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

 

Shopping for my first Oscilloscope

My new project is going to involve testing and designing electronics, and so I find myself in need of a bunch of tools I don’t have. Foremost among them, is an oscilloscope, so I can probe circuits in devices to try and understand how they work, and why they don’t work.

My overall electronics aptitude is pretty mediocre. I had a job soldering connectors to serial cables when I was a kid, but my soldering skill isn’t very high and most of the electronic theory I learned in my introductory physics course in college is long forgotten. I have used an oscilloscope though. I used one when I learned about electrophysiology techniques for looking at the activity of individual cells, and I also used one to tune the video system of a cell-florescence microscope to take full advantage of its dynamic range.

More important than what I’ve done with oscilloscopes is that I know what I’d use one for now. I think it will come in handy for looking at the operation of DC-DC power supplies, and just generally for probing circuits. Beyond that though, I’m a novice, and so I went looking a place to get advice. Actually, I didn’t have to look, because I’d already found the EEVBlog Forum, which even has a special section where people are supposed to go easy on beginners for asking dumb questions. Still, they ask that you provide plenty of information when you ask a question, so I had to do some shopping on my own, so I could get a sense of the questions I should ask, and the background I should give.

My first stop was to see what Sparkfun and Adafruit, two online stores that specialize in electronics for hobbyists, were offering. Adafruit has two options, one a 50MHz, two-channel Rigol DS1052E digital storage oscilloscope, the other, a Rigol DS1102, is very similar, but has 100MHz bandwidth. Sparkfun offers the Gratten GA1102CAL, which is also a 100MHz, 2-channel digital scope. They also have two USB scopes for use with your computer, the MSO-19, and MSO-28 from link instruments. Sparkfun and Adafruit also both carry the small, inexpensive DSO Nano and/or DSO Quad.

I’d been considering a DSO Nano or Quad because of their low price and compact size, but people who seem to know better hate them, first because their user interfaces are difficult to use compared to a real oscilloscope, but also because they can’t actually do much. Of course, my needs, as I understand them, aren’t that demanding. I think the signals I’ll be looking at are in the 1-2MHz range, which should be within the capabilities of the DSO Quad, but it doesn’t leave a lot of headroom, and at $200 bucks, its a bit too expensive given that you could get a more capable used analog scope for less, or a new digital scope for another $50-100 more.

I also considered a USB scope. They are more compact, and I also assumed they’d be cheaper, since they didn’t have to include a screen or UI, and I also thought it might make it easier to work with the data on a computer. I was wrong on multiple counts. USB Scopes are a bit of a niche item when compared to a benchtop scope, because regular O’scope users find physical knobs and buttons more productive and easier to use than the often poor software that ships with USB scopes. As a result, volumes are lower, and there is less competition to drive prices down. Moreover, screens are pretty cheap these days, so eliminating one isn’t a huge cost savings. Put the two together, and a decent USB scope is about as expensive as a dedicated scope with similar specs, and you can hook most dedicated scopes up over USB if you need to anyway.

Exploring the existing options helped me think through what I needed and why. I was ready to ask the experts over on EEVBlog. I’ll cover that in my next blog post.

SATA 3.2 heralds tiny but very speedy SSDs ·  LinuxGizmos.com

Aside

The Serial ATA International Organization SATA-IO has ratified the SATA 3.2 storage spec, adding support for a SATA Express spec that can piggyback on faster PCI Express lanes, and defining a new embedded single-chip microSSD. SATA 3.2 also embraces the tiny, SATA Express based M.2 form factor, which debuted in recent Intel and Samsung SSDs.

via SATA 3.2 heralds tiny but very speedy SSDs ·  LinuxGizmos.com.

Acu-Link Bridge and Acu-Rite Weather Station Teardown

I got an Acu-Rite Weather Station as a gift and, of course, I cracked open some of the parts to see what was inside.

I didn’t open up the 5-in-1 sensor unit which sits outdoors and measures wind speed & direction, temperature, humidity and precipitation. I did crack open the 01500RX display console, and the Acu-Link bridge which receives the sensor data over a wireless link and relays it to the Acu-Link webservice via an ethernet connection.

The 01500RX had a number of blob-top chips-on-board. I didn’t try to figure out what they were. I was most interested in the wireless receiver that picks up sensor data.

IMG_3645

The receiver was on its own PCB.  The chip is labeled MICRF211AYQS 1226, which seems to be a 433MHz RF receiver from Micrel with a demodulated signal output.

In the internet bridge, I found the same receiver, along with a low cost ethernet enabled microcontroller, and a surprise.

Acu-Link Bridge PCB

 

The microcontroller is a PIC18F67J60, very bare-bones 8-bit chip with an ethernet port, 128K of flash, less than 4K of RAM, and 8K RAM for the ethernet buffer. This is apparently enough to run a TCP/IP stack with a bare-bones web server, but it doesn’t exactly leave a lot of room for adding additional functionality, like the ability to make sensor data available locally via HTTP.

I also mentioned that there was a surprise. You can see it too, in the lower left of the photo, a third PCB, this one, apparently holding a serial to RF transmitter. I don’t know what it is for. Acu-Rite doesn’t talk about it at all in any of the marketing materials or users manual. My guess is that it might work as a repeater for the sensor data, that, or they’ll have some actuator equipment in the future, like, say, something that could toggle the mode on an automatic irrigation system based on local weather conditions.

Anyway, that’s what I found. I thought it might help out other people who are intrigued by Acu-Rite’s offerings and interested in hacking them for their own purposes.