ $546 +200MHz, 2Gigasamples/s -2ch -memory
  • Rigol DS1052D $610 +16 channel logic analyzer, -2ch -memory

The higher bandwidth and sample rate of the Siglent just didn’t seem that compelling, and nor did spending another $60 for the 16-channel logic analyzer on a last generation instrument.

More Expensive

  • Siglent SDS1074CFL $723 -higher price +2GSa/s, =4ch, – memory
  • Siglent SDS2072 $805 -higher price, +2GSa/s +memory -2ch +larger screen
  • Rigol DS1074Z-S $818 +signal generator
  • Rigol DS1104Z $830 +100MHz bandwidth
  • Rigol MSO1074Z $835 +16 channel logic analyzer
  • Rigol DS2072A $839 -higher price -2ch +2GSa/s

The price was really enough to knock all of these out. The Siglent SDS1074CFL was tempting since it had 4 channels and a higher sample rate, but the higher sample rate isn’t that important to me at this point, and so not worth the extra $175 or so. The only other one I gave serious consideration to was the MSO1074Z, but the integrated logic analyzer just didn’t seem compelling enough to drop another $280 or so.

Finally

In the end, the Rigol DS1074Z won me over with its combination of price, four channels and deep memory, along with the fact that Rigol seems to be a well-understood quantity at this point. This model has been out for almost a year, most of the bugs are known, and many have already been address. There are lots of good in depth reviews and tutorials for Rigol scopes. Certainly more than I saw for Siglent/Atten/Gatten or Owon.

The Rigol has another thing in its favor. It apparently shares the same hardware as the DS1104Z, and people have figured out a way to unlock the higher bandwidth. They’ve also figured out how to unlock some otherwise extra cost after market options, most of which don’t interest me, but its nice to have the option.

I ended up ordering my scope from TEquipment.net, and paid less than $585 with free shipping thanks to a discount they offer members of EEVblog.

 

 

Apple Event Live Blog September 19 2014

In which I sit in my office in Seattle, watch the Apple live stream and comment on it:

  • 10:04am PDT
  • I still see the test pattern and schedule. This never would have happened when Steve Jobs was Alive.
  • 10:06am
  • Time Cook is on, and then the bars come back…
  • 10:08am
  • Ok, its working again…and fail.
  • 10:11am
  • It is working again, for now…
  • Bigger phones, um, hooray? I guess.
  • Phil is talking about % more pixels. Lame…
  • Now he’s finally talking about why that matters: two up view.
  • Thinner is good though, I guess, as long as it feels solid.
  • What is with the translation track?
  • And the stream breaks again…
  • Something about apps taking advantage of larger displays.
  • Desktop-class scaler?
  • 10:24, it is working again…
  • A8+METAL = FAST GRAPHICS
  • BETTER BATTERY LIFE
  • New M8 co-processor.
  • Distance and elevation estimation.
  • Ok, so, I do want one, just to be clear. My iPhone 4s seems a little too old now.
  • 10:28am
  • Cameras
  • Hmm. Focus pixels?…   Phase detection autofocus!!! Fast autofocus!  YES I MUST HAVE THIS!
  • Something about the macro mode that I didn’t catch.
  • 10:34am
  • Apple broke the internet.
  • 120 or 240fps video. Sweet
  • Continuous focus for video…
  • 10:36am
  • More stream breakage
  • 64GB for the mid-range for $299 on contract!  Yay
  • $100 for thoe the 6plus
  • Steady incremental improvement can really add up. I was pretty “meh” leading up to this event. I felt the same way when it started, but everything adds up.
  • The payment stuff seems pretty important, especially the API…
  • One more thing…
  • It would be really really awsome if it isn’t a watch.
  • Its a new planet!
  • And the space ship that will get you there
  • No, it really is a watch…
  • I must say, it looks really cool…
  • …for a watch.
  • I’m so over watches…
  • At least I thought I was…
  • For 10-15 years…
  • At least it isn’t called iWatch.
  • The personal touch stuff is really interesting…
  • I wonder if 3rd party developers will be able to create “watch face” apps.
  • I look forward to the bio-mimetic bands for the next version.
  • They will graft themselves into your skin.
  • Or rather, your skin will incorporate them.
  • This is a long-ass video.
  • Why does Kevin Lynch seem familiar…
  • He’s the former Adobe Flash Evangelist
  • Gruber called him a bad hire for Apple…
  • Coldplay?  What a fucking bozo.
  • 3rd party dev support sounds pretty good.
  • I’m running out of steam here…
  • I wonder how the Apple watch works when you don’t have your phone with you?
  • The live stream was working so well, until, another fail.
  • So, if Apple Pay is built into Apple watch, and Apple watch works with many versions of iPhone, plus all the accessories, Apple has multiple revenue streams for the Apple watch. I wonder if the pricing will be subsidized.

Still shopping for my first oscilloscope

Earlier I wrote a long blog post that condensed down the path I’ve taken to buying my first oscilloscope. I hadn’t decided what to buy though., so this post will continue with more of the decision making process.

But first, a short review of the ground I covered in my earlier post. I explained that I needed an oscilloscope to help me better understand why circuits work, or don’t work. I’m not just doing this for fun, my goal is to start designing and building some useful circuits of my own. I covered how I started figuring out what my options were for an entry-level scope, in order to better understand what I should be thinking about.

At the end, I’d concluded that buying a cheap compact oscilloscope like the DSO Quad wasn’t a good idea (not capable enough to be useful for long, and not cheap enough given its limitations), and why a USB scope wasn’t going to save me any money (the meager savings from omitting a screen and controls are offset by the higher prices that come with limited volumes).

I started by considering Rigol scopes like the dual-channel Rigol scopes sold by Adafruit, or the dual-channel. Gratten scope sold by Sparkfun. At this point though, I’ve all but ruled out those options. The truth is, at $390-460, they are all within my budget, and with 50-100MHz of bandwidth, they can all do what I think I’m going to need them to, which is to deal with ~1-2MHz signals from switch mode power supplies. The problem is, while I don’t know much about oscilloscopes, I’ve already figured out that I have better options.

A hint of this is already obvious among the three scopes on Adafruit and Sparkfun. Both the Rigol scopes have 5.7″ 320x24o displays, while the Gratten has a 7″ 800×480 display. Of course, even I know that while a large screen is better, screen size probably shouldn’t be the first, or even fifth thing to judge a scope on. Things like bandwidth, sample rate and memory size, on the other hand, are much more important, and here the Gratten scope matches or beats the Rigol offerings sold by Adafruit. For $400, it offers 100MHz bandwidth and it does so for just $10 more than the 50MHz Rigol scope and $50 less than the 100MHz Rigol. That might be enough to convince them to buy the Atten scope from Sparkfun, me, on the otherhand, I get curious about what else is out there.

What I found is daunting. There are so many options, I’m tempted to buy the Gratten GR1102CAL from Sparkfun and get on with things, but that wouldn’t be like me. I press on.

One of the things I notice in my research is that a lot of these scopes have similar model names. This isn’t exactly a surprise though, because often the numerical part of the name represents some fundamental characteristics. Taking the Sparkfun and Adafruit offerings as an example:

  • DS1102
  • DS1052
  • GR1102CAL

The last/right-most digit on all three scopes is the number two (2). If one were to check out more models of scope from Rigol and Atten (among others), you’d probably recognize that this is the number of input channels. Two channels is common among entry level scopes. Higher end scopes sometimes have 4 channels.

With enough perspective, it becomes obvious that the middle two digits often indicate the bandwidth offered by the scopes: 100MHz or 050MHz in the case of these examples.

The meaning of the first digit seems to indicate the model line, and the letters at the end often indicate key options, like memory size.

The similarities don’t end with just the numbers though. Model names between manufacturers seem very similar. Sometimes even the names seem similar. For example, there is the Gratten GR1102CAL sold by Sparkfun, and there is another manufacturer called Atten, which has a model SDS1102CAL; the specs are pretty much identical between the two. In fact, the case is too, down to the position of the front USB port. Oh, and then there is the Siglent SDS1102CAL, also with remarkably similar specs and appearance.

There is an explanation though, which is that some manufactures sell the same or similar equipment under multiple brands and/or sell equipment which other brands sell under their own label. This simplifies things somewhat, if you can keep everything straight.

I learned something else too, which is that while the Rigol scopes Adafruit sells were revolutionary revolutionary for the value they offered when they first came out, they are a bit long in the tooth now. Last year Rigol released the DS1000Z series, which occupies the same price point the DS1000 series originally did when it came out.

I’ve learned a lot more about the options available for good entry level scopes. Now I’m really sure that I don’t know what to buy. Narrowing down my options will have to be the subject for a new post